Scientific Assessment of Stratospheric Ozone

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WORLDMETEOROLOGICALORGANIZATION GLOBAL OZONERESEARCHAND MONITORINGPROJECT-REPORT NO.20

Scientific Assessment of Stratospheric Ozone: 1989

Volume Appendix:

NATIONAL

AERONAUTICS

II

AFEAS

Report

AND SPACE

ADMINISTRATION

UNITED KINGDOM - DEPARTMENT OF THE ENVIRONMENT NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

ALTERNATIVE

UNITED

NATIONS

WORLD

METEOROLOGICAL

FLUOROCARBON

ENVIRONMENT

ENVIRONMENTAL

PROGRAM

ORGANIZATION ACCEPTABILITY

STUDY

(AFEAS)

TABLE Io

Igo

INTRODUCTION Introduction PHYSICAL

..........................................................

Executive

Summary .................................................... Properties

of Alternatives

Chlorofluorocarbons REACTION Executive

Summary

Rate Constants for Selected

ABSORPTION

CROSS

Executive

Summary of Ultraviolet

Fluorocarbons We

TROPOSPHERIC Combined

and Recommended

Rate Constants

Tables ...............

and S. P. Sander .................

47

SECTIONS .................................................. Absorption

107

Cross Sections

of a Series of Alternative

by M. J. Molina ...................................... OH AND HCFC/HFC

Summary

41

HCFC's and HFC's with OH and

M. J. Kurylo

111

LIFETIMES

and Conclusions

...................................

123

Atmospheric Lifetimes for HCFCs Table .............................. The Tropospheric Lifetime_ of Halocarbons and their Reactions with OH Radicals: An Assessment Based on the Concentration of t4CO

124

by R. G. Derwent and A. Volz-Thomas ............................... Tropospheric Hydroxyl Concentrations and the Lifetimes of

127

Hydrochlorofluorocarbons Vlo

11

RATE CONSTANTS

Evaluated

Review

7

to the Fully Halogenated

by M. O. McLinden ...............................

O(mD) by R. F. Hampson, IVe

3

PROPERTIES

Physical

III.

OF CONTENTS

DEGRADATION Combined

(HCFCs)

by M. J. Prather ....................

149

...................................

161

MECHANISMS Summary

Fluorine-Containing

and Conclusions

Products in Atmospheric

Degradation

Table ...........

Tropospheric Reactions of the Haloalkyl Radicals Formed from Radical Reaction with a Series of Alternative Fluorocarbons by R. Atkinson ....................................................

165

Degradation Mechanisms of Selected Hydrochlorofluorocarbons in the Atmosphere: An Assessment of Current Knowledge by R. A. Cox and R. Lesclaux ................................................... An Assessment Reactions by

of Potential of Alternative

Degradation

Products

Fluorocarbons

Degradation

Chlorofluorocarbons

Mechanisms

in the Troposphere 235

of Hydrogen

(HCFC) and Fluorocarbons

Containing (HFC)

by R. Zellner .....................................................

251

iii

I_ECEDING

209

in the Gas-Phase

H. Niki .......................................................

Atmospheric

162

Hydroxyl

PAGE BLANK

NOT

FILMED

VII.

LIQUID

PHASE

Executive

PROCESSES

Summary ..................................................

269

Possible Atmospheric Lifetimes and Chemical Reaction Mechanisms for Selected HCFCs, HFCs, CH3CCI3, and their Degradation Products Against

Dissolution

andor

Degradation

in Seawater

and Cloudwater

by P. H. Wine and W. L. Chameides ................................. VIII.

OZONE

DEPLETION

Executive

POTENTIALS

Summary

Relative

Effects

273

..................................................

on Stratospheric

Ozone

299

of Halogenated

Methanes

and

Ethanes of Social and Industrial Interest by D. A. Fisher, C. H. Hales, Filkin, M. K. W. Ko, N. D. Sze, P. S. Connell, D. J. Wuebbles, I. S. A. Isaksen, IXg

HALOCARBON Executive Relative

and F. Stordal ......................................

GLOBAL Summary

Effects

WARMING

303

POTENTIALS

..................................................

on Global

Warming

381

of Halogenated

Methanes

and Ethanes

of Social and Industrial Interest by D. A. Fisher, and C. H. Hales, Wang, M. K. W. Ko and N. D. Sze .................................. Xo

IMPACT OZONE

ON PHOTOCHEMICAL

Executive

Tropospheric XI.

NATURAL

OXIDANTS

INCLUDING

TROPOSPHERIC

of Potential

Impact

of Alternative

405 Fluorocarbons

on

Ozone by H. Niki ......................................

409

SOURCES

Executive

Summary ..................................................

Natural Chlorine and Fluorine in the Atmosphere, by J. P. Friend .................................................... XII.

Wei-Chyung 383

Summary ..................................................

An Assessment

D. L.

BIOLOGICAL

AND HEALTH

Combined

Summary

Toxicology

of Atmospheric

Water and Precipitation 433

EFFECTS

and Conclusions

Hydrochlorofluorocarbons

429

...................................

Degradation

Products

by L. S. Kaminsky

451

of Selected ..........................

Assessment of Effects on Vegetation of Degradation Products from Alternative Fluorocarbons by D. C. McCune and L. H. Weinstein

455 .........

463

ANNEXES: A. Experts

and Reviewers

B. Companies C. Statement REFERENCES

Sponsoring

................................................

A- 1

AFEAS .........................................

B- 1

of Work ...................................................

.................................................................

C-1 R- 1

iv

I.

INTRODUCTION

Introduction

INTRODUCTION This report is the outcome of the Alternative AFEAS

was organized

geted to replace

to evaluate

Fluorocarbon

the potential

fully halogenated

Environmental

chlorofluorocarbons

(CFCs).

of the compounds

to affect stratospheric

• their potential

to affect tropospheric

• their potential

to contribute

• the atmospheric hence, • the potential The alternative

mechanisms

environmental compounds

effects

carbon

tar-

was to:

the environmental

acceptability

of the

ozone,

global

warming,

of the compounds,

of the decomposition

in order to identify

and hydrogen

chlorine

and

(HFCs) with one or two carbon atoms

and hydrochlorofluorocarbons

atoms and one or more each of fluorine,

their products

products.

to be studied were hydrofluorocarborns

and one or more each of fluorine

compounds

ozone,

to model calculated

degradation

Study (AFEAS).

of alternative

The objective

Evaluate all relevant current scientific information to determine alternative fluorocarbons with special emphasis on: • the potential

Acceptability

effects on the environment

and hydrogen.

(HCFCs) Because

with one or two

they contain

hydrogen

atoms, HFCs and HCFCs are less stable in the atmosphere than CFCs and thus have greatly reduced ozone depletion potentials. Additionally, HFCs do not contain chlorine atoms which are the key factor in ozone depletion.

All compounds

placed on evaluating

meeting

the above criteria

HCFC

123

CCI2HCF3

HCFC

141b

CC12FCH3

HCFC

142b

CCIF2CH3

HCFC

22

CCIF2H

HCFC 124 HFC 134a

CCIFHCF3 CF3CFH2

HFC

152a

CF2HCH3

HFC

125

CF3CF2H

The 52 scientists nex A. Experts global warming

worldwide

prepared

or more scientists.

were evaluated

where data exists but emphasis

who were involved

review papers

In addition,

potentials.

in AFEAS

on all aspects

model calculations

A meeting

are listed in at the end of this report in An-

of the topic and each paper was reviewed

were carried

was held in Boulder,

ship of Dr. R. T. Watson of the National

Aeronautics

out on ozone depletion

Colorado

AFEAS mental

was conducted from around

acceptability

by independent

scientists

but was organized

the world as part of cooperative

of CFC alternatives.

Companies

industry

(NASA)

and sponsored

participating

PAGE BLANK

for experts

and

of that meeting.

by fifteen

CFC

efforts to study the safety and environin AFEAS

3 PRECEDING

by one

and halocarbon

in May 1989 under the chairman-

and Space Administration

reviewers to discuss and reach a consensus. The papers in this report are the outcome Summaries of these papers form part of the August 1989 UNEP Science Assessment.

producers

was

the following.

NOT

FILMED

are listed in Annex

B.

INTRODUCTION The statement

of work used to initiate this project

This report consists of reviewers'

opinions

of the individual and discussion.

and the work assignments

papers prepared They are arranged

there is more than one paper on a topic, a combined the papers in that section.

for the Boulder in sections

summary

4

are given in Annex

meeting,

according

and conclusions

C.

revised to take account to subject matter.

was prepared

Where

to introduce

II.

Physical

Properties

PHYSICAL

of Alternatives

Mark

PROPERTIES

to the Fully

Institute Boulder,

Chlorofluorocarbons

O. McLinden

Thermophysics National

Halogenated

Division

of Standards Colorado

and Technology 80303

PHYSICAL PROPERTIES EXECUTIVE This report is concerned rofluorcarbons

(CFCs)

with physical

SUMMARY

properties

used as refrigerants,

are the fixed points of the fluids (triple

of possible

solvents,

alternatives

and foam blowing

point and boiling

to the fully halogenated agents.

point temperatures,

Specifically and critical

chlo-

considered temperature,

pressure, and density), vapor pressure, saturated liquid density, solubility in water, and hydrolysis rates. These properties directly or indirectly influence the fate of a chemical in the environment and also include the key thermophysical

data necessary

containing

methanes

R123,

halogenated

R141b,

to estimate

and ethanes.

other properties.

Included

are R125,

The fluids considered

are hydrogen-

R22, R134a,

R124,

R152a,

R142b,

and methyl chloroform.

A wide variety of data sources have been considered

including

published data, surveys and compilations

of properties, and unpublished data provided by several of the companies which are members of the Alternative Fluorocarbon Environmental Acceptability Study (AFEAS) consortium. These data have been compiled and evaluated. Recommended values are tabulated for the fluid fixed points. The temperature dependencies of vapor pressure, saturated liquid density and solubility in pure water are presented lations and as a tabulation of values calculated from these correlations. The data vary greatly in quality and reliability,

and are sometimes

conflicting.

in terms of corre-

At least limited data were

available for the fixed points, vapor pressure and liquid density of all of the compounds. The values presented here are felt to be reasonable, although the lack of documentation in many cases makes an objective assessment of accuracy impossible, Identified

and revisions will certainly be necessary as additional data become available.

as high priority needs are improved

and improved

liquid density

For solubility

vapor pressure data for R 124, R142b, and, especially,

data for R142b.

in water, the data were much more limited.

able only for R22. For the other fluids,

unpublished

used; again, while these data may be reliable, bility information trapolating extremely

R141b,

was correlated

in terms

Published,

data provided

an assessment

of the Henry's

fully documented

by the chemical

of their accuracy law constant.

data were avail-

manufacturers

was not possible.

The use of Henry's

were

The solulaw in ex-

from the saturation vapor pressure conditions employed in most of the measurements to the low partial pressures that can be expected in the atmosphere is a source of uncertainty. For

solubility in salt water, only data for R22 and methyl chloroform were found; an empirical 'salting parameter' evaluated from data for these two fluids can be applied to the other fluids in the absence of data. Finally,

hydrolysis

decomposition

is considered.

of a compound

Hydrolysis

dissolved

represents

in the oceans

were quite sparse; except for R22 and methyl chloroform, In view of the very limited solubilities of these compounds, that can be estimated

or extrapolated

lution in water and subsequent

from the available

hydrolysis

one possible

mechanism

or in cloud water.

rates

recommended values could not be developed. even the order of magnitude-type information

data may be sufficient

is a significant

for the environmental

The data for hydrolysis

destruction

to determine

mechanism

whether

disso-

for these compounds.

Thus, complete data on solubility and hydrolysis may be needed only for methyl chloroform. This point is considered in detail in a study by Wine and Chameides presented elsewhere in this volume.

7 PRECEDING

PAGE BLALIK

NOT

FILM'ED

N92-15436

PHYSICAL

PROPERTIES

FULLY HALOGENATED

OF ALTERNATIVES

TO THE

CHLOROFLUOROCARBONS

Mark O. McLinden Thermophysics National

Institute

Division

of Standards

Boulder,

Colorado

and Technology 80303

PRECEDff'_G

PAGE

BLAD,_LKNOT

FILMED

PHYSICAL PROPERTIES 1. INTRODUCTION The physical

properties

of a fluid largely

determine

its suitability

present study is concerned

with properties

bons, a class of compounds

widely used as working fuids

equipment,

as solvents

and foam blowing

ples, the thermophysical and viscosity

properties

are necessary

conductivity

agents,

considered

environmental

of a fluid in refrigeration

agent has a large effect on the insulating

The

chlorofluorcar-

and air-conditioning As exam-

(PVT)

equipment.

behavior,

The thermal

value of a foam. The normal boiling

for solvent uses.

focuses on those properties point parameters),

in refrigeration

the pressure-volume-temperature

the performance

This paper, as part of the larger Alternative Specifically

to the fully halogenated

(refrigerants)

and in a wide variety of other applications.

such as enthalpy,

to predict

of the blowing

point is important

of possible alternatives

for use in a given application.

Fluorocarbon

that influence the environmental

acceptability

are the fluid fixed point parameters

vapor pressure,

implications

saturated

Environmental

of alternative

Study (AFEAS),

fluorocarbon

fluids.

(triple point, normal boiling point, and critical

liquid density,

of the first five properties

Assessment

solubility

in water, and hydrolysis

listed are indirect.

These properties

rates. The

are, however,

often required as inputs for various models and estimation techniques. The last two properties can directly affect the fate of a fluorocarbon once it is emitted to the environment. One possible mechanism for the removal

of a fluorocarbon

clouds and subsequent ic data associated ism is assessed

from the environment

reaction

The fluids to be considered

literature

to replace

compilations by several

over information

the fully halogenated

halogenated

thus, all possible

sources

such as that by the Japanese chemical

manufacturers

produced

methanes

and

seen with

given to published

Association

presented

graphically

of Refrigeration of the AFEAS

sources

or in terms of a correlation.

and, as will be seen, are sometimes

These include

and surveys such as that by Stewart,

which are members

over unpublished

and as a consequence,

of data have been utilized.

Abstracts

work in progress at the National Institute of Standards and Technology is generally

the bas-

of this mechan-

fluids is similar to the range

here have never been commercially

(as revealed by a search of Chemical

data provided

reliability

This paper addresses the effectiveness

in

compounds.

et al. (1981)),

preference

candidates

boiling points for these candidate

the data for many of them are sparse;

experimental

or in water droplets

(1989).

in this report are the leading

In many cases, the fluids considered the published

in the environment;

and R11 (CC13F). All are hydrogen-containing

The range of normal

the fully halogenated

in the ocean

with water (hydrolysis).

of decomposition

by Wine and Chameides

CFCs such as R12 (CClzFz) ethanes.

of the fluorocarbon

with this mechanism

is its dissolution

(1975),

unpublished

group, and, finally,

(NIST). Where available,

and to actual experimental

The data differ greatly

values

in quality and

conflicting.

To be of maximum and immediate utility to the other AFEAS groups which may need to make use of this information, all data are fit with standard forms and presented primarily in terms of the resulting correlations. In this report a summary section containing a detailed discussion of the data themselves.

coefficients

to the correlations,

11

RE-CEDING

PAGE

BI.AE_IK NOT

F_LMI_D

etc. precedes

PHYSICAL PROPERTIES 2. SUMMARY Fluid Fixed Points The triple point, normal

boiling point, and critical point parameters

are fundamental

characteristics

of

a fluid. The triple point is the state at which three phases (solid, liquid and vapor) coexist; it is virtually identical with the more often reported freezing point. The normal boiling point is simply the temperature at which the vapor pressure of a fluid is one standard atmosphere (101.325 kPa). Since the vapor pressures of nearly all fluids are approximately parallel when plotted as the logarithm of pressure versus inverse temperature, the normal boiling point is a rough predictor of the vapor pressure at all temperatures. The critical point is the state at which the properties of the saturated liquid and vapor become indistinguishable;

coexisting

liquid and vapor are possible

only at temperatures

and pressures

below the critical

point values. These parameters, many different

often in the absence of any other information,

compounds

are frequently

to select a more limited set for further study.

used in screening among

For many applications

they de-

fine the temperature limits for the use of a particular fluid. Clearly a solvent or refrigerant cannot be used below the triple point temperature. For many refrigeration applications, operation at sub-atmospheric pressures is avoided and, thus, the normal boiling point is a more practical lower limit. Vapor compression refrigeration

equipment

transports

heat through

condensation

and evaporation

(i.e. two-phase)

processes

and thus the critical point represents an upper temperature and pressure limit. The critical point parameters are the essential inputs to estimation techniques based on the law of corresponding states, which is the observation

that, when scaled by the critical

parameters,

The triple point, normal boiling point, and critical

the properties

point parameters

of nearly all fluids are similar.

are given in Table 1. (In this table,

and all subsequent tables, the fluids are listed in order of increasing normal boiling The selection of these values is discussed in detail in the Discussion section.

Vapor

point temperature.)

Pressure

The experimental a form suggested

vapor pressure by Goodwin

data were fit to the following

& Haynes

In p = at/T where p is pressure, asymptotic

critical

T is absolute behavior

which

is a modification

of

(1982): + a2 + a3T +

temperature

(kelvins)

was empirically

range for R134a and R123 (Weber

1989). The coefficients

a4(l-

T/Tc)1"5

(1)

and T c is the critical

predict a value of approximately

tion (1); a value of 1.5, however, the temperature

equation,

temperature.

1.9 for the exponent

found to yield a better

for

in the last term in Equa-

fit over a wide temperature

for each of the fluids considered,

range of the data, are given in Table 2. Modest

Theories

extrapolations

along with

outside this range should

yield fairly accurate results. This table also gives the RMS deviations between Equation (1) and the input data. These RMS values serve as indications of the precision of the data and the agreement between different sources.

Particularly

for those fluids with only one data source, the method of computing

tions cannot detect any systematic

errors

in the data, and thus RMS values 12

provide

RMS devia-

little information

on

PHYSICAL PROPERTIES the accuracy of the data and the resulting correlation. In most cases the accuracy of the correlation cannot be stated because of insufficient documentation; this is considered in more detail in the Discussion section. The vapor pressures

as functions

of temperature

are also tabulated

along with the other properties

in the Appendix.

Saturated

Liquid Density

Liquid densities

along the saturation

line, Q, were fit to the commonly

O/Oc = 1 + dlr0 where r = (1 - T/T c and 0c is the critical

used form:

+ d2"r2/3 + d3r + d4v4/3

density.

The critical

(2)

exponent,/3,

is properly

evaluated

from

experimental measurements near the critical point. For most of the fluids considered here a value of 1/3 is assumed because of the lack of data. Equation (2) is well-grounded in theory, has the proper form over a wide range of temperature of saturated

liquid densities.

vapor pressure, perature

the vicinity of the critical point, and is often used in the correlation

The fit of density data to Equation

the temperature

and density

Solubility

including

required

(2) is summarized

range of the data and the RMS deviation in Equation

(2) may be found

in Table

in Table 3. As with

are also given. The critical

tem-

1.

in Water

The fluids considered typical ambient

in this report are all highly volatile

temperatures)

and thus their presence

(most have normal boiling points well below

in the environment

will be predominantly

as trace

gases in the atmosphere. Atmospheric gases will, however, dissolve to some extent into the oceans and into water droplets in clouds. The magnitude of this solubility will influence the importance of hydrolysis as a degradation

mechanism.

The dissolution

of trace gases into water is well-represented Xa

which states that the concentration tial pressure

of substance

approaching

zero but in practice

"a"

of substance

"a"

dissolved

in a solvent,

Pa" Henry's

Xa, is proportional

to the par-

law strictly applies only in the limit of xa

holds very well for gas partial

even higher for gases of low solubility

law: (3)

Pa/Ha

=

over the solution,

by Henry's

pressures

(such as the fluorocarbons).

up to a few hundred

The proportionality

kPa and

factor in Equation

is called the Henry's law constant. The units of H a are pressure divided by a concentration (e.g. kPa/mass % or atm/ppm). The Henry's law constant is not constant but is a function of temperature which (3),

H a,

can be well represented

by: In (1/Ha)

= ht + hz/(T

+

(4)

h3)

Solubility data have been used to evaluate the coefficients in Equation 4; they are given in Table 4. Note that the term h3 is used only for R22. Equation 4 has been used to calculate solubilities in water at the commonly

referenced

conditions

of 298.15

K (25°C) and a fluorocarbon

partial

pressure

of one

standard atmosphere. (While this is an unrealistically large partial pressure for gases in the environment, it is useful for comparisons between compounds.) For several of the fluids there was considerable disagreement

(as much as a factor of two) in measured

by comments

solubility

in Table 4. 13

from different

sources;

these are flagged

PHYSICAL PROPERTIES At least limited

solubility

pounds considered

data were obtained

as part of AFEAS.

not exist, the method of Irmann solubilities pressure

of the halogenated at 298.15

(mostly

from unpublished

sources)

For other fluids which may be of interest

(1965) (as reported

hydrocarbons.

by Lyman,

et al. 1982) can be used to estimate

This method requires

K (25°C) of the compound

in question

for all of the com-

and for which data may

only the molecular

and yields the solubility

structure

the

and vapor

in water at 298.15

K.

The results of applying this estimation technique to the nine compounds considered here are given in Table 5. For most of the fluids the agreement is very good (within 15 %), validating this method. The estimated values for R 125 and R 14 l b, however, values. In view of the good agreement values

for R125 and certainly

for the other fluids, this discrepancy

from the reported

casts some doubt on the reported

for R141b.

The above results are for solubilities ed by the following

differ by factors of two and five, respectively

form reported

in pure water. The solubilities

by Lyman, In

in saline solutions

can be represent-

et al. (1982):

(Xa/Xa,s)

--

(5)

KsC s

x a is the solubility in pure water and Xa, s is the solubility in a saline solution of concentration C s. The term Ks is an empirical salting parameter. Values of K s are positive, so solubilities in salt water are where

lower than those in pure water. methyl chloroform.

Zhang,

For the compounds

of interest

et al. (1985) report R22 solubilities

here, data were found only for R22 and in sodium chloride

solutions

over the tem-

perature range 283-323 K. Their data confirm Equation (5) and can be used to compute values of K s ranging from 0.0060 L/g at 283 K to 0.0082 L/g at 333 K. These correspond to solubilities in sea water which are 81-75%

of those in pure water.

for methyl chloroform Limited

corresponding

data for the solubility

Walraevens,

et al. (1974) report a salting parameter

to a solubility

in sea water

of other fluorocarbons

(CHCI2F) (Downing 1988) and R114 (CCIF2CC1F2) 0.0061 and 0.029 L/g respectively; these correspond

which

with other classes

and methyl chloroform fully halogenated

R114.

of fluids (Lyman,

are better analogues

in salt solutions

were also found.

et al. 1982). The polar,

to the full set of fluids considered

The effect of salt on the solubilities

for the other fluids in the absence

Data for R21

is similar to those

hydrogen-containing

of data. This corresponds

R22, R21,

here than the weakly polar,

of the fluids considered

in this report

thus, probably closer to those observed with R22 and R21 than with R114. Considering of salting parameters for R22, R21, and methyl chloroform, a salting parameter of 0.007 mended

L/g

(Stepakoff and Modica 1973) give values of Ks of to solubilities in sea water which are 81 and 36%

of those in pure water. This range for the ratio of sea water to pure water solubilities observed

of 0.0073

is 78% of that in pure water.

to a solubility

is,

the similarity L/g is recom-

in sea water which

is 78% of that in pure water.

Hydrolysis Hydrolysis

Rates refers to the reaction of a compound

isms are possible fluorocarbon

(Ellenrieder

reacts

and Reinhard

with water or the hydroxide R-C-R'X

in aqueous solution. For the fluorocarbons,

1988). In nucleophilic

+ H20/OH-

ion (OH-) _ 14

substitution,

to form an alcohol

R-C-R'OH

+ HX

two mechan-

or hydrolysis

proper,

the

plus an acid: (6)

PHYSICAL PROPERTIES where X represents a halogen (F or CI) and R and R' are nonreacting groups. In the second mechanism, known as elimination or dehydrohalogenation, water or hydroxide catalyzes the reaction to form an alkene plus acid: R-CH-CR'X

+ HzO/OH-_

RC=CR'

+ H20/OH-

(7)

+ HX

In this work, the term "hydrolysis" will refer to the general reaction in aqueous solution; the terms "substitution" and "elimination" will be used when it is necessary to distinguish between the different mechanisms.

A single-carbon

Other mechanisms here.

compound

(such as R22) can obviously

occur for the fully halogenated

The elimination

increases (reaction

with hydroxyl).

more important

process.

1988) but will not be considered

in the molecule

(Mabey

becomes

undergo only the substitution

(Downing

(Vogel, et al. 1987). Either process may be neutral (reaction primarily with water) or base-promoted primarily

process

compounds

A third possibility,

as the number of halogens

acid promotion

by the hydronium

ion, H +, does not occur

and Mill 1978).

The rate of reaction, fluorocarbon

expressed

concentration.

rates. For base-promoted

in terms

of the disappearance

Thus the solubility processes,

the reaction

case of base-promoted

can be expressed

and neutral

process

is proportional

will have an influence

rate is also proportional

which in turn is related to the pH. Where the neutral For the general

of fluorocarbon,

of the compound

dominates,

processes

occurring

= [RX](kB[OH-]

+ k N)

to the hydroxyl

concentration,

the rate is independent simultaneously,

where square brackets

denote a concentration

in moles/liter,

the reaction

of the rate constants

are functions

of temperature,

typically

expressed

fluorocarbon,

and kB and

respectively. Both kB and kN may and elimination mechanisms. Each in terms of an Arrhenius

expression:

k = A exp(-E/RT) E is the activation

energy

of a fluorocarbon

isms. To fully describe To further complicate

of the reaction

is thus seen to be a rather complex process with several possible mechan-

the temperature the situation,

1988 gives information

and pH dependence

dependence

of a reaction

metals can catalyze hydrolysis

and pH dependence

= k[R22][OH-]

of k is given by Equation

15

requires

(9) with:

up to eight parameters.

and increase reaction

located for the hydrolysis

on both the temperature -d[R22]/dt

The temperature

(9)

and R is the gas constant.

of magnitude or more (Downing 1988). The information bons considered here was limited. Downing

rate

(8)

RX is the reacting

k N are the rate constants for the base-promoted and neutral processes, be further broken down into additive contributions from the substitution

The hydrolysis

of pH.

as: -d[RX]/dt

where

to the

on its reaction

rates by an order

rates of the fluorocar-

of R22 hydrolysis

rates: (10)

PHYSICAL PROPERTIES A = 1.87 x 108 L/(mol's) -E/R One must infer from Equation together

(10) that either the neutral

into a single rate constant

At a temperature

= -7692.

or that the former

of 298 K and a concentration

K

and base-promoted process

of hydroxide

processes

is insignificant,

have been lumped

i.e. kN is small.

of 1 x 10-7 mol/L (corresponding

to pure

water of pH = 7) the above expression yields an overall rate constant (i.e. kB[OH- ] + kN) of 1.15 x 10-_° s-_; at an R22 concentration of 0.033 mol/L (the solubility of R22 at a partial pressure of 101.3 kPa) the corresponding

hydrolysis

value of 4.5 x 10 -12 mol/(L.s) Ellenreider

and Reinhard

rate is 3.8 x 10 -12 mol/(L.s).

given by DuPont

(1989)

(I 988) have developed

This is in reasonable

agreement

with the

at the same conditions.

an interactive,

computerized

data base for the calcula-

tion of hydrolysis rates as functions of temperature and pH. While this would be an ideal method of presenting hydrolysis

data, of the compounds

of interest

here, only methyl chloroform

is presently

included

in this

data base. In the paper by Ellenreider and Reinhard, methyl chloroform is presented as an example. At 293 K in pure water (pH = 7) the rate constant for the substitution reaction is 8.1 x 10 -9 s-1 with the neutral process dominant

by several orders of magnitude

over the base-promoted

process;

for the elimina-

tion mechanism the rate constant is 2.0 x 10 -9 s-I for the neutral process (no data are given for the basepromoted elimination process). The overall rate constant is 1.0 x 10 -8 s-_. For a concentration of 0.033 mol/L

(the saturation

The temperature expressed

concentration

dependence

in terms

of methyl chloroform)

is also given by Ellenreider

of Equation

the hydrolysis and Reinhard.

rate is 3.3 x 10 -l° mol/(L's). The overall

rate constant

can be

(9) with: A = 1.28 x 1013 s-_ -E/R

This implies that the hydrolysis Perhaps

a more convenient

life of the reacting

reaction

= -14244.

is a factor of five faster at 303 K than at a temperature

means of expressing

species. The half-life

K

the rate of a first order reaction

is independent

of reactant composition.

of 293 K.

is in terms of the half-

Ellenreider

and Reinhard

report a half-life of 0.96 year for methyl chloroform at 298 K and pH = 7. The hydrolysis rate constant for R22 yields a half-life of 191 years at the same conditions. Thus, there is a vast difference in the effectiveness

of hydrolysis

in breaking

down

a compound

in the environment.

For R123, DuPont (1989) reports a hydrolysis rate approximately 4.3 times that for R22 for a test of 100 days at 328 K. A series of 3-day tests at 358 K indicated that R141b is less stable than R123 but considerably

more stable than methyl chloroform.

In these short-term

test the amount

of decomposition

was less than 5 ppm for R123 and R141b and 0.006% for methly chloroform. "Stability" data of Allied (1989), however, report that the production of acid from R123 in aqueous solution is 38% of that with R22. The Allied information also indicates that the acid production rates with R124 and R142b are, respectively, 1.35 and 1.65 times that observed with R22. The Allied data are for tests at 314 K and result from measurements the DuPont

of the decomposition and Allied results

of fluorocarbon

suggest caution

over a period

of three months.

in the use of any hydrolysis 16

rate data.

The differences

in

PHYSICAL PROPERTIES

The database

of Ellenreider

and Reinhard,

along with a survey by Mabey

and Mill (1978), unfortunate-

ly, do not contain information on any of the other compounds of interest here. In general terms, chlorine is much more reactive than fluorine (Hine, et al. 1961) so the chlorine-free compounds (R125, R134a, R152a) will probably have lower hydrolysis rates than those reported for R22 or R123. The data for the relative reaction rates of R22, R142b, R124, R123, and Rl41b suggest that the hydrolysis rates for all of these chloroflouro dered here, others

compounds

will be of the same order of magnitude.

only methyl chloroform

will likely have half-lives

is likely to have a hydrolytic

on the order

of a century

Thus, for the nine fluids consi-

half-life

on the order of a year;

all the

or more.

3. DISCUSSION R125 The data for R 125 (pentafluoroethane) cal temperature of these values The saturated

are limited.

Both Allied (1989) and DuPont

liquid density and vapor pressure

liquid density value and graphical

presentation

data reported

by Allied were selected

of vapor pressure

given by DuPont

cients to Equations (1) and (2). A comparison of these data with the correlations 1. The critical pressure (reported in Table 1) was calculated by an extrapolation

Table

Fluid

(1989) report a criti-

of 339.4 K. DuPont also gives a freezing point temperature and critical density. are documented, but they are adopted here in the absence of any other data.

Chemical formula

None

over the single

in fitting the coeffiis presented of Equation

in Figure (1) to the

1. Fluid Fixed Points

Mol.

Tr. Pt.

Norm.

Boiling

Pt.

Critical

Point

mass

temp.

temp.

liq. den.

temp.

pres.

density

(g/mol)

(K)

(K)

(kg/m 3)

(K)

(kPa)

(kg/m 3)

R125

CF3CHF2

120.020

170.

224.6

1515.

339.4

3631.

571.5

R22

CHC1F2

86.468

113.

232.4

1409.

369.30

4990.

513.0

R134a

CF3CH2F

102.030

172.

247.1

1373.

374.21

4056.

515.3

R152a

CHF2CH3

66.050

156.

249.0

1011.

386.44

4520.

368.0

R124

CHC1FCF3

136.475

74.

261.2

1472.

395.65

3640.

560.0

R142b

CH3CCIF2

100.495

142.

264.0

1193.

410.25

4246.

435.0

R123

CHCI2CF3

152.930

166.

301.0

1456.

456.94

3674.

549.9

R141b

CH3CC12F

116.950

170.

305.3

1216.

481.5

4540.

464.1

methyl chlr.

CH3CC13

133.405

243.

347.3

1250.

545.

4300.

470.0

*Note: None of the critical densities are known to four significant figures; they are given to this level for consistency with Eqn (2). 17

PHYSICAL

PROPERTIES ,

('d

I

,

I

i

I

,

TO

o t'-_k

a. A

O

Q. =

t,-

i



Allied

data

T c X

200

r

240

280 Temperature

,

(N

F

I

,

320

360

(K) I

t--

o o

C_ "" A

O

C_ i u

Q; v



Allied

data

iTc

N

200

24'0

280 Temperature

Figure

1, Comparison

of correlations

with

data

for

density.

18

R125;

3;20

360

(K)

a) vapor

pressure;

b) saturated

liquid

PHYSICAL PROPERTIES

critical temperature (1989).

(an extrapolation

of only 6.3 K) rather than the value of 3520 kPa reported

As with all the fluids in this report,

obtained

by finding the temperature

(101.325

the normal

boiling point temperature

at which Equation

(1) yields a pressure

in Table

of one standard

1 is

atmosphere

kPa).

The eight liquid densities K using glass flotation

reported

by Allied were measured

beads of known density.

over the temperature

In this technique,

the temperature

so that the density of the fluid matches that of one of the beads. In another son and Basu 1988), the accuracy apparently

reported

by DuPont,

not corrected

of [his method

for the effects

is claimed

of temperature

range 228.7-336.3

of the fluid is adjusted

work by the same group (Wil-

to be 0.2 kg/m 3. The values

on the densities

for R125 were

of the glass beads.

Judging

by

other results by this method, these corrections should be less than 0.1 kg/m 3 for the temperature range of the measurements for R125. The excellent fit of Equation (2) to within 6 K of the critical temperature gives

some credence

to the critical

The only information tion (4) reported

on solubility

by DuPont

(1989).

density

of DuPont

used in the correlation.

in water were coefficients The experimental

technique

malee (1953). No data were given but an "experimental coefficients

are reported

to a correlation

was similar to that employed

data range"

in Table 4 after the appropriate

similar in form to Equa-

conversion

of 298-333

K was indicated.

by ParThese

of units.

R22 The extensive

body of data on R22 (chlorodifluoromethane)

in the treatise by the Japanese

Association

of Refrigeration

Table 2. Vapor

Fluid

is summarized,

evaluated,

and correlated

(1975). Although additional data have been meas-

Pressure

Temperature low (K)

limits high (K)

a_

Coefficients to Equation (1) a2 a_ (p in kPa, T in K)

a4

RMS error (%)

R125

233.

Tc

-2678.571

16.63306

-0.001602304

1.390420

0.12

R22

223.

Tc

-2907.443

17.05244

-0.001796055

2.204052

0.09

R134a

210.

Tc

-3353.464

18.36056

-0.002908044

2.783663

0.19

R152a

273.

Tc

-3110.511

17.02405

-0.001445740

2.105154

0.05

R124

222.

Tc

-3471.946

18.16083

-0.002997217

2.703744

0.35

R142b

233.

369.

-3382.422

17.01384

-0.001012149

3.224924

0.30

R123

243.

Tc

-4060.080

18.20783

-0.002426370

3.164297

0.17

R141b

243.

475.

-4388.810

18.40668

-0.001808752

5.149630

2.20

methyl chlr.

295.

371.

-4809.873

17.93429

-0.001362322

4.617096

0.02

19

PHYSICAL

PROPERTIES

TABULATED VALUES OF VAPOR PRESSURE, LIQUID DENSITY AND SOLUBILITY IN WATER Properties (Parentheses

Temp.

of R125 indicate

Properties

extrapolation

Vapor Pressure

of

Sat.

data)

Liq.

(Parentheses

Henry's

const.

of R22 indicate

Temp.

Density

extrapolation

of

data)

Vapor

Sat.

Liq.

(oC)

(kPa)

(°C)

Pressure (kPa)

-40.0

150.6

1484.0

-40.0

105.3

1406.5

186.9

-35.0

(kg/m

J)

(kPa/Mass%)

Density (kg/m 3)

1465.4

-35.0

132.0

1391.8

-30.0

229.8

1446.3

-30.0

163.8

1376.9

-25.0 -20.0

280.1 338.5

1426.8 1406.8

-25.0

201.2

1361.8

-20.0

245.1

1346.4

- 15.0

406.0

1386.2

-15.0

295.9

1330.6

-10.0

483.3

1365.0

-10.0

354.5

1314.6

-5.0

571.4

1343.1

0.0

671.2

1320.4

(

242.)

-5,0 0.0

421.6 498.0

1298.2 1281.5

5.0

783.7

1296.8

I

331.)

10.0 15.0

909.8 1050.7

1272.2 1246.4

( (

448.) 599.)

5.0 10.0

584.3 681.3

1264.3 1246.7

20.0

1207.2

1219.3

(

794.)

25.0 30,0

1380.6 1571.9

1190.4 1159.6

Henry's

const.

(kPa/Mass

82.)

15.0

789.9

1228.6

1223 171. 227.

20.0

910.8

1210.0

288.

1042. 1355.

25.0

1044.9

1190.7

354.

30.0

1193.1

1170.8

425.

35.0

1782.4

1126.2

1747.

2013.4

1089.7

2234.

35.0 40.0

1356.1 1534.8

1150.1 1128.6

498.

40.0 45.0

2266.2

1048.8

2835.

45.0

1730.3

1106.0

50.0

2542.5

1001.8

3572.

50.0

1943.4

1082.3

650. 727.

55.0

2844.1

945.3

4469.

55.0

2175.3

1057.1

805.

60.0 65.0

3173.5 3534.4

870.5 735.8

(5553.) (6857.)

60.0

2427.1

1030.3

883.

65.0

2700.0

1001.3

961.

70.0

2995,4

969.7

1038.

75.0

3315.1

934.4

1114.

80.0 85.0

3660.8 4035.1

893.9 845.2

1189.) 1263.)

90.0

4441.6

780.6

95.0

4886.2

660.9

1336.) 1408.)

NBP:-48.6

(101.3)

(1515.2)

Tc:

(3630.6)

(571.5)

66.3

NBP: Tc:

20

-40.8

101.3

(1408.9)

96.2

(4995.6)

( 513.0)

573.

_)

PHYSICAL PROPERTIES ured since the publication of this work, the recommendations limited time available for this project could be better expended

of the JAR were adopted here so that the on other fluids for which no such compila-

tions exist. The triple

point and critical

point values

were fit by the JAR based largely

of the JAR are adopted

on the data of Zander

here.

The saturated-liquid

densities

(1968) to the same form used here (Equation

(2)) and thus the coefficients given in Table 3 are those reported by the JAR. This correlation from 204 K to the critical temperature with an RMS deviation of approximately 0.1%.

is valid

The vapor pressure data of Kletskii (1964), Kohlen (1985), and Zander (1968) were fit to Equation (1); the residuals are shown in Figure 2. The three lowest temperature (203.3-211.3 K) points of Zander and his point at 366.1 K were excluded from the fit. The high temperature

point appeared

to be anomalously

high compared to the other data sets while the three low temperature points could not be fit without seriously affecting the correlation at higher temperatures. (In Figure 2 and all similar residual plots, points used in the correlation are shown as filled-in symbols; points excluded from the fit are shown as open symbols.) R22 solubility data are reported by Parmelee (1953). Fourteen data points at three temperatures were measured with an estimated accuracy of 5 % using a gas volumetric technique. Parmelee correlated his data to a form similar to Equation conversion

(4) and his coefficients

are reported

in Table 4 after the appropriate

of units. ¢N

Q O o

el

•If"

O



.. "

'

"'"

¢D

el i

_o el m,i

• data of Kletskii • data of Zander • data of Kohlen i

200

240

!Tc i

i

T

280

320

360

400

Temperature (K) Figure 2. Comparison of vapor pressure correlation with data for R22; filled-in and open symbols indicate points used and not used, respectively, in fitting correlation. 21

PHYSICAL PROPERTIES R134a Refrigerant property

134a (1, l,l,2-tetrafluoroethane)

community

measured

recently,

has been the focus of considerable

and considerable

data have become

available.

by Kabata, et al. (1988), Wilson and Basu (1988), and Morrison

tion, carried agreement.

out at NIST, DuPont

Two reliable

is adopted

(1989)

sources

here,

and Daikin

of vapor

although

pressure

data are available;

from 211.0 K to within 1 K of the critical temperature. ed accuracy

parameters

temperatures

together

et al. (1988)

K. Unfortunately,

presented

Weber (1989) measured

have measured

reported by three independent groups. wide range of temperature (238.9-371.6 six measurements 268.2-368.2

in the vicinity

the vapor pressure

in fitting Equation

(2); the residuals

a vibrating tube densimeter are in reasonable agreement,

points. Saturated

range

22 values with an estimatof 0.7-7.

kPa (depend-

over the temperature

in McLinden,

of R134a at 25 temperatures

point.

Morrison

mercury-displacement are shown in Figure

were not available although differences

et al. (1989). from 253-371

liquid densities

have been

(1989)

apparatus. 3. (Further

has measured

11 values

from

These three data sets were used measurements

by Morrison

using

in time to include in this work.) The different data sets of as much as 1.5 % exist, especially near the critical point.

of R134a in water has been measured

points were read off their graphical

are in excellent

Wilson and Basu (1988) report nine measurements over a fairly K) using the floating bead technique. Kabata, et al. (1988) report

of the critical

K with a variable-volume,

The solubility

here is identical with that presented

their paper does not give the experimental

determina-

of 172 K.

As shown in Figure 3, the two data sets are in excellent agreement

range of overlap. The correlation

point has been

they span the temperature

of 0.2 kPa. Wilson and Basu (1988) report 32 values with an accuracy

ing on the pressure). Yamashita,

The critical

in the fluid

(1989). Morrison's

all three sets of critical

(1989) both report freezing

attention

presentation

by DuPont

(1989)

at 298 and 353 K. These two

and used to fit the coefficients

in Equation

(4).

R152a The primary

source of data for R152a (1,1-difluoroethane)

was the work of Higashi,

et al. (1987). Their

critical point determination is consistent with the earlier determination by Mears, et al. (1955), which is the basis of the critical parameters listed on many manufacturer's data sheets. The determination by Higashi, et al. is, however, of much higher accuracy (0.01 K for temperature, 1.0 kPa for pressure, and 2 kg/m 3 for density) and is adopted here. The freezing point reported by DuPont (1989) is used here. Higashi,

et al. report 44 vapor pressure

measurements

from 273.1

K to within 0.4 K of the critical

temperature temperature

with a precision better than 0.17%. Additional data, of lower accuracy but covering a wider range (203.7 K and above), are reported by Mears, et al. The data sets of Higashi, et al.

and Mears,

et al. are in reasonable

agreement

above 290 K but diverge rapidly

see Figure 4. (In Figure 4 and all similar figures, residuals

greater

of Equation

points drawn just outside the frame of the plot indicate

than the limits of the ordinate and are not to scale.)

(1) to lower temperatures

a much poorer

fit at the higher

All attempts

by including selected low temperature

temperatures.

at lower temperatures;

The accuracy

to extend

the range

points of Mears resulted in

of the data by Mears,

et al. is difficult to

ascertain but is probably no better than 5-10 kPa; this uncertainty would be equivalent to an error of as much as 10% at the lowest temperatures. Thus, only the vapor pressure data of Higashi, et al. were used in fitting Equation

(1). 22

PHYSICAL

PROPERTIES

i

(N

t-Q 0 Mk



O. A

• mm

'_,_

0

=



o .,_mr

Q. 0 c_ a. v 'T,

• data • data

of Weber of Wilson

& Basu

T c

(N i

200

240

r

280

i

J

360

320

Temperature i

[

_

400

(K)

=

i

L

J

n

Q Q

O;

• •



:

• m:

• •

• m:

i _u

i

• data of Wilson • data of Kabata •

data

& Basu et al.

of Morrison

iT c

N

200

240

280

320

Temperature

Figure 3. Comparison density.

of correlations

with

data for R134a;

23

360

400

(K)

a) vapor

pressure;

b) saturated

liquid

PHYSICAL

Properties (Parentheses

Temp. (°C)

Properties

of R134a indicate

extrapolation

Vapor Pressure (kPa)

of

(Parentheses

data)

Sat. Liq. Density (kg/m

3)

Henry's

Temp.

const.

of R152a indicate

extrapolation

Vapor Pressure

(kPa/Mass%)

('C)

(kPa)

of

data)

Sat.

Liq.

Henry's

const.

Density (kg/m

3)

(kPa/Mass%)

-40.0

51.6

(1413.51

-40.0

-35.0

66.5

(1399.2)

-35.0

-30.0 -25.0

84.7 106.6

1384.6 1369.8

-30.0 -25.0

97,6)

1013.0

-20.0 -15.0

132.9 164,1

1354.8 1339.5

-20.0 -15.0

121.2)

1002.6

149.0)

992. l

-10.0

200.7

1324.0

-10.0

181.8)

981.3

-5.0

243.4

1308.2

-5.0

0.0

292.9

1292.1

3O2.)

0.0

219.9) 263.9

970.3 959.1

178.

5.0

349.8

1275.7

359.)

5.0

314.6

947.7

207.

10.0

414.8

1258.8

425.)

10.0

15.0 20.0

488.7 572.1

1241.5 1223.8

499.)

15.0

372.5 438.2

936.0 924.0

239. 275.

665.8 770.7

1205.5 1186.7

583.) 678.

20.0 25.0

512.5 596.0

911.7 899.0

316.

25.0 30.0

784.

30.0

689.4

886.0

409.

35.0

887.4

1167.1

35.0

793.4

872.6

462.

40.0

1017.0

1146.8

903. 1035.

40.0

908.9

858.8

521.

45.0

1160.1

1125.7

1181.

45.0

1036.5

844.5

584.

5(I.0

1317.8

1103.4

1342.

50.0

55.0

1491.0

1080.0

1520.

55.0

1177.1 1331.5

829.7 814.2

654. 729.

60.0

1680.7

1055.1

1714.

60.0

1500.5

798.1

809.

65.0 70.0

1888.2 2114.6

1028.5 999.6

1927.

1685.1 1886.2

781.1 763.2

896.

2158.

65.0 70.0

75.0

2361.5

967.9

2409.

75.0

2104.8

744.2

(1o9o.)

80.0

2630.4

932.4

2682.)

80.0

2342.1

723.9

(1197.)

85.0

2923.4

891.4

2976.)

85.0

2599.3

701.8

(131o.)

90.0

3243.1

841.7

3293.)

90.0

2877.9

677.5

95.0

3593.0

775.3

3634.)

95.0

3179.4

650.1

(1432.) (1560.)

100,0

3979.6

650.9

3999.)

100.0

3505.8

618.1

(1696.)

-24.2 113.3

101.3

1011.2

4519.8

368.0

NBP:-26.1 Tc:

PROPERTIES

101.1

101.3 4067.9

NBP:

1373.1

Tc:

515.3

24

48.0)

1043.0

61.5) 77.9)

1033.2 1023.1

360.

990.

PHYSICAL PROPERTIES ,

(N

I

i

J

,

,

I

,

I

0

o data of Mears et al. • data of Higashi

qe-

0 0 y_

,

E E .J

m

°--

e-

Q

?

e-

E o

L.)I 'q 'tuJe; fSJeu9 uo!_.ehp,:)V 0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

-z_ _/

0 0 0

"_

_ e-

E .--

q r,,

O

E

"-

EE

o CD

q Q; '_

mx::

d E .-J 0

E i

o tN

0

If) 0

143

cO

?

"t-

_

"_

TROPOSPHERIC LIFETIMES

At the end of the 100 year model experiment, total halocarbon

injection

rate to determine

the total model halocarbon

the halocarbon

lifetime.

hydroxyl radical concentrations implies low tropospheric tropospheric hydroxyl radical concentrations. For reactive centrations

inventory

The assumption

was divided

by the

of fixed tropospheric

halocarbon loadings so as not to perturb the halocarbons, this implies that halocarbon con-

are not more than 1 ppb at the most.

Figure 8 shows the total lifetimes including both tropospheric OH oxidation and stratospheric removal calculated for various assumptions concerning the form of the temperature dependent OH + halocarbon rate coefficient. lifetime, factors

Clearly,

this temperature

with lifetimes

covering

and activation

However

parameter

exerts a dominant

0.2 - 30 years for reasonable

ranges in expected

influence

on halocarbon

values of preexponential

energies.

the _4CO method is not uncertainty-free

mining halocarbon sumptions

dependent

lifetime

is dependent

and its accuracy

and precision

on a whole range of experimental,

which may be called into question.

Volz, Ehhalt and Derwent

as a means

of deter-

life cycle and modelling (1981)

as-

gave some thought

to

uncertainty limits on their tropospheric OH distribution which this reevaluation has not changed. They recommended a mean tropospheric OH concentration of 6.5 +_3 molecule cm -3. Assuming that the kinetic parameters

defining

the OH

+ halocarbon

rate coefficient

are described

with complete

certainty,

we

can use the 1-sigma confidence limits for the tropospheric OH distribution to determine the confidence limits of the halocarbon lifetime. The Harwell two-dimensional model was therefore rerun with the entire tropospheric

OH distribution

ing upper and lower

scaled upwards

1-sigma confidence

factor of two for all the halocarbons

examined.

mined for the longer-lived

halocarbons,

Lifetimes

Fluorocarbons

of Alternative

and downwards

For some of the candidate alternative

to the 1-sigma confidence

limits of the halocarbon Lifetimes

lifetimes

were apparently

limits. The result-

encompassed

the range of a

slightly more accurately

reflecting the influence of the assumed constant stratospheric

fluorocarbons

deter-

removal.

evaluated chemical kinetic data for the OH + halocar-

bon degradation reactions are already available, Table 2. The lifetimes of these halocarbons due to stratospheric removal and tropospheric OH radical degradation can therefore be determined using the Harwell two-dimensional

model. Table 2 gives the atmospheric

latitudes of the northern

hemisphere

lifetimes

calculated

from a 100 year model calculation.

for a constant

The tropospheric

injection

in mid-

OH distribution

calculated with the _4CO method gives lifetimes for the alternative fluorocarbons in the range 0.3-635 years. For most of the alternative halocarbons, these lifetimes are considerably shorter than the corresponding lifetimes

for the fully halogenated

To complete

the environmental

haviour of any chlorine-containing haviour

of the fragments

halocarbons. acceptability molecular

work, modelling fragments

could readily be incorporated

magnitude of any CFCI2CO(O2)NO2,

stratospheric CF2CICHO,

chlorine-containing

fragments

produced

studies are required

following

by the halocarbon

degradation.

into the two-dimensional

up the beThe be-

model to determine

the

fluxes of species such as COC12, COHC1, CF3COCI, CFC12CHO, CF2C1CO(O2)NO2, COFC1 and so on. Competing processes for these

would include tropospheric

scavenging. 144

degradation,

dry deposition,

photolysis

and wet

TROPOSPHERIC LIFETIMES

Table

2.

OH

+ halocarbon

rate coefficients

and atmospheric

lifetimes

for a range

of alternative

fluorocarbons Lifetime, c OH Formulae

+ halocarbon rate coefficient, cm 3 molecule-i s-_

yrs Stratospheric loss

None

CH3F

5.4 x 10 -lz exp(-1700/T)

3.12

3.33

CHzFz

2.5 x 10 -lz exp(-1650/T)

5.40

6.0

CHF3

7.4 x 10 -13 exp(-2350/T)

46.35

635.0

CHzFCI

3.0 x 10-12 exp(-1250/T)

1.23

1.26

CHFC12

1.2 x 10 -_2 exp(-I IO0/T)

1.74

.80

CHF2CI

1.2 x 10 -12 exp(-1650/T)

10.35

13.0

CH3CH_F

1.3 x 10 -11 exp(-1200/T)

0.31

0.31

CHzFCH2F

1.7 x 10 -I1 exp(-1500/T)

0.59

0.60

CH3CHF2

1.5 x 10 -lz exp(-llOO/T)

1.42

1.46

CH2FCHF2

2.8 x 10 -12 exp(-15OO/T)

2.98

3.17

CH3CF3

2.6 x 10 -13 exp(-1500/T)

22.29

40.2

CHFzCHFz

8.7 x 10 -13 exp(-1500/T)

8.64

10.4

CHzFCF3

1.7 x 10 -lz exp(-1750/T)

10.40

13.1

CHF2CF3

3.8 x 10 -13 exp(-1500/T)

17.06

25.9

CH3CFCIz

2.7 x 10 -13 exp(-1050/T)

5.89

6.68

CH3CFzC1

9.6 x 10 -_3 exp(-1650/T)

12.49

16.6

CHzC1CFzC1

3.6 x 10 -lz exp(-1600/T)

3.28

3.51

CH2C1CF3

5.2 x 10 -13 exp(-1100/T)

3.80

4.11

CHC12CF3

6.4 x 10 -13 exp(-850/T)

1.36

1.40

CHFC1CF3

6.6 x 10 -13 exp(-1250/T)

4.99

5.54

Notes: a. Chemical kinetic data from Hampson, Kurylo and Sander (1989) b. T is absolute temperature in K c. Lifetimes in steady state have been determined in a two-dimensional model assuming a northern hemispheric and constant injection rate, allowing for either 2 % yr stratospheric removal or not d. The l-sigma confidence limits on the lifetimes encompass a range of a factor of two.

145

TROPOSPHERIC LIFETIMES 4. CONCLUSIONS A review of the 14CO method

for determining

ealed a number of areas where changes

the tropospheric

have occurred

hydroxyl

since the original

radical distribution

publication

has rev-

of Volz, Ehhalt and

Derwent (1981). None of these changes has however forced a revision of the approach. They have served to complete our understanding of areas which were difficult to understand in the early work. The chemical kinetic data is notable in this regard. concentrations evaluation.

may have been under-estimated

For the expected ponential

factors

OH

procedure.

halocarbons

It is important

+ halocarbon

and activation

a simple graphical lifetimes,

It is now much easier to understand

chemical

energies,

rate coefficient

it is possible

The '4CO approach

with reasonable

to remember

in the photochemical

precision,

why the early hydroxyl

models as compared

parameters

to estimate

allows the determination 1-sigma confidence

that OH + halocarbon

rate coefficients,

defined

resulting

to the 14CO

in terms

halocarbon

radical

of preex-

lifetimes

of tropospheric

using

halocarbons

limits spanning about a factor of two. hydroxyl

distributions

and halocar-

bon concentrations exhibit important covariance terms so that halocarbon lifetimes are not well-determined quantities. The lifetimes determined in this review are valid only for halocarbons injected at the northern hemisphere

surface

To illustrate

over the latitude range of the major continental

the L4CO method, the graphically +3

determined

land masses and population

lifetimes

centres.

for methane and methyl chloroform

are found to be 7 -2 and 5 ± 2 years, respectively, which are in close accord with our two-dimensional model studies (Cox and Derwent 1981; Derwent and Eggleton 1978), and current literature evaluations (Ehhalt 1988; Prinn 1988). The current methyl chloroform lifetime overlaps the ALE/GAGE 6.3 +-0.9 1.2 years and confirms both estimates since they are completely independent. Lifetimes

of some candidate

studies using the Harwell the subsequent transport parent halocarbon. There

is mounting (Rowland

to become

characterised

1. In considering

fluorocarbons

two-dimensional

model.

and fate of the secondary

evidence

atmosphere

alternative

that man's activities

and Isaksen

in Table 2 based on detailed

These studies should be readily degradation

products

are inducing

changes

extended

liberated

to include

by OH attack on the

in the composition

of the global

1988). Some of the trace gases for which global trends are beginning

play an important

the environmental

have been tabulated

evaluation,

role in global tropospheric

acceptability

of alternative

chemistry,

fluorocarbons,

as described

an attempt

in figure

should be made

to investigate their tropospheric sinks in future scenarios in which the composition of the global troposphere has been grossly perturbed by man's activities. For example, future subsonic aircraft operations may increase local tropospheric that would decrease

OH concentrations

tropospheric

lower bounds on the lifetimes

(Derwent

OH concentrations. of alternative

1982) and other perturbations A scenario

fluorocarbons

approach

can be put forward

could help to put upper and

over the next 50 years.

5. ACKNOWLEDGEMENTS The two-dimensional United Kingdom

modelling

Department

work at Harwell

of the Environment

employed

in this review was sponsored

Air Pollution 146

Research

Programme.

as part of the

N92-15440

TROPOSPHERIC

HYDROXYL

CONCENTRATIONS

HYDROCHLOROFLUOROCARBONS

AND THE LIFETIMES

OF

(HCFCs)

Michael J. Prather NASA/GISS 2880

Broadway,

New

York,

NY 10025

PRECEDING

PAGE

BLp._;K NGT

F;LMED

TROPOSPHERIC HYDROXYL ABSTRACT Three-dimensional

fields of modeled tropospheric OH concentrations

are used to calculate lifetimes against

destruction by OH for many hydrogenated halocarbons, including the CFC alternatives (hydrochlorofluorocarbons or HCFCs). The OH fields are taken from a 3-D chemical transport model (Spivakovsky et al.,

1989) that accurately

of 5.5 yr). The lifetimes

simulates

the global

measurements

of various hydro-halocarbons

of methyl chloroform

are shown to be insensitive

(derived

to possible

spatial vari-

ations and seasonal cycles. It is possible to scale the HCFC lifetimes to that of methyl chloroform by using a ratio of the rate coefficients

for reaction

with OH at an appropriate

temperature,

lifetime

or methane about 277 K.

1. INTRODUCTION Synthetically produced halocarbons that contain chlorine and bromine, often called chlorofluorocarbons (CFCs) and halons, pose a direct threat to the stratospheric ozone layer (e.g., NASA/WMO, 1986; Watson et al.,

1988) and also contribute

substantially

to the greenhouse

1975; Lacis et al., 1981). A single characteristic problems

is their

stratosphere.

long atmospheric

bons, environmentally

acceptable

One key property

loss in the troposphere

fluorocarbons

loss of these HCFCs averaged,

fined as the global atmospheric

sunlight

there will soon be international

Workshop,

in the

restrictions

16-17 May 1989, Boulder residence

on

fluorocarColorado).

time, implying

surface. contain hydrogen by reaction

(hydrochlorofluorocarbons with tropospheric

by the ratio of emissions

annual mean lifetime content

these environmental

only by ultraviolet

must be a short atmospheric

is dominated

(units: kg) will be controlled

The globally

(Ramanathan,

and there is now a search for alternative

(AFEAS

compounds

or at the Earth's

Many of the suggested alternative the atmosphere

concerns,

Protocol,

substitutes

of these alternative

and atmospheric (yr-t).

most are destroyed

As a result of these environmental upon in the Montreal

efficient

of CFCs and hal ons that aggravates

lifetimes;

CFC growth as agreed

forcing of the climate

(kg yr -t) to atmospheric

(yr) of the HCFCs

(kg) divided

or HCFCs),

OH. Their buildup

(against

by the total annual

in

destruction

atmospheric

loss) is de-

loss (kg yr'l).

In this report we derive the lifetime of HCFCs and other hydrogenated halocarbons in two ways. The primary method involves modelling the OH distribution from first principles, specifying or predicting the HCFC

distribution,

tropospheric NOx,

CO,

and then integrating

OH fields are calculated CH4

the HCFC

loss over the globe (e.g.,

from a global 3-D climatology

and other hydrocarbons

(see Spivakovsky

et al.,

Logan et al.,

of sunlight,

temperature,

1989). Uncertainties

OH concentrations occur not only with the kinetic model, but also with the global other trace gases and cloud-cover needed as input to the photochemical model. The OH fields used here were developed Transport CH3CC13

Model

(CTM).

With the CTM,

in order to simulate the latitudinal

sources,

and seasonal patterns,

global transport

x time) is applied here to test various

tropospheric

distribution;

methyl chloroform

climatologies

hypotheses

it is used also to test the accuracy

of the

in a 3-D Chemical

and chemical

losses of

and the global trends (see Spivakovsky

et al., 1989). Similar CTM modelling of all the HCFCs is impractical and geographical location of emissions. Instead, the four-dimensional altitude

03, H20,

in the calculated

and applied to study methyl chloroform we specified

1981). The

and would require OH field (latitude

on the sensitivity

of HCFC

also a history x longitude x

lifetimes

of scaling the HCFC lifetimes

to their

to an assumed

lifetime. 149

PRECEDING

PAGE

BLP_,'K

NGT

F;LMED

TROPOSPHERIC HYDROXYL The second method for deriving HCFC lifetimes selects a reference species with a global budget and atmospheric lifetime (against OH destruction) that is thought to be well understood (see Makide and Rowland, 1981). The lifetime of methyl chloroform,

derived

CH3CC13,

from the ALE/GAGE

analysis

is often used

(Prinn et al., 1987) and is then scaled by the ratio of the rate coefficients for reaction with OH (Hampson, Kurylo and Sander, AFEAS, 1989), k(OH + CH3CC13)/k(OH + HCFC), to calculate the HCFC lifetime. Possible errors

in this approach

are associated

with the assumed

lifetime

for CH3CC13, and with the use

of a single scaling factor that does not reflect the different spatial distribution of the HCFCs. This scaling approximation is tested here for plausible global patterns in the HCFC concentration and for different temperature

dependence

The tropospheric methane

of the rate coefficients.

chemistry

model for OH is described

and methyl chloroform

in Section

in Section

3, and then compare

2. We calculate

the results for methyl chloroform

other published values. The integrated losses for a range of possible distributions in Section 4. HCFC lifetimes and uncertainties are discussed in Section 5.

2. THE CHEMICAL The lifetimes

with

of an HCFC are given

MODEL

calculated

here for the HCFCs,

global distributions of OH from the photochemical (CTM developed

the global losses for

at GISS & Harvard).

as well as for

CH3CCI3,

model developed

CH3Br and CH4, use

CH3CI,

for the 3-D Chemical Transport Model

The model for tropospheric

OH is based on a 1-D photochemical

model (an updated version of Logan et al., 1981 ; DeMore et al., 1987) that has been used to parameterize OH concentrations as a function of sunlight and other background gases (see Spivakovsky et al., 1989). This parameterized chemistry has been used to calculate a three-dimensional set of mean OH concentrations for the CTM grid over one year: the diurnally averaged OH concentrations are stored at 5-day intervals with a spatial resolution of 8 degrees latitude by 10 degrees longitude over 9 vertical layers (see Prather et al., 1987 for CTM documentation) for a total of more than 1/2 million values, even at this coarse resolution. The 5-day average temperatures The local independent Circulation

variables

needed to derive OH concentrations

Model (5-day averages

et al., 1983) and from observed

at each grid point are also stored.

of pressure,

climatologies

ozone column). The observational 4-D fields, and we have assumed the continental

for details

and the maritime

of the assumed

The annual corresponding

averages

trace-gas

see Hansen

(CO, 03, CH4, NOx, H20 above 500 mbar and stratospheric

is that from the available

troposphere

climatology

up to 3 km altitude.

and the chemical

of the zonal mean OH concentrations

annual average

are taken from the parent General

water vapor and cloud cover;

database for most of these species is insufficient to define the necessary zonally uniform distributions with smooth variations over latitude, alti-

tude and season for most species. One exception between

temperature,

temperatures.

Hydroxyl

over the tropics. The OH density peaks at 700-800 reduce solar ultraviolet light below 800 mbar.

ture, density and trace gas abundance.

mbar because

The integrand

et al. (1989)

lb gives the

are highest in the middle troposphere cloud cover

and Rayleigh

over a wide range of conditions

is extremely

150

See Spivakovsky

parameterization.

are shown in Table la; Table

concentrations

The global loss of a gas that reacts with OH is the integral

data we are able to differentiate

non-linear,

scattering

in tempera-

and thus, the average

loss

TROPOSPHERIC HYDROXYL Table l a. Annual Average OH concentration(104cm"_) LATITUDE 90S P(mbar) 100 150 200 300 500 700 800 900 1000

84S

33 31 41 51

76S

32 27 36 44 42

30 24 32 41 40 31

68S

25 21 30 42 44 32 20

60S

52S

25 23 36 43 36 14 11

24 26 45 51 48 21 16

44S

30 33 63 68 65 35 28

36S

28S

20S

12S

4S

4N

12N

20N

28N

36N

44N

52N

60N

68N

76N

84N

90N

38 43 81 89 89 65 52

20 43 52 62 119 139 144 114 92

26 51 57 76 131 154 157 124 105

43 68 65 80 135 159 152 123 103

40 59 58 77 147 180 168 130 112

35 54 52 72 141 182 168 134 112

30 49 48 65 124 171 159 135 112

26 44 43 59 118 159 155 126 107

19 34 36 50 108 139 140 110 88

30 39 80 111 130 116 86

21 28 61 88 108 90 63

17 21 45 64 79 62 43

18 20 40 58 67 53 40

17 21 34 56 77 59 46

20 28 41 53 52 23 17

22 32 46 56 56 26 21

20 33 44 32 32 20 10

Table lb,

Annual

Average

Temperature

(°K)

LATITUDE 90S P(mbar) 1(30 150 200 300 500 700 800 900 1000

84S

206 216 232 247

76S

209 217 236 248 255

209 216 237 248 256 264

68S

211 219 240 254 258 262 267

60S

52S

212 221 244 259 264 268 271

213 224 247 263 268 273 276

44S

214 228 252 267 273 278 282

Quantities

are the annual

No values

for OH or T are reported

At ifigher pressures

36S

28S

20S

12S

4S

4N

12N

20N

28N

36N

44N

52N

60N

68N

76N

84N

90N

217 233 257 272 278 283 287

207 215 222 239 263 277 283 288 291

204 215 225 244 268 282 287 291 295

203 215 225 246 270 283 288 293 297

202 215 225 246 270 283 289 293 297

202 215 226 247 270 283 289 294 297

202 216 226 246 270 284 289 294 298

203 216 225 245 269 283 289 294 297

206 215 223 241 266 280 286 291 293

220 236 260 275 280 285 289

217 231 255 270 275 279 283

215 227 250 265 270 275 277

214 225 248 262 267 270 272

214 223 245 259 264 267 268

214 222 244 258 262 265 268

214 222 242 256 261 263 267

215 217 225 235 239 244 246

zonal average

over Antarctica

of the 4-D fields described

for the extra-tropical the number

Table 2. Global

integrating

Average

dm

96

exp(-1700/T)

dm

105

exp(-1800/T) exp(-2300/T)

dm dm

106 111

dm

to report

a zonal average.

OH concentrations

effective

T (K)

(e.g.,

259 262 263 265

91 65

over mass (dm, from the surface

in temperature

200 mbar).

80

exp(- 1000/T)

Integrals

(above

of points are insufficient

OH (10 4 cm "3)

kernel

dm

(1 + 0.6/P) dz

in the text.

stratosphere

-1700/T

volume

(dz) preferentially

average

OH with the effective

for

cn4),

to 100 mbar)

are weighted

and linear in pressure

weight the lower atmospheric temperature

in the exponential 151

(i.e.,

densities

by different 1 + 0.6/P

factors:

for CO). Integrals

in the upper troposphere.

gives the correct

exponential

global

over

Use of the

integral.

TROPOSPHERIC HYDROXYL is not equal simply to the product a single "global

average

OH concentrations

of averages

(Makide

OH concentration"

averaged

and Rowland,

without qualifying

over the atmosphere

(100-1000

temperature

high temperatures because

dependence

average

OH because

of air in the upper troposphere

to report The global

contribution)

are

The average OH is largest, 11 lxl04 cm -3, with a large exponential factor of-2300/T.

in the tropics (see Table 1). The spatially averaged

of the large volumes

temperatures

result in greater

kernel.

mbar with no stratospheric

reported here in Table 2 for a variety of integrating kernels. when weighted appropriately (by mass) for loss of an HCFC A larger

1981). It is misleading

it as to the averaging

the OH densities

are maximal

at

65x 104 cm

-3,

OH density is smallest,

with low OH concentrations.

given in Table 2 are those needed to get the correct

integral,

and should

not be confused with the optimal scaling temperature in Section 4. (The scaling temperature account for the change in mean OH as the temperature dependence varies.)

must also

3. GLOBAL

integrated

loss frequency for

averaged

LOSS OF CH3CCI_ AND CH4

The globally butions

globally

The effective

losses for methane

(OH and temperature and

CH4

CH3CC13.

and for methyl chloroform

fields described

Tropospheric

are calculated

above) using realistic,

reactions

with OH dominate

by integrating

but fixed tropospheric

the

distri-

the loss of both species,

but

stratospheric losses cannot be ignored and are used in place of OH densities in layer 9 (0-70 mbar) globally and in layer 8 (70-150 mbar) outside the tropics. The stratospheric losses are calculated from a 1-D vertical

diffusion

The assumed

model for stratospheric conditions

ble 3. The lifetime

and resulting

of methane

chemistry

evaluated

atmospheric

at the appropriate

and season.

losses of CH4 and CH3CCI3 are summarized

is 8.7 yr with about 6 % of the loss occurring

Table 3. Global

latitude

budgets

for

CH4

CH4

in the stratosphere

in Ta-

and more

and CH3CCI3

CH3CCIj

Rate coefficient k(X + OH)

2.3xl0-t2e-17°°/T

5.0xl0-12e -lsoo/T

Concentration NH ( 28

°)

SH Atmospheric

content

Atmospheric

losses

total tropics

(2-6 krn)

stratosphere Lifetime

1700/1700

ppb

140/150

ppt

1600 ppb

110 ppt

4580 x 1012g

2930 x 109g

524 x 1012g

534

270 x 10_2g

260 x 109g

29 x 1012g

53 x 109g

8.7 yr

x 109g

5.5 yr

Budgets based on integration of 4-D tropospheric OH fields with zonally fixed, non-seasonal as noted. Stratospheric profiles and losses are included.

152

distributions

TROPOSPHERIC HYDROXYL than half in the tropical

middle troposphere.

loss for methyl chloroform becomes

important

The lifetime

of methyl chloroform

is 5.5 yr. Stratospheric

is about three times more rapid than for methane because photolysis of

in the stratosphere.

Again the tropical

middle troposphere

accounts

CH3CCI

3

for about half of

the global loss.

Methyl chloroform is usually chosen as a reference species for tropospheric mospheric lifetime based on the ALE/GAGE analysis of Prinn et al. (1987). in Table 3 for

CH3CC13

(Spivakovsky

et al, 1989). The ALE/GAGE

industry

with those from the ALE/GAGE

data for atmospheric

global lifetime

emissions,

of 6.3 yr with a reported

analysis

analysis

and the recent 3-D CTM simulations

uses observations

and a 9-box atmospheric 1-sigma range of 5.4-7.5

loss, with a "known" atWe compare the lifetimes

of

model,

CH3CCI

3

to derive

yr. Errors

at 5 surface an annual

in the lifetime

sites,

average

due to uncer-

tainties in the atmospheric emissions used in the ALE/GAGE study have been reduced by recent analyses of CHaCCI3 sources from industry surveys (Midgley, 1989) and from observations (Prather, 1988).

When

the same OH and temperature

(Spivakovsky

et al.,

1989) the integrated

with CH3CC13 concentrations. ing lifetime

fields

are used in the complete

loss correctly

includes

The 3-D CTM simulation

CTM

simulation

all correlations

of CH3CC13

of OH and temperature

showed that the standard OH field (with a result-

of 5.5 yr) and the OH field scaled by a factor of 0.75 (with a lifetime

of 7.1 yr) bracket

the

observations. This range, however, does not include uncertainties in the observations (i.e., absolute calibration) or in the sources. The observed seasonal cycle of CH3CCI3 in the southern hemisphere is not a direct measure

of the absolute

confirmation

OH concentrations;

of the integrated

Such comparisons

emphasize

and they are independent in CH3CC13.

It is difficult

seasonal

however,

variation

the mid-latitude

of absolute calibration

to find other globally

its accurate

of the modeled

photochemistry

simulation

in the CTM provides

OH fields in the southern

which has the largest

seasonal

some

hemisphere. variations,

and sources because they depend on the relative (%) changes

distributed

trace gases with well defined

sources

and trends that can

be used to test global OH concentrations. For example, Derwent and Volz-Thomas (AFEAS, May, 1989; Volz et al., 1981) have used carbon monoxide, both _4CO and _2CO, to test and recalibrate the OH fields in their 2-D model. Another possibility, trends

and sources.

stantaneous

Data for HCFC-22

trend (N/S = 89/77 ppt,

nificant uncertainties

exist currently

HCFC-22

(CHF2C1) has limited data on hemispheric

abundances,

are sparse and barely able to define the hemispheric + 6.5 ppt/yr in 1985, see NASA/WMO,

for the absolute calibration

and atmospheric

ratio and in-

1986). Furthermore, emissions

sig-

of most HCFCs.

HCFC-22 is used as an intermediate chemical in the production of other compounds, and thus its release is only a fraction of production. Recent estimates of HCFC-22 emission (130 Gg/yr in 1985, M. McFarland, personal current

communication) atmospheric

It is not possible from first principles,

are twice as large as previous

budget

at present

to put a formal

or from constraints

the OH fields is chosen

values,

from the limited observations

"one-sigma"

and are now barely able to reconcile

accuracy

using the methyl chloroform

to be 1.3 and is applied

to the lifetimes 153

the

noted above.

on the OH fields used here, budget.

for HCFCs

The uncertainty in Section

5.

either

factor for

TROPOSPHERIC HYDROXYL 4. SENSITIVITYOF HCFCLIFETIME

TO GLOBAL

We use the 4-D fields of OH and temperature relative to another.

Specifically,

DISTRIBUTION

to understand

how to predict the lifetime

how can the lifetime of one species

be scaled to another

of one species with a different

spatial-temporal distribution and loss rate? Idealized tropospheric distributions are used to examine the sensitivity of HCFC lifetime to (a) the temperature dependence of their reaction rates with OH, (b) large interhemispheric cycles

gradients,

(c) enhanced

concentrations

in the boundary

layer near sources,

and (d) seasonal

in concentration. a. Sensitivity

to rate coefficient:

k = A x exp(-B/T)

Two species, X and Y, with the same global distribution and with rate coefficients for reaction with OH that differ only by a constant factor, k(OH + X)/k(OH + Y) = constant, will have lifetimes that scale inversely

by the same factor. In most cases, however,

the rate coefficients

have different

temperature

pendence, B, or pressure dependence (as in the case of CO). We investigate the dependence lifetime on values of B ranging from 0 to 2300 K, by integrating the loss for an atmospheric is uniformly distributed throughout match the CH4 rate, k = 2.3E-12

The integrated

de-

of HCFC tracer that

the troposphere and stratosphere. The A coefficient was selected x exp(-B/T) cm 3 s-l, and stratospheric losses were not included.

global loss rates are given in Table 4a; lifetimes

range

to

from 81 yr (B = 2300 K) to

0.02 yr (B = 0 K). In Figure 1 we show the error associated with predicting the lifetime by scaling to a reference lifetime (9.42 yr at B = 1700 K) using an appropriate temperature in the ratio of reaction rates. This scaling temperature

is not necessarily

also the shift in the reaction-weighted

the mean temperature

mean OH as a function

of reaction

of the OH losses,

but includes

rate (see Section

2 and Table

2). The optimal temperature for scaling the lifetimes is 277 K, and the resulting errors are less than 2 % over the range 800 K < B < 2300 K. Use of a temperature 10 K warmer or colder yields errors in the lifetime of order K) activation

10% when scaling the reference

b. Sensitivity HCFCs

case (B = 1700 K) to greater

(2300 K) or smaller (1000

energies.

to interhemispheric

released

predominantly

lish a global distribution

gradient

from industrialized

countries

similar to that for CFCs (see Prather

in the northern

mid-latitudes

et al., 1987). The north-to-south

will establatitudinal

gradient will have an interhemispheric absolute difference about equal to one year's emissions, and higher concentrations will build up over the presumed continental sources at mid-latitudes. The sensitivity of HCFC

lifetimes

to their interhemispheric

fields (and temperatures sumes a uniformly includes

doubling

gradient

will depend

on hemispheric

in so far as they affect the rate coefficients).

distributed

tracer with OH reaction

the abundance

in either hemisphere

rates appropriate uniformly.

concentrations

of CO in the northern

hemisphere

(reducing

of 03 and NO x. 154

The base case described

in the OH above as-

for CH4, and the perturbed

Results

factor of 2 asymmetry in the HCFC distribution, the lifetime changes OH loss is about 9% greater in the northern hemisphere. Spivakovsky

asymmetries

case

are shown in Table 4b. For a

by only 1.5%. Thus the effective et al. (1989) note that the higher

OH) are more than offset by the higher levels

TROPOSPHERIC HYDROXYL Table4. Lifetime for speciesx against troposphericOH a. Sensitivity

to rate coefficient

A (cm a s-1)

B (K)

2.3E-12 2.3E-12 2.3E-12 2.3E-12 2.3E-12 2.3E-12 2.3E-12

b. Sensitivity

k(OH + X) = A/exp(-B/T)

2300 2000 1700 1500 1100 500 0

to interhemispheric

2:1 1:1 1:2 to boundary

81.2 27.7 9.42 4.58 1.08 .120 .019

lifetime

layer enhancements lifetime

(global) (global, land) ( > 30°N) (>30°N, land) (>30°N) (>30°N, land)

to seasonal

(yr)

9.42 9.33 9.35 9.42 9.41 9.37 9.33

none

d. Sensitivity

(yr)

9.28 9.42 9.57

enhancement

+ 10% + 10 % + 10 % + 10% + 100% + 100%

(yr)

ratio

NH:SH

c. Sensitivity

lifetime

cycle lifetime

amplitude

(vr)

9.42 9.43 9.52 9.97

none _+1% _+10% _+50%

Except where noted X has a uniform mixing ratio throughout the troposphere and stratosphere, but no loss in the stratosphere. Default values are k(OH + X) = 2.3x10 -_2 exp(-1700/T), boundary layer defined as 984-850 mbar, and no seasonal cycle. The assumed seasonal cycle is: positive in winter, (DJF >30°N) & (JJA 30°N) & (DJF _5 x 10 -13 cm 3 molecule -1 s-1 under the temperature and pressure conditions in the troposphere. The lifetimes of the CF2C1 and CFCI2 radicals will then be 5 x 10 -13 cm 3 molecule -1 s-1 at the temperatures and pressures leading to a lifetime of the CF3CHF radical of -Cz haloalkyl radicals are expected to

be closer to the high pressure limit under these conditions and, based upon the data in Table 2, the alkyl and haloalkyl radicals will have bimolecular rate constants for reaction with Oz of > 5 xl0 -13 cm 3 molecule -_ s-l throughout the troposphere. Since the 02 concentration in the troposphere is _> 10 's molecule cm -3, the lifetime of the alkyl and haloalkyl radicals are 5x10"t3

Anastasiet al. (1978)

(298 K) CF30_

2.7x10"29(T/300)'(5±2)

9x10-_2(T/300)'(0.7±1)

0.49

7.6

CF2C102 CFCI202 CCIjO2

4.0x10-29(T/300)'(5±2)

1.0xl0-t_ (1"/300)'(0.7±1)

0.45

8.4

11

IUPAC(1989)

5.5x10-29(T/300)'(5±1)

8.3x]0-12(T/300)-(0.7±1)

0.42

7.1

9.0

IUPAC(1989)

9.2x10-29(T/300)'(6±2)

1.5x10 -tt (T/300)-(0.3±1)

0.32

12

14

IUPAC(1989)

a Calculatedfrom fall-off expressions. b Assumedto be erroneously 10wdue to neglect of absorption of RO2NO

2 products.

194

9.6

IUPAC(1989)

DEGRADATION these reactions are in the fall-off regime between second- and third-order and this is in agreement

with the thermal

decomposition

MECHANISMS

kinetics below atmospheric

data for the peroxynitrates

(IUPAC,

pressure, 1989; see

below). The available limiting low- and high-pressure rate constants ko and koo and the broadening factor F (at 298 K) are given in Table 4, together with the calculated rate constants at 300 K and 760 Torr total pressure constants

and at 220 K and 100 Torr total pressure. for the reactions

of the C1 alkyl peroxy

Under

tropospheric

and haloalkyl

conditions

peroxy

radicals

the bimolecular

rate

with NO2 are within a

factor of _2 of the high pressure rate constant k_o, and the rate constants for the C2 haloalkyl peroxy radicals will be still closer to the high-pressure limit. From the data given in Table 4, the rate constants koo for the reactions

of RO2

radicals

with

koo(RO2+

approximately These

independent

reactions

of temperature

of the alkyl peroxy

form the alkyl and haloalkyl 1980; Reimer

NO2)

and Zabel,

are,

NO2

---1.0 x 10 -l_ cm 3 molecule -1 s-I over the range 200-300

and haloperoxy

peroxynitrates

radicals

(Niki et al.,

I978,

K.

with

NO2

I979;

proceed

Edney

et al.,

solely by addition I979;

Morel

to

et al.,

1986). M RO2+

NO2

_

ROONO2

C. Reaction with HO: Radicals. Absolute rate constants for the reactions of alkyl peroxy and haloalkyl peroxy radicals with the HO2 radical are available only for CH302 and C2H502 , and these data are given in Table 5. The IUPAC

(1989)

recommended

rate constant

expressions

for these reactions

are k(CH302

+ HO2) = 1.7 x 10 -13 e l°°°/T cm 3 molecule "1 s -1 (4.9 x 10 -12 cm 3 molecule -i s-_ at 298 K) and k(C2HsO2 +

HO2)

=

6.5 x 10 -13 e 65°/T cm 3 molecule -1 s-1 (5.8 x 10 -12 cm 3 molecule -_ s-1 at 298 K). The meas-

ured rate constants

for these reactions

are independent

rate constants for all RO2+ HO2 reactions rate constant of k(RO2+

HO2)

_

of pressure

(IUPAC,

1989). Assuming

are similar to those for these two reactions,

that the

a room temperature

5 X 10 -_2 cm 3 molecule -1 s-1 at 298 K

and k(ROE+

HO2) _ 3.4 xl0 -13 e s°°/T cm 3 molecule "1 s-1

has been recommended by Atkinson (1989a) for all alkyl peroxy radicals. Clearly, a much wider data base is necessary to test this assumption since, for example, Niki et al. (1980) have obtained evidence from a product

study of the C1 atom reactions

with CHaCI and CH2C12 that the room temperature

constant for the reaction of the HO2 radical with CH2CIO2 is significantly HO2 radical reaction rate constant for the CHC1202 radical. These reactions

have been assumed

to proceed ROE+

by the pathway.

HO2 _ ROOH 195

+ O2

rate

slower than the corresponding

DEGRADATION MECHANISMS Table5. Absolute

rate constants for the reactions of alkyl peroxy (RO_) radicals with the H02

radical

10 lz x k ROz"

(cm 3 molecule"

CH302

CzHsO2

(K)

Reference

8.5 --+ 1.2 6.5 + 1.0 3.5 _+ 0.5

274 298 338

Cox and Tyndall

3.5 a

298

McAdam Kurylo

et al. (1987)

6.8

_+ 0.5

228

Dagaut

et al. (1988a)

5.5

_+ 0.3

248

4.1

+ 0.3

273

2.4 2.1

+ 0.5 _+ 0.3

340 380

5.4

+ 1.1

300

6.8

_ 0.9

303

6.3

_ 0.9

7.3 6.0

Jenkin

et al. (1988)

295

Cattell

et al. (1986)

_+ 1.0 + 0.5

248 273

Dagaut

et al. (1988b)

5.3

+ 1.0

298

3.4

+ 1.0

340

3.1

+ 0.5

380

Jenkin et al. (1988) observed

et al. (1987),

the additional CD202

contributing

et al. (1987)

298

However,

with this channel

(1980)

_+ 0.4

value as cited by Kurylo

and postulated

s")

2.9

a Revised

HO2 radical,

at T

"-40%

+

Dagaut

the formation reaction HO2

--"

et al. (1988a)

and Jenkin

of HDO from the reaction

et al. (1988).

of

CD20

_

with the

pathway, DCDO

of the overall

+ HDO

reaction

+ 02

at room temperature.

D. Reaction with Alkyl and Haloalkyl Peroxy (RO2) and Acyl Peroxy (RCO_) Radicals. The available absolute rate constant data for the self-reactions of alkyl and haloalkyl peroxy (RO2) radicals and for their reactions with other alkyl peroxy and acyl peroxy radicals are given in Table 6. Clearly, the majority of the data concern the self-reactions of the alkyl peroxy radicals, with the only data for cross-combination reactions

being for the reactions

Since the tropospheric will be low (because

of the CH30_ radical with tert-butyl

peroxy

and acetyl peroxy

radicals.

formation rates of the haloalkyl peroxy radicals being dealt with in this assessment of the low rate constants for the reactions of the OH radical with the HCFCs and 196

DEGRADATION

HFCs

in question),

is expected

self-reactions

that the dominant

with will

be the CH30_

reaction

of the

RO_

CH30_

radical

an uncertainty

Table

6.

Rate

of _ _+ a factor constants,

haloalkyl

k

peroxy

=

with which

data

RO2

radicals

C2H502

Ae -B/T, for the radicals

C2H502

CH3CH2CH202 (CH3)2CHO2 (CH3)3CO2

+ (CH3)2CHO_

gas-phase

with

RO;

CH30

and

combination RC03

+

These

CH2CICH202

reactions

of RO2

+

RIR2CHO2

reactions al.,

of CH302,

1981,

room

(b) not being 1982;

C2H_O2,

Anastasi

temperature

rate

< 0.1.

For the reaction

Parkes

(1981)

at around significance RO2

also

room

radical

accessible

constant

1983;

11_v +-IO0 3oo

0.86

IUPAC

(1989)

3

IUPAC

(1989)

0.01

IUPAC

(1989)

0.00019

Kirsch

et al. (1978)

+ 0.5

Parkes

(1975)

35.7

+ 5.7

Dagaut

et al. (1988c)

2200

+ 300 4775

+

170

ratios

proposed

temperature.

that

IUPAC (1989)

-1020

3.1

-735

+ 95

37.8

+ 4.5

Dagaut

et al. (1988d)

3.3

-700

+ 100

30.7

+ 6.5

Dagaut

et al. (1988d)

IUPAC

(1989)

for the self-reaction

can proceed _

R3R4CHO2 for tertiary

ka/k

_

RO2 1989).

radicals.

reaction

radical,

reactions. 197

channels

+ +

radicals

(c)

02

and Parkes,

and secondary

k = ka + kb + radical, were

concluded

that reaction

1981;

(1975)

product

data

Niki

_0.5,

with

and Kirsch

(a) and (b) above, pathway

for the self-

RO2 radicals,

k c) are both

Parkes

pathways

and further

(b)

02

data are available

(Kirsch

For the primary

(a)

+ 02

RaR4CO

Product

with the CH302

Niki et al. (1980)

of the CHC120_

+

RIR2CHOOCHR3R4

and kb/k (where radical

reaction

+ R3R4CHO"

RIR2CHOH

and (CH3)3CO_

IUPAC,

by the

RIR2CHO" _

the operative

However,

Reference

1.1

radicals

of the (CH3)3CO2

and

1.2

(CH3)2CHO2

et al.,

alkyl

3.6

R3R4CHO2 +

of

-220 ± 220

+ R3R4CHO2

RIR2CHO2

channel

reactions

110

R2R2CHO2

with

K

1.7

CH3CO3

combination

for the

radicals

1.0

+ CHEFO_

_

will react

constant

l0 is x k (298 K) (cm 3 molecule "1s "1)

1700

+ CHEC10_

CH2FO2

It

B (K)

16

+ (CH3)3CO_

+

radicals

a rate

-_ s -_ at 298

+ CH3CH2CH202

CH2C1CH202

peroxy

6) suggest

importance.

of

CH_O_ + (CH_)_CO_ CH2C10_

haloalkyl

(Table

) _ 2 x 10 -_3 cm 3 molecule

CH302

+

will be of minimal

these

available

1013 x A (cm 3 molecule -1 s"a) +

radicals

of 5.

(ROE)

Reaction CH302

other

CH302

peroxy

radical

and the limited with

+

haloalkyl

or RCO_

radical,

k(RO2

with

of these

MECHANISMS

with

et the kc and

ka = kb

(b) was of minor

are required

for these

DEGRADATION

MECHANISMS

For the self-reaction of the tert-butyl peroxy radical, Kirsch and Parkes (1981) = 0.12 at 298 K, with this ratio decreasing rapidly with increasing temperature. 4.3.

Reactions

of Alkoxy

and Haloalkoxy

unimolecular

that kc/k

(RO') Radicals

For the CI and C2 haloalkoxy radicals involved in the tropospheric degradation and HFCs considered in this article, the reactions of concern are with 02, RIR2CHO"

determined

+ 02

-*

RIR2CO

+

reactions

of the HCFCs

HO2

decomposition, R1RECHO

and reaction

--' RI

+ R2CHO

with NO and NO2. RIR2CHONO RIR2CHO"

+ NO _

R_R2CO

+ HNO

RtR2CHONO2 RIR2CHO"

+

NO2

_ A. Reaction

with 02. Absolute

only for the CH30",

rate constants

C2H50" and (CH3)2CHO"

Table 7. For the methoxy Wantuck

RIR2CO

< 300 K (the Arrhenius

plot exhibits

k(CH30" This recommended (1987) and IUPAC

for the reactions radicals,

radical the rate constants

et al. (1987) are in good agreement,

of Gutman

curvature

of alkoxy radicals

and the rate constant

and Atkinson

marked

+ 02)

+ HONO

et al. (1982),

(1989a)

s-t and 7.2 x 10-14 e -1°8°/T cm 3 molecule -1 s-I, respectively.

(Atkinson,

1989a). Similarly,

with a preexponential

et al. (1985)

and

that for temperatures

> 500 K).

is that of Lorenz et al. (1985), and is similar to the NASA of k(Cn30" -t- 02) = 3.9 x 10 -14 e -9°°/T cm 3 molecule -1 Combining

al. (1982) at 296 and 353 K for the C2H50" radical with a preexponential s-' leads to + 02)

are given in

= 5.5 x 10 -14 e -l°°°/T cm 3 molecule -I s-_

temperature expression (1989) recommendations

k(RCH20'

Lorenz

recommended

at temperatures

with 02 are available

data obtained

the rate constants

of Gutman

et

factor of 3.7 x 10 -14 cm 3molecule -1

= 3.7 x 10-14 e -46°/T cm 3 molecule -_ s-I

the data of Balla et al. (1985) for the (CH3)2CHO"

radical can be combined

factor of 1.8 x 10 -14 cm 3 molecule -1 s-1 to yield (Atkinson, 198

1989a)

DEGRADATION MECHANISMS Table7. Absoluterate constants,

RO"

k, for the gas-phase reactions of alkoxy (RO) radicals with 02

1015 x k

T

(cm 3 molecule "t s"1)

(K)

Reference

7 x 105

Room

Reference

Carr et al. (1986)

temperature "-'1 x 1014

CFC120' --*COFCI + CI

CC130' -_ COC12 + CI

5335c

_1 x 1014

CHCI20' -# HC(O)CI + CI

_1 x 1014

5940c

253

Rayez et al. (1987)

>3 x 104

253

Lesclaux et al. (1987)

8 x 104b

233

Rayez et al. (1987)

>1 x 105

233

Lesclaux et al. (1987)

2 x 105b

298

Rayez et al. (1987)

> 105

298

Niki et al. (1980)

_1 x 1014

10320c

0.1b

298

Rayez et al. (1987)

CHFCIO' -' HC(O)F + CI

"ol x 10TM

5230c

2 x 106b

298

Rayez et al. (1987)

CHF20' -' COF2 + H

_1 x 1014

17770c

1 x 10"12b

298

Rayez et al. (1987)

CHFCIO' --' COFCI + H

_'1 x 1014

14800':

3 x 10sb

298

Rayez et al. (1987)

"_1 xl014

14900c

2 x 10-Sb

298

Rayez et al. (1987)

_1 x 1014

13340c

4

298

Rayez et al. (1987)

",'1 x 1014

14540c

6 x 10"Sb

298

Rayez et al. (1987)

CH2CIO"

HCHO + C1

4880c

7 x 104b

_

CH2CIO'

HC(O)C1 + H

_

CHCI20" -_ CH2FO'

_

COC12

+

H

HC(O)F + H

X 10 6b

a High-pressure limits. b Calculated from cited Arrhenius expression. c Calculated.

Gillespie

et al. (1977),

(c) For the CHCI20'

Suong and Carr (1982) radical,

decomposition

and Withnall

and Sodeau

by C1 atom elimination

(1986).

dominates

over reaction

with 02

at room temperature and atmospheric pressure. However, this may not be the case at the lower temperatures and 02 concentrations encountered in the middle and upper troposphere. In contrast, decomposition of the CH2C10" radical is slow and the reaction with 02 CH2CIO"

+ 02

-_ HC(O)CI 200

+ HO2

DEGRADATION MECHANISMS dominates

at room temperature

and is expected

For the C2 haloalkoxy (a) For

that decomposition

(b) For

higher

Thus, for example,

pressure

Sanhueza

(X = F, CI and/or

by Sanhueza

haloalkoxy

radicals

CF2C1CCI20" CCI3CF20"

CF2C1CF20"

conditions,

the important

that:

(presumably) energy

pathways

that reaction

are sufficiently

en-

with 02 will dominate.

H), the C-F bond dissociation

that C-C bond cleavage

energy is

occurs.

and Heicklen (1975) and Sanhueza et al. (1976), the dominant

CFC12CFC10"

For tropospheric

concluded

H), the decomposition

(X = F, C1 and/or

as discussed

et al., 1976; Niki et al., 1980),

conditions.

et al. (1976)

than the C-C bond dissociation

for the following

of air (Sanhueza

for all tropospheric

does not occur, and hence it is expected

radicals

CX3CF20"

sufficiently

reactions

radicals,

radicals

CX3CH20"

dothermic

and atmospheric

to totally dominate

are _ _

CFC12C(O)F

+ C1

CF2CIC(O)C1

+ C1

"-* COF2

+

(_C13

-_

+

CF2C1

COF2

parameters

are the rate constant

ratios for the reactions

of

the alkoxy and haloalkoxy radicals with 02 and their various decomposition pathways. It is anticipated that the rate constants for these processes will depend on their heats of reaction [since (Table 8) the preexponential factors for the various decomposition pathways appear to be reasonably similar at "_1 x 1014 s-X]. Since in most cases the heats of formation of the reactant alkoxy and haloalkoxy radicals are not known

with any certainty,

the reaction

products

it is possible

for the reactions

that the differences

between

the summed

of the various alkoxy and haloalkoxy

radicals

heats of formation

of

can be used as a tool

in deciding the relative importance of these reaction pathways. Table 9 gives examples of the summed heats of formation of the products for the various reactions of the ethoxy, 2-butoxy, CH2CIO" and CH2C10" radicals. These data in Table 9 show that the H atom elimination pathway is the most endothermic decomposition route (being relatively tent with Table

close to the C1 atom elimination

The differences in the heats of reaction,/[AHO2 reaction to the nearest kcal mol -t) are then: C2H50", 45; 2-butoxy, temperature reaction

pathway

for the CH2CIO" radical,

consis-

8).

and atmospheric

pressure

with 02 (Carter and Atldnson,

AHdecomposition]!

42; CH2CIO

of air, the removal 1985); 2-butoxy,

processes

reaction

= A(AH), in kcal mol -_ (rounded , 48; and CHCI20", 30. At room

of these RO" radicals

with 02 and decomposition

are: C2H50", by C-C bond

cleavage in an approximately 60%/40% split (Carter and Atkinson, 1985; Atkinson, 1989a); CH2C10", reaction with 02 (Niki et al., 1980); and CHC120", CI atom elimination (Niki et al., 1980). Thus, as expected, there is a relation between the reaction pathway and the difference in the heats of reaction between the pathways. For A(AH) >43 kcal mol -t, reaction with 02 dominates, while for A(AH) 1 x 105 (233K)

Lesclaux et al. 1987

> 3 x 104 (253 K)

Lesclaux

et

al. 1987 CCIF20

--_ CF20

+ CI

> 7x

105 (298K)

Carr et al. 1986

Reactions

of hydrochlorofluoroethoxy

radicals

Important information concerning the ways chloro- and chlorofluoro-ethoxy radicals react or decompose, can be obtained from studies of the chlorine atom-initiated oxidation of chloro- and chlorofluoroethylenes which proceeds by a long chain, free radical process. These reactions have been extensively studied, mainly by the groups of Shumacher, Huybrechts and Heicklen (see Muller and Schumacher, 1937a,b; Schumacher

and Thurauf,

1941; Huybrechts

and Meyers,

1966; Huybrechts

et al. 1965; Sanhueza

Meicklen, 1975b,c,e) and the results have been collected by Sanhueza et al. in a review these data, some general rules can be drawn on the reactions of such radicals. i - Chlorine

atom detachment CX3CYCIO

(XandY

--*

CX3CYO

= H, ClorF) 224

+ C1

(1976).

and From

DEGRADATION MECHANISMS This type of reaction

always

occurs preferentially

if Y = C1 or F, independently

of the nature of the

CX3 group. For example, CCI3CC120, CHC12CCI20, CC1FzCC120, CCI2FCCIFO, CCIF2CC1FO cals essentially undergo this type of reaction. By studying the photooxidation of methyl chloroform, son et al. (1984),

showed

that the radical CH3CCI20

also dissociates

radiNel-

in this way.

ii - C-C bond cleavage CX3CX20 This reaction

always

occurs

for radicals

--' CX3 + CX20

of the type

independently

CX3CF20,

of the nature of

CX

3.

The situation is not as clear for CX3CHFO or CX3CHC10 radicals, since they can either undergo a C-C bond cleavage or react with oxygen. It seems however that the C-C bond cleavage is the most favourable process

for these radicals.

mosphere

of air,

CH2CICHC10

In a study of CI atom sensitized

Spence

and Hanst

and CH3CHCIO

essentially

Small amounts of acid chlorides oxygen.

The same conclusion

ethylenes

(Sanhueza

Apparently,

(1978)

have, however,

was reached

preferentially

gen seems to be a minor process

--_ CX3CXO

for CX3CHXO

radicals.

relevant

to this review.

reaction

for C2H50,

iv - Oxidation

of the

resulting

radicals

from the reaction oxidation

with

of chlorinated

react in the same way.

has not been observed.

product

HO2

However,

of the type CX3CH20,

it will be considered

The rate constant

taking into account

yielding

for this reaction

as a possible

is assumed

the effect of the halogen

radical is one of the major uncertainties

This radical

in laboratory

the elimination

+

to be

atom on the

radical

CF30

of the CF30

of perfluorocompounds.

be important

as a result of the C-C bond cleavage.

been detected,

occurs in the cases of radicals

in the compounds

knowledge,

in one at-

CHC12CHCIO,

This has been shown for CC13CH20 (Nelson et al. 1984; Sperce (Sperce and Henst, 1978). As shown above, the reaction with oxy-

one tenth of the equivalent H atom reactivity.

containing

ethanes,

CC13CHC10,

with oxygen

this reaction

The oxidation

chloride

that CX3CHFO

from CX3CCIHO

a halogenated acetaldehyde molecule. and Henst, 1978) and for CH2CICH20 channel

of chlorinated

in the study of the C1 atom sensitized

et al. 1976). It can be expected

CXaCXHO

Obviously,

oxidation

that the radicals

yield formyl

CX3CC10

the CI atom detachment

iii - Reaction

showed

is formed

systems

in the degradation

appears

to be CF202.

of an F atom either thermally

in the atmosphere

in the mechanism

of CF3 via According

or by reaction

CF202

to current

+ M

CF30

+ 02 -'* CF20

-_

CF20

+

F + M

AH ° =

+ 36 kJ mo1-1

+

FO2

AH ° =

+ 42kJmo1-1

225

and the major

C-

thermochemical

with 02 is too endothermic

:

CF30

of degradation

to

DEGRADATION MECHANISMS Accordingly

it has been hypothesized

that heteregeneous

of CF20 in laboratory systems. It is important ways may occur in the atmosphere. 6 - Photochemical Halogenated

therefore

reactions to establish

whether

for the formation

other homogeneous

path-

reactions

hydroperoxides

Information on the photolysis of halogenated hydroperoxides, photolysis is likely to be rather

hydroperoxides is sparse. By analogy with the alkyl slow and to occur via dissociation of the central O-O

bond leading to the same alkoxy radical as that produced by reaction NO. For modeling purposes, it is recommended to use J(CH3OOH) CX_OOH Carbon',/I

are responsible

+ hv --' CX30

of the original peroxy for the reaction :

radical

with

CFCIO

and

unaffected

by

+ OH

Halides

The absorption

spectra

of the carbonyl

halides,

CX20,

have been determined

for CF:O,

CC120 (Baulch et al. 1980). The molecules absorb only in the deep UV and are virtually sunlight in the troposphere. Photolysis leads to elimination of a halogen atom : CX20

+ hv ---, CXO

+ X

The fragment radical CICO is unstable with respect to decomposition to CI + CO and the same is probably true for FCO, although the thermodynamic stability of this radical is still uncertain. The photochemistry

of CHXO (X = F or C1) has been investigated

in the case of CHFO (Okabe,

1978).

It appears that substitution of halogen on the carbonyl carbon atom, X-C = O, has the effect of shifting the n_Fl* electronic absorption in the C = O group to higher energies (blue shift in wavelength), thus reducing

the rate of photoabsorption

ation rates are therefore

in the lower part of the atmosphere

likely to be reduced in consequence,

Although CX3CHO, CX3COCX3,

Photodissoci-

although the effect may be modified by changes

in the quantum yields, which are not known. These arguments carbonyls of the type CX3CXO. Halogenated

quite dramatically.

are also expected to apply to fully halogenated

aldehydes there there

is little information is considerable

which

photolyse

on the photochemistry

information

of the halogenated

on the photochemistry

in the near UV following

n-q-I*

aldehydes

of the halogenated

excitation

(Macket

of the type ketones

and Phillips,

e.g. 1962).

Since the absorption by aldehydes in the corresponding near UV band is also an n---,I-l*,absorption of fully halogenated ketones, (CF3)2CO, (CF2C1)2CO and (CC13)2CO, is shifted up to 20 nm to the red, making these molecules photodissociation

more strongly

absorbing

in the solar UV troposphere.

near 300 nm are 0.8 (Whytock

and Kutsche,

Moreover,

the quantum

1988), i.e. substantially

simple aliphatic ketones. Comparing this analogy for aldehydes of the type CX3CHO, rather rapid photolysis of these compounds according to the reaction : CX3CHO

+

hv---, CX3 + HCO 226

higher

yields for than for

we may expect

DEGRADATION MECHANISMS However,

at short wavelength,

another

photodissociation

CX3CHO A reasonable

approximation

H + HCO channels A novel process C-C bond

rupture

+ hv --* CHX3

this process

ketones

+ hv _

may be open for the (slower)

of OH with halogenated

For the hydroperoxides,

photolysis

of a C1 atom rather

than

CX3CHO

+ OH

CX3OOH

+ OH _

:

+ C1

the -CH0 group)

--* n20

+

H20

through

OH at-

CX3CO

to the C atom (relative

For the rate coefficients

can degrade

+ CX3OO

due to the deactivating

of 2 to compensate

type carbonyls

and aldehydes

the H-atom attached

by a factor

+ C1

of CX3CXO

hv ---' CX2CXO

+

peroxides

than the Hoo atom,

C_ and C2 fragments. H202 reduced

is the elimination

CF2CICOCF2

Halogenated hydroperoxides and aldehydes (containing tack. The reactions can be written as follows :

to be abstracted

via the

e.g.

CX2CICXO

7 - Reaction

+ CO

in the atmosphere.

in the chloro-substituted

CF2CICOCF2C1 This channel

may occur :

would be to use the same J value as for HCHO photodissociation

for modelling

observed

pathway

to the peroxy

effect of the nearby

the preferred

estimates

for the lower number

link) are less likely

halogen

atoms in both

are those for reaction of abstractable

of OH

H-atoms.

+

The only

halogen substituted aldehyde for which the rate coefficient for OH attack appears to have been measured is chloral, CCI3CHO, derived from the photo-oxidation of methyl chloroform (Nelson et al. 1984) for which a value of 6.2 x 10 -12 cm3molecule-ts -_ was obtained at 298 K. In the same study, the rate coefficient for OH attack

on acetyl chloride OH

was determined of H abstraction. fluorocarbonyl

:

+ CH3CCIO

--_ H20

+ CH2CCIO

to be 7.2 x 10 -_4 cm 3 molecule -_ s-t showing Fluorine

substitution

is also expected

that the C-CIO group also reduces

to show a similar deactivating

the rate

effect in analogous

compounds.

The rate of the HCFO

and HCC10

molecules

with OH is unknown

OH + HCXO A value of approximately vation by the halogen

1 x 10-t2 cm3molecule

-, H20

+ CXO

- _s-_ is estimated,

atom for H-abstraction. 227

:

taking into account

the effect of deacti-

DEGRADATION

8 - Rainout_

MECHANISMS

washout

All oxygenated

and dry deposition

processes

secondary products from the oxidation of HCFC's

aldehydes, carbonyl halides and acid halides (e.g. CX3CFO), in the precipitation

elements

and Henry's

law constants

precipitation

elements

and also by dry deposition for these gases is required

for the carbonyl

and CFC's,

hydroperoxides,

halogenated

will be subject to removal by solution/hydrolysis

at the earth surface.

Knowledge

in order to assess the importance

halides CCI_O, CFC10 and CF20.

of the solubility of removal

Since these molecules

in the

are very

stable towards gas phase removal, removal by wet and dry deposition probably has an important role in determining their atmospheric lifetime. Recent estimates of the lifetime of phosgene, based on measured concentrations

and the estimated

source

strength

(Wilson

228

et al. 1989), are about 2 months.

DEGRADATION

APPENDIX

III (R.A.

COX

Recommended

AND

R. LESCLAUX)

rates

coefficients

for modelling

atmospheric

MECHANISMS

degradation

of hydrochlorofluorocarbons A schematic in Figure reactions marised

diagram

1. In order

illustrating to formulate

and 4 photochemical in Table

the degradation

A and

the basic

reactions

pathways

chemistry,

are required.

for the photochemical

OH

+

of a typical

knowledge

hydrochlorofluocarbon

of the rate

The best estimates

parameters

HCFC

in Table

coefficients

B.

,/ K-1

[

CX3CHXO0

_

+NO_

I

6:1

_j+h

J

CX3CHXO

Peroxynitrate

/

I Hydr°per°xide rv

K5

:X CI 1_

Minor

products

Figure 1. Tropospheric

shown

Degradation

in "broken"

Pathways

boxes,

for typical

229

(X=H} +0__)

major

products

CFC substrates.

for 10 thermal

of the rate coefficients

+ 0 I'D1

HCFC

is shown

in "full"

boxes

are sum-

DEGRADATION MECHANISMS _v ON+

()3_X2)

u_

b tr,

LL

:OH

+ ()3

_ X3

to-,

¢5 --

"O tOO _7 ¸

L'

0_ ()H3

LL

_ _3

_r'

_

3

o.

_

T

+ HO

E_

J

_9 "1"

+ _,7

6'

O :OH+OX3

_4

_Xo_rO+O_[

©

o

+

+

+

q

© , ;i_¸

q

,-e

C co ¢-

T

©

5..

u_

c

g_

b

E

+

>

d

O

E

:OH

+ ()HD

_XD_rO+OH

r" 0

¢,

1,3 + OXDt

X3

_ OH

o ,-r.

tO

_v

OrXD+

_XD*--

.C = O + HzO + 02 via formation entirely

ruled out. The products, 11987; CODATA,

Reactions

Involving

The atmospheric

of an adduct

the possibility [ROOOOH]

haloalkryl hydroperoxides,

to react further with HO radicals to regenerate Report,

However,

evidence

of an alternative

complex

are intermediate

formation

products

for the

mechanism has not been

which

are likely

ROO radicals, in analogy to the reaction of CH3OOH

(NASA

1982, 1984).

RO Radicals reactions

of the haloalkoxy

been carried out at room temperature

RO radicals are less well established.

and atmospheric

Simonaitis

studies have

pressure of air for the following RO radicals; CH2CIO

+ 02 --' CHCIO + HO2 (Simonaities and Heicklen, --* CHCIO + CI (Simonaitis and Heicklen, 1979; CF3-xCIx-_O + C1 (1 _ 6.0 (Hybrechts

and Meyers,

1966; Bertrand et al., 1968); CH2C1CC120

_ (CH2CICCIO

+ C1)/(CH2C1

+ CC120)

is extremely

25 kcal/mol),

fast under all tropospheric reaction

(2')

R'CH2 for less than 0.1% (R'

b. ROJRO

(i) RO2/NOx

high R-O2 bond

and RO2 is the only form in which

interactions

+ 02 _

Due to the relatively

between

R exists in

R and 02 leading to an unsaturated

R'-H = CH2 + HO2

= CH3) of the overall

reaction and can safely be discarded

for the simpler

conversion

Unlike step (a), the conversion on the ambient conditions.

mechanism

of alkylperoxi

radicals to alkoxi radicals

- step (b) - depends

interactions:

In the continental boundary oxides are normally present with NO, viz. (3)

Alternative

RO2 (+M)

conditions.

(2) is not reversible

perceivable levels in the troposphere. HC and HO2, viz.

account HC's.

_

radicals, viz.

layer as well as in the upper troposphere/lower stratosphere, sufficient nitrogen for the alkylperoxi radical chemistry to be dominated by the fast reaction

RO2 + NO _

254

RO

+ NO2

DEGRADATION MECHANISMS The rate constants

for this process

n-C3H7 and i-C3H7 (Atkinson

at 298 K are of the order

et al.,

1989). However,

tween RO2 and NO may also proceed (3') The importance and 4.4% Under

of this process

general application initrates,

where

increases

with chain length and amounts

to
©

0.4

®_=

0.3

CH3CCl3

HCFC-123 HCFC-124

0.2

HCFC-141b

0.1

!

0 0

10

1 20

30

40

50

Year

Figure 25. Calculated Time-Dependent Emission of Halocarbons. (LLNL l-D).

Relative

372

Chlorine

Loading

Following

a Step

Change

in

STRATOSPHERIC OZONE

CFC-12

CFC-115

0

50

100

150

200

250

Time

300

350

400

450

500

(Yr)

Figure 26. Calculated Time-Dependent Relative Emission of Halocarbons. (DuPont l-D).

373

Chlorine

Loading

Following

a Step

Change

in

STRATOSPHERIC OZONE 8. ACKNOWLEDGMENTS The authors are grateful vironmental

Acceptability

for the support

received

Study (AFEAS).

for this work from the Alternative

Additional

funding was provided

Allied-Signal Corporation, Atochem, E.I. du Pont de Nemours Chemicals and Polymers Limited, and Montefluos SPA. Work at AER, Inc. is also supported Atmospheric Theory and Data Program Aeronautics and Space Administration, Energy (W-7405-ENG-48).

by the National

En-

by the following companies:

& Co., Hoechst

Aeronautics

Fluorocarbon

Aktiengesellschaft,

and Space Administration,

ICI

Upper

(NASW-4080). Work at LLNL is also supported bv the National as well as being under the auspices of the U.S. Department of

374

STRATOSPHERIC OZONE APPENDIXA: RELATIONSHIP BETWEENFORMSOF ODP It is helpful to look at the various

formulations

tween them. We have chosen our definition release

of a given compound

for ODP and explore

rate of CFC-I 1 at steady state. Subsequently,

ozone change resulting

we showed,

at time t = to a stimulus containing

S(to) [which in this example

gas into the atmosphere]

Properties

In terms of physical specific.

STEADY

STATE

strength

to the ozone column

to a release

change]

of a set mass of chlorine

make the assumption

that the response

to Dive:

g(t) are that:

g(o_ ) = 0 (i.e.,

is species

to the source

that the ratio of cu-

= G(t-to)/S(to)

of the function

within the reacting

corresponds

a constant

equivalent to ODP. The purpose of in order to define the relationship(s)

corresponds

at time to. We furthermore

is linear so that it can be normalized g(t-to)

[which in this example

be-

from the same mass release

based on model exercises,

mulative effects following a one-time input of gases was virtually this section is to examine the background mathematical formulations between the tbrmulations. function

relationships

for ODP to be the column ozone change following

divided by the column

Let G (t-to) be the response

the background

processes,

the response the function

system (atmosphere)

Let us first examine

decays

to 0 at infinite

g(t-to) contains

time),

the results from the transport

and is specific to one set of reaction

the case of a steady-state

response.

If a stimulus

parameters,

and chemistry and therefore

started at time = 0 and held cons-

tant at S = S o until steady state is realized, then the steady-state response is reached the integrated response from all gas released over history and is of the form:

at time T and is

to =T Gss = f So*g(T-to)

dto

to =0 Since by definition

of steady state, it is insensitive

at time, t = - . Thus, Gss can be expressed,

to starting

without

time, so we could have started

loss of generality,

the release

as:

to=T Gss

= f S O * g(T-to)dt o tO

Therefore

if we use the notation

the corresponding

response

=

-_

that Gss-x is the steady

for CFC-I 1, then ODP(ss) 375

state response can be expressed

for compound as:

x, and Gss-11

is

STRATOSPHERIC OZONE ODP(ss)

Gss-x/So-x

=

Gss-11/So-11 or,

T f gx(T-to)dt o -OO

ODP(ss)

=

(A)

T f gll

(T-to)dt o

-00

With a substitution

of integration

variables

of :T-to.

equation

A becomes:

O -f gx(t)dt +oo ODP(ss)

= 0 -f g 11 (t)dt

or,

oo

-f gx(t)dt ODP(ss)

=

0

(B) oO

-f g 11 (t)dt 0

PULSED INPUT Now, let us focus on the ratio of integrated responses to a pulsed input. For a pulsed input of value PS at time to, the integrated resulting effect, GP, on the system over the ensuing period is: oO

GP

= f PS *g(t-to)

dt

to Since PS is constant,

GP becomes:

GP

= PS*

f g(t-t o) dt to

376

STRATOSPHERIC OZONE We can again change the integration variable such that T = t-to and since the values for PS will be the same both in the numerator and the denominator, the ratios of integrated responses reduces to: oo

GP-x

f gx(T) dT 0

(c) oO

GP-11

Which

is the same functional

f g 11 (T) dT 0

form as ODP expressed

by equation

B.

Therefore we have shown mathematical equivalence as long as we have linear relationships between release (stimuli) and ozone chance (response). Real world interpretations as well as model exercises indicate that the relationships

are not exactly linear. Therefore,

discrepancies

to pulsed releases do exist but are caused by the (minor) non-linearities cal round-off errors associated with the numerical models.

377

between ODP and ratio of responses of the phenomena

and/or

numeri-

IX.

Relative

HALOCARBON GLOBAL POTENTIALS

Effects

on Global

Warming

WARMING

of Halogenated Methanes Industrial Interest

and Ethanes

of Social

and

D. A. Fisher and Charles H. Hales E. I. du Pont de Nemours & Company Wilmington, DE Wie-Chyung Wang, Atmospheric

Malcolm K. W. Ko and and Environmental Research, Cambridge, MA

_"

/

/

N. Dak Inc.

EDING

PAGE

Sze

BLAr,_K NOT

FILMED

GLOBAL WARMING EXECUTIVE Halocarbon of the relative

Global Warming environmental

Potentials

SUMMARY

have been defined

effects of halocarbons

the HGWPs of the hydrohalocarbons to a lesser degree on the molecular

and calculated

to be made.

in order to allow estimates

The results presented

depend primarily on the atmospheric IR absorption characteristics.

lifetime

here indicate

that

of the compounds

and

The reduction in HGWP that might be expected due to use replacement of a CFC by a hydrohalocarbon can be estimated by taking the ratio of the HGWP of the hydrohalocarbon to the HGWP of the CFC it would replace.

For example,

± .010)/(3.05)

= 0.085

use application

the reduction ± 0.003.

Of course,

deled chemistry

and dynamics

radical

reactions

to assumed

influenced

by the changes

depending

times,

once better data is available

to be reasonably

values of other radiative

Calculated time-dependent longer

quantities

and their direct effect on the chemical

with the respective

values appear

insensitive

or increase

the relative

uses of CFC-12

by HCFC-134a

of the compound

is (0.26

required

in the

values reported here agree between models reasonably well once accounting is in lifetimes, uncertainties in the values still exist due to the uncertainties in mo-

expect that these values will be updated

The HGWP

in replacing

must also be taken into account.

Although the HGWP made for the differences

hydroxyl

in HGWP

in calculated

Global

robust parameters

for the ultraviolet

reactions

We

and the

since their calculated

values are nearly

gases. The minor shifting of the HGWP values in primarily

lifetimes

their lifetimes Warmings

of these compounds.

compounds.

and therefore

the abundance

relative global warmings for halocarbons

on whether

the Relative

lifetimes

are shorter

asymptotically

in the atmosphere.

are initially on order unity but decrease

or longer than that of the reference approach

the HGWP

gas. At

values.

381

PRECEDING

PAGE

BLA_'K

NGT

FILMED

N92"15447

RELATIVE METHANES

EFFECTS ON GLOBAL AND ETHANES

WARMING

OF HALOGENATED

OF SOCIAL AND INDUSTRIAL

INTEREST

Donald A. Fisher and Charles H. Hales E.I. du Pont de Nemours Wei-Chyung

Wang,

Atmospheric

Malcolm

& Company

K. W. Ko and N. Dak Sze

and Environmental

Research,

_ING

Inc.

PAGE

BLI'.',_K NOT

FILMED

GLOBAL WARMING ABSTRACT The relative potential global warming effects for several halocarbons (CFCs -11, 12, 113, 114, and 115; HCFCs 22, 123, 124, 141b, and 142b; and HFCs 125,134a, 143a, and 152a; carbon tetrachloride; and methyl chloroform) have been calculated by two atmospheric modeling groups. These calculations were based on atmospheric chemistry and radiative convective models to determine the chemical profiles and the radiative CFC-11

processes.

agree reasonably

ences among

The resulting

relative

greenhouse

well as long as we account

results are discussed.

trace gas levels assumed.

Sensitivity

Transient

relative

of relative global

warming

for differences warming

warming

when normalized

between

modeled

to the effect of lifetimes.

values is determined

effects

Differ-

with respect

to

are analyzed.

1. INTRODUCTION A systematic environmental includes the potential effects for rising environmental

evaluation of replacements for fully halogenated chlorofluorocarbons (CFCs) of each replacement chemical on global warming. While the major focus

concerns

centers on the potential effects of long-lived

the role of these gases as contributors

to an enhanced

greenhouse

tion. This concern

is based on the ability of these gases to absorb

'window'

8 and 12/am.

between

First, a brief background The radiative

to establish

and thermal balance

infrared

primarily

surface and atmosphere

ozone,

also needs examina-

radiation

the role of these gases in the 'greenhouse

of planet Earth is established

and visible) solar energy to the Earth's

CFCs on stratospheric

or global warming

in the atmospheric

warming'

by balancing

phenomena.

the incoming

with the outgoing (infrared)

radiation

(UV from

the Earth's surface and atmosphere eventually being lost to space. Infrared energy is partially blocked at many wavelengths by naturally occurring gases such as carbon dioxide, methane, and stratospheric water vapor.

These gases absorb energy at fundamental

contributes

frequencies

characteristic

of their structure.

and is eventually

re-radiated.

tive balance

of the infra-red

cooling process.

Hence, the concern

significantly

impede infrared cooling of the Earth with a decrease in energy loss to space and a corresponding

increase

in the Earth's

The atmosphere

surface

'window'

between

However,

that increasing

change the radia-

CO2 concentration

will

temperature. 8 and 12/am is virtually transparent,

that absorb energy at these wavelengths, tially unimpeded.

Changing gas concentrations

This energy

to local warming

outgoing infrared

radiation

i.e. since few gases are present

passes through

both C-CI and C-F bonds have natural

vibrational,

the atmosphere bending,

essen-

and rotational

excitation frequencies in this infrared frequency range such that CFCs absorb the infrared energy to become very effective greenhouse gases. Their effectiveness as greenhouse gases is accentuated by their long lifetimes. is important

Since functional

to estimate

replacements

of these gases is determined

gases build up higher

tropospheric

tiveness

gases are the infra-red

of energy absorbed

there is yet another

concentrations.

within these intervals

Besides the influence

infrared

energy

in the window

their potential impact on global climate as part of this evaluation.

strated below, the effectiveness as greenhouse

may also absorb

Longer

in determining

i.e. the wave length intervals

lived

the effec-

and the amount

by each molecule.

on the infrared radiative

aspect of the radiative

importance

it

As will be demon-

in large part by their lifetimes.

Of fundamental

band strengths,

region,

fluxes at the top of the atmosphere

perturbations

from halogenated

compounds

and at the surface, -- namely the addi-

385

PRECEDING

PAGE

B' _'_'" "-',,,a

NOT

F:LMED

GLOBALWARMING tional heating to increase

induced

in the tropical

temperatures

considerable

significance

Candidate

alternatives

HFCs) or carbon,

upper troposphere

in this region.

Any change

and lower

for the tropospheric-stratospheric are composed

hydrogen,

and fluorine

hydrogen

which has the potential

near the tropopause

exchange

of either carbon,

chlorine

stratosphere

in the temperatures

water

region

is of

(hydrofluorocarbons

or

vapor.

and fluorine

(hydrochlorofluorocarbons

or HCFCs).

For simplici-

ty, both classes of compounds are referred to as hydrohalocarbons. Because they contain hydrogen, the hydrohalocarbons are subject to destruction in the atmosphere through reaction with hydroxyl radicals. This destruction

mechanism

pounds (see [Fisher of these gases). upper

factor

et al. (1989a)]

By contrast,

stratosphere.

a primary

leads to much shorter for a discussion

This paper examines

below,

their potential

the calculated

lifetimes

of the chemistry

the only known destruction

As will be shown in reducing

atmospheric process

the shorter

for the hydrohalocarbon

affecting

the atmospheric

of CFCs is through

atmospheric

lifetime

comlifetimes

photolysis

of HCFCs

in the

and HFCs is

to affect global warming.

greenhouse

effects of several one and two carbon halocarbons.

Esti-

mates of these effects will be quantified in terms of a relative potential to enhance global warming (halocarbons global warming sient relative

potential or HGWP). warming

effects

Sensitivity

to assumed

will be analyzed.

Table

1 Compounds

HALOCARBON

FORMULA

IUPAC

CFC-|

|

levels of trace gases will be examined.

Examined

in this Study

NAME

CC13F

METHANE,

CFC-12 CFC- 113

CC12F2

CCI2FCCIF2

METHANE, DICHLORODIFLUOROETHANE, 1,1,2-TRICHLORO1,2,2-TRIFLUORO-

CFC- 114

CCC1F2CC1F2

ETHANE,

1,2-DICHLORO-

CFC-115

CCIF2CF3

ETHANE,

CHLOROPENTAFLUORO-

HCFC-22

CHCIF2

METHANE,

HCFC-123

CF3CHC12

HCFC- 124

CF3CHCIF

ETHANE, ETHANE,

HFC- 125 HFC- 134a

CF3CHF2 CF3CH2F

ETHANE,

2-CHLORO-1,1,1,2-TETRAFLUOROPENTAFLUORO-

ETHANE,

1,1,1,2-TETRAFLUORO-

HCFC- 14 lb

CC12FCH3

ETHANE,

HCFC- 142b

CCIFECH3

HFC- 143a

CF3CH3

ETHANE, ETHANE,

1,1-DICHLORO-I-FLUORO1-CHLORO- 1,1-DIFLUORO-

CHF2CH3

ETHANE,

CC14

METHANE,

CCI3CH3

ETHANE,

HFC- 152a

TRICHLOROFLUORO-

CHLORODIFLUORO2,2-DICHLORO-1,1,

1,1, I-TRIFLUORO1, I-DIFLUORO-

CARBONTETRACHLORIDE METHYL CHLOROFORM

386

1,1,2,2-TETRAFLUORO-

TETRACHLOROI,I,I-TRICHLORO-

I-TRIFLUORO-

Tran-

GLOBAL WARMING Halocarbon

Global Warming

Potential

is based on a concept

similar to Ozone Depletion

Potential

and

is used to describe the relative potential of each halocarbon as a greenhouse gas. No attempt is made to calculate HGWPs for non-halocarbon gases such as carbon dioxide and methane. Because of the current atmospheric

concentrations

and spectral

locations

of the infrared

absorption

bands of these other gases,

calculated global warming is not a linear function with increases in their atmospheric concentrations. In contrast, a calculated warming is linearly proportional to concentrations of halocarbons. Thus, Greenhouse

Warming

Potentials

Two atmospheric Pont Central Radiative

modeling

Research

Convective

groups,

(Du Pont),

and methane

Atmospheric

have calculated

considered

would not be meaningful.

and Environmental HGWP

values

in the literature

This paper will discuss the definition

of HGWP,

Research,

for sixteen

gases. These

as well as examine

groups

used et al.

ozone (Fisher,

formula

et al., 1989a).

the basis for selecting

of the differences

and Du

1985, Owens

1 along with their chemical

for effect on stratospheric

by the two models and an examination

Inc. (AER),

(Wang and Molnar

in this study are listed in Table

names and are the same as evaluated

The results calculated results

dioxide

models that are described

1985). The halocarbons and IUPAC

for carbon

its definition.

and uncertainties

in model

is also presented.

2. DEFINITION

BASIS

Halocarbon Global Warming Potential (HGWP) is defined in a manner parallel to the definition of Ozone Depletion Potential. It is defined as the ratio of calculated warming for each unit mass of a gas emitted into the atmosphere relative to the calculated warming for a mass unit of reference gas CFC- 11. This definition was chosen as a representative measure of the potential of a compound to effect global warming for several reasons: (1) It provides

a measure

for each unit released

of the cumulative

into the atmosphere

effect on the radiastive

(3) It provides

a measure

effect of CFC-11

The first of these reasons

of the maximum

over its chemical

lifetime

(see below).

(2) The HGWP yields a single value for each compound

calculated

balance

calculated

rather than a time varying

multitude

effect of a compound

compared

in that it estimates

the cumulative

of values.

to the maximum

on an equal mass basis.

is perhaps

the most important

chronic effect

on global warming of each unit released. An illustrative test was performed which quantified the chronic effect from a single pulsed release of test gas into the atmosphere, analogous to a test on effect on stratospheric ozone (Fisher

et al.,

1989a). The test used the Du Pont model to calculate

over a 500 year time period

following

impulse

releases 387

of HCFCs

cumulative

global warmings

-123, -22, and CFC-11.

GLOBALWARMING 0.022

I

0.020

d

I

t

t

t

r

J

t

I

I_,

SPECIES

AREA (deg.*yr)

RATIO to CFC-11

HGWP

CFC-11 HCFC-22 HCFC-123

1.176 0.358 0.019

1.0 0.30 0.016

1.0 0.29 0.015

0.018 0.016 0.014

dts 0.012

(deg.

T I

K)

0.010

I

0.008

i

0.006

-

0.004

-

0.002

-

I

"\"

0.000

_'

0

I

I

20

40

I

60

i

" -7 ........

",

80

100

t

t

120

140

I

i

160

i

180

200

Year

Figure 1. Calculated Change in Surface Temperature kg of Specified Gas

The calculated following atmospheric

cumulative

warmings

are shown in Figure

the release and tails off with an exponential lifetime

of the species.

such an event echo the relative

a Pulsed Emission

having a time constant

As seen in the insert table, the time-integrated calculated

this is not surprising

of 5.0x10"

*9

1. For each case, the effect peaks very rapidly

decay function

values of the HGWP

Appendix A of Fisher et al. (1989a), greenhouse warming.

Following

warming

from steady state figures.

if the response

function,

equal to the following

Referring

to

g(t), is to represent

3. DEFINITIONS

In order to make the definition of HGWP consistent between of relative effects, the following criteria have been selected: 1) Trace gas levels -- Changing

the concentration

models as well as a conservative

of other trace gases will affect the calculated

estimate

future

equilibrium temperature rise from gases under evaluation here for two reasons. First if there is overlap of absorption spectra, certain bands have less effect. Secondly, chemistry and therefore lifetime can be 388

GLOBALWARMING affected by perturbation of these chemicals. Current levels of CO2, CH4, N20, 03 and stratospheric H:O were used in model calculations. Sensitivity of this assumption will be tested in a following section. 2) Gas perturbation responses

levels -- Atmospheric

large enough to avoid the "noise

concentrations levels"

of the test gases were chosen

of the numerical

to yield model

models and still be in a linear response

region. 3) Reference gas -- CFC-11 has been chosen as the reference compound er to have a reference material consistent for both HGWP and ODP. 4) Specific

Surface Temperature

Change

-- We define the calculated

for HGWP calculations

surface

a one part per billion surface increase of any gas to be specific surface temperature

in ord-

temperature

increase

for

change,

or symbolical-

ly dT s. The HGWP

definition

resembles

Calculated

IR forcing

Calculated Emission IR forcing

Since radiative

IR forcing

is the net change

convective

to (moleculear

[dTs(CFC

can chemically

influence

a surface

change

approximately

below) and since lifetimes are proportional

* emission

rate), an equivalent

proportional

to the ratio of atmospheric

form of this definition

is:

11)/Molecular

the distribution

of affecting

weight(CFC heating

11)]

rates indirectly

as well since they

of ozone which would affect both the solar and the long wave

of model results indicates

that this is a second

order

effect,

of these calculations

at least two (Wang et al.

1989).

CALCULATIONS

appropriate

input to these radiative chemistry

Once the concentration vective

temperature

below the IR effect and well below the sensitivity

communication,

The primary using

X

in IR flux at the tropopause.

11) * Lifetime(CFC

rates. An examination

orders of magnitude

4. MODEL

X/

state) of CFC-11

Note also, many of the gases have the potential

private

is:

due to CFC-11/

models calculate weight

definition

[dTs(x) * Lifetime(x)/Molecular weight(x)] ............................................................................

HGWP

heating

Thus for any gas, the general

due to Compound

rate (steady

to the IR forcing level (to be examined abundance

definition.

Emission rate (steady state) of Compound ........................................................

HGWP

Note:

the ODP

model.

calculations

are the altitudinal

steady-state

concentration

profiles

models.

profile is determined,

These models utilize infrared

the effect of each gas is calculated absorption 389

spectra to quantify

using a Radiative

Con-

a gas's ability to absorb

IR

GLOBAL WARMING

Table 2 Total Rogers

Varanasi

Gehring

Chudamani (1988)

et al. (1983)

(1987)

CFC-11

2389

2566

CFC-12 CFC-113

3364

4822

3267 3507

CFC-114

5935

3937

Stephens (1988)

&

of Halocarbons

Kagann

Species

&

Band Strengths

Magid + (1988)

2389* 3310 3126

3240* 3401" 4141"

CFC-115

4678*

HCFC-22

2399

2554*

HCFC- 123

2552

2859*

HCFC- 124

4043*

HFC- 125 HFC- 134a

3908* 3169

3272*

HCFC-141b

1732

1912"

HCFC- 142b

2474 3401"

2577*

HFC- 143a HFC- 152a

1648" 1195"

CC14 CH3CC13

1184

1209"

* Infrared data used in model calculations + The IR data from Magid tegrated

energy

band strengths

and thereby accounts

were given with spectral

impact the earth's

that the solar heating culation

(1988)

resolutions

are given here so that they can be compared

is balanced

heat balance.

by the infrared

for the amount

of energy

Equilibrium

temperature

cooling at all altitudes

absorbed

of 0.5 to 0.25 cm -1. The in-

to other data.

profiles are calculated

through

the atmosphere.

by each IR gas (the band strength)

such

The cal-

at specified

wavelengths (the band location) including spectral overlap with other IR gases. Quantitative infrared data for this input are available from literature sources for the CFCs (Kagann et al. 1983; Varanasi and Chudamani, 1988; and Rogers and Stephens, from industry

laboratories

Total band strengths the exception

(Magid

available

1988) and measurements 1988, and Gehring for these calculations

and the HFCs were obtained

as shown

in Table 2 are within about

of Rogers and Stephens (1988). The band strengths used for the model calculations

with an asterisk.

Since there appear to be systematic

measurements,

the values from a common

the compounds

of interest in this study. For compounds

(1987)

for the HCFCs 1987).

differences

between

data base [Magid (1988)]

was used. 390

not available

laboratories

10% with are marked

for band strength

were used since it covered from this source,

most of

data from Gehring

GLOBALWARMING

0

_J

6

6 >.,

U3 (-

°J

6

U3

03 "O

A

Cs_ e

d

_E O

co



,m

3.0

2.5

CFC-12

2.0

1.5

1.0

0.5

0.0

....

0

F ......

50

t ....

100

P ....

150

-_- .....

200 Time

Figure 4. CalcuLated (CFC-11 Reference)

Relative Warming Following [Du Pont 1-D Model]

399

I.....

250

I......

300

_....

350

ff .....

400

450

(Yrs)

a Step

Change

of Emission

of Specified

Gas

GLOBAL WARMING

(Du Pont 0.12

1-D Model)

t

I

t

I

I

I

•/J

0.11 4.p , ,.z• " ""

0.10 J

/.

f

*

f

0.09

/"

p p

•/ /"

,/ /

/'"

/

0.08

//

/, j J /

I ./t

/ /

// //

_f'

0.07

//

/. i""

dTg 0.06 (deg K) /p#'

0.05

p j p

,"

/" ,/"

//

0.04f

i"

.....

0.03 0.02 0.01 0.00 -10

I

I

I

I

I

I

I

I

I

I

0

10

20

30

40

50

60

70

80

90

100

Time

(Yrs)

with

various

CFC-11 CFC-12 ...................HCFC-22 ..... HCFC-123 .......... HCFC-141b .............. CFCl15 No Replacement

Figure 5. Transient Calculated species at t = 0 and constant

Global Warming; emission.

400

Ib/for/Ib

replacement

of CFC-11

GLOBAL WARMING the relative amount in the atmosphere, the relative effects either grow or decrease depending on whether the lifetimes are longer or shorter than that of CFC-11. As seen in Figure 4, the HCFCs have lifetimes shorter

than the lifetime

of the reference

HGWP

value with a time constant

gas and have relative

equal to the lifetime

effects that grow with time asymtotically OWN lifetime. Another perspective transitions

approaching

warming.

Longer

their HGWP

ing from substitution

for CFC-11

lived species

of compounds

were meant to estimate

were used,

are substituted

of THEIR

and the resulting

the warming

scenarios changes

per-

result-

level and growth (in atmospheric

namely 260 pptv and 4.0%/yr.

on an equal mass basis. Results

the

have relative

value with time constant

of various gases for CFC-11 at time, t = 0. Current

Compounds

approach

Figure 5 shows the results of a simple set of substitution

formed using the Du Pont model. These calculations

constant.

of CFC-11.

on the transient response is to consider the replacement

in calculated

concentrations)

effects that asymptotically

Emission

levels were assumed

for all HCFCs

fall within the enve-

lope bounded by the no replacement results and the results for continued emission of CFC-11 and show a negative trend in warming within a few years of substitution. Results for CFC-12 and CFC-115 on the other hand show continued

positive

slope exceeding

the CFC-11

no-substitution

case for all times.

UNCERTAINTIES Uncertainties

in the the effectiveness

-- those that are generalized species There

considered

radiative properties temperature

to the total greenhouse

of problems

that need to be resolved

need to be quantified

structure of the atmosphere of oceans

which

Uncertainties balance. profiles

also exist regarding

Research

of questions

ing and magnitude

of continuing

HCFCs,

of surface

warming.

patterns and chemistry to surface

warming.

balance

of individual affecting

species

The

and changes

Changes

in the

of the stratosphere.

temperature

changes

will also

to understand

these

of the earth.

and HFCs and their influence

The chemical processes

on the radiative

need to be resolved

both lifetimes

and

and atmospheric

research.

related to the general greenhouse

of global warming,

of greenhouse

is being carried out worldwide

of the absorptances

for use in climate models.

for halocarbons

and ocean currents

the CFCs,

dependence

are also the subject

Resolution

classes

to the individual

in the surface and ice cover albedos, as a function

apply to ALL trace gases that affect the future radiative

The temperature

parameterized

fall into two general

that are specific

in the modeling

will affect the convective

(as heat reservoirs)

affect the timing and location of the warming. questions

effect and those

of the earth's surface such as changes

and composition

The coupling

global warming

here.

are a number

in cloud cover

of gases to produce

whereas resolution

will have a direct effect on the HGWP

warming

will directly affect the modeled

of the radiative

and chemical

tim-

parameterizations

values for these species.

7. ACKNOWLEDGMENTS The authors are grateful for the support received bon Environmental

Acceptability

for this work from AFEAS,

Study).

401

(Alternative

Fluorocar-

Xo

IMPACT ON PHOTOCHEMICAL INCLUDING TROPOSPHERIC

An Assessment

of Potential

lmpact

of Alternative Hiromi

Fhu_rocarbons

OXIDANTS OZONE

on Tropospheric

Ozone

Niki

Centre for Atmospheric Chemistry Department of Chemistry York University 4700 Keele Street, North York Ontario, Canada M3J 1P3

PRECEDING

PAGE B;..;:.;,_K Nor

FILMED

TROPOSPHERIC OZONE EXECUTIVE One type of tropospheric tion as precursors assessment 1.

the following

specific

On a global

halocarbons

may arise from their possible

of 03 and other oxidants on urban issues related

Is it likely that the HFCs and HCFCs in the vicinity

2.

impact of the alternative

to the formation

SUMMARY

to tropospheric

would contribute

and global scales.

contribu-

In the present

oxidants are addressed: to production

of photochemical

oxidants

of release? basis, how would emissions

of HCFCs

and HFCs

compare

to natural

sources

of 03

precursors? Since almost all CFCs are emitted in urban environments,

the first question

deals primarily

with urban

"smog" formation, Salient features of chemical relationships between oxidants and their precursors as well as the relevant terminologies are described briefly in order to provide a framework for the discussion of these two issues. Based on an analysis of the atmospheric reactivity

and 03 forming

to 03 production

potential,

concentrations

the maximum

in both urban and global atmospheres

1: Urban Atmosphere

(values in parenthesis

HFCs:

CH3CHF2-152a

HCFCs:

CHC1F2-22

2: Global Atmosphere

(59), CH2FCF3-134a

HFCs:

CH3CHF2-152a

HCFCs:

CHC1F2-22

CH3CCI2F-141b

(8), CHF2CF3-125

fluorocarbons

as follows: of all 03 precursors):

(4) (16),

(59)

in units of 10 -3% of the total contribution

(92), CH2FCF3-134a

(11), CH3CC1F2-142b

and their atmospheric

of the alternative

have been derived

(6), CH3CHC1F-124

(13), CHCICF3-123

(values in parenthesis

03 precursors,

contributions

in units of 10-3% of the total contribution

(8), CH3CC1F2-142b

CH3CC12F-141b

of various

projected

(11), CHF2CF3-125 (10), CH3CHCIF-124

(20), CHCICF3-123

of all 03 precursors):

(7) (25),

(92)

405

PRE'C.EOING

P.-,,_,.Jr_.'_'C

B_.,'_'..._K :_' NOT

F;_L_'FZ)

N92-15448

ASSESSMENT

OF POTENTIAL

IMPACT OF ALTERNATIVE TROPOSPHERIC OZONE

FLUOROCARBONS

ON

Hiromi Niki

Centre for Atmospheric

Chemistry

Department of Chemistry York University 4700 Keele St., North York Ontario,

Canada

M3J

1P3

PRECEDING

P',_GE Bi._':.i,_K NOT

F_.ML_

TROPOSPHERIC OZONE 1. INTRODUCTION While

the chlorofluorocarbons

inert in the troposphere,

(CFCs)

such as CFC-11

the hydrogen-containing

to a large extent, be removed

halocarbons

in the troposphere

and CFC-12

(CFCI3)

being considered

by the HO radical.

(CF2CI2)

chemically

are

as their replacements

These alternative

halocarbons

can, include

the hydrochlorofluorocarbons (HCFCs) 123 (CF3CHCI2), (CHF2CI) and 124 (CFaCHFC1) and the hydrofluorocarbons

141b (CFCI2CH3), 142b (CF2C1CH3), 22 (HCFs) 134a (CF3CHEF), 152a (CHFECH3)

and 125 (CF3CHF2).

(k) for the HO radical reaction

pounds

[Hampson,

Listed in Table 1 are the rate constants Kurylo and Sander,

1989] and their estimated

chemical

lifetimes

of these com-

in the troposphere

[Prather, 1989; Derwent and Volz-Thomas, 1989]. In this table, values of the lifetimes of these selected HCFCs and HCFs are seen to vary by more than a factor of more than ten ranging from 1.6 years for HFC

152a and HCFC

or minimizing alternates.

125 to as long as 28 years for HFC 125. Clearly,

impact on stratospheric

However,

be assessed

and taken into account

One type of tropospheric tion as precursors assessment 1.

specific

with short tropospheric

consequences

in the selection

impact of the alternative

to the formation

the following

of their degradation

of avoiding

lifetimes are the desirable in the troposphere

should

process. halocarbons

of 03 and other oxidants issues related

Is it likely that the HFCs and HCFCs the vicinity

2.

03, those halocarbons

potential environmental

from the standpoint

on urban and global

to tropospheric

would contribute

may arise from their possible oxidants

to production

scales.

contribu-

In the present

will addressed: of photochemical

oxidants

in

of release?

On a global basis,

how would emissions

of HCFCs

and HFCs

compare

to natural

sources

of Oa

precursors? Since almost all CFCs are emitted in urban environments, "smog" formation. and their precursors a framework

the first question deals primarily

In the following section, salient features of chemical as well as the relevant terminologies will be described

for the subsequent

report deals only with possible

discussion

of these two issues.

direct chemical

with urban

relationships between oxidants briefly first in order to provide

It should be mentioned

that the present

effects and not with indirect climate-chemical

interactions

[cf. Wang 1986; Ramanathan et al. 1987; Wuebbles et al. 1989]. Namely, the alternative halocarbons and/or their degradation products may act as "green-house" gases and alter the global tropospheric 03 distribution cussed

via changes

elsewhere

in climate and emission

in the AFEAS

rates of natural

precursors

of 03. The latter topic is dis-

report.

2. BACKGROUND 2.1. Photochemical

Oxidants

The present assessment deals specifically with issues concerning 03 rather than "oxidants" The term "oxidant" is often used loosely and deserves clarification. Very often, it refers

in general. implicitly to

03, the most abundant oxidant in the troposphere. However, there are many other trace atmospheric gases which are also known as "oxidants," e.g. hydrogen peroxide (H202), peroxyacetyl nitrate (PAN), and formic acid (HCOOH).

As already discussed

elsewhere

in the AFEAS

report [cf. "Degradation

Products

409

PRSCEDING

P._,GE 13t ,_.,_:, ,.r.,v NOT

F!LMED

TROPOSPHERIC

OZONE

Table

1 Rate

Constants

for

the

HO Reaction

of

Alternative

A-Factor Compound

Fluorocarbons

k(298

x 10 -lz

E/R

K) (a)

x 10 "Is

Lifetime

(d)

(yr)

HFCs (b) CH3CHF2

152a

1.20

1100 + 200

37.0

1.7

CH2FCF3

134a

1.70

1750_+300

4.8

13.2

CHF2CF3

125

0.38

1500 _+500

2.5

25.4

22

1.20

1650 _+ 150

4.7

3.5

CH3CC1F3

142b

0.96

1600_+

150

3.8

16.7

CH3CHCIF

124

0.66

1205 _+300

10.0

6.3

CH3CCI2F

141b

0.27

1050 _+300

8.0

7.9

CHC12CF3

123

0.64

850 _+ 150

34.0

1.7

0.15

0 _+300

150.0

CH4

(1 +0.6 Patm) 2.30

1700 _+200

C2H6

11.00

1100 + 200

CH3CCI3

5.00

1800 _+200

HCFCs

(b)

CHCIFz

(a) k in cm 3 molecule from

Hampson,

(c) Taken

from

NASA

(d) Lifetime

=

1981)

et al.,

Patm) 7.7

280.0 12.0

8.2 0.2 5.3

-_ s -_

(b) Taken

Volz

(1 +0.6

0.3

1/k[HO];

Kurylo

Kinetic

Data

and

Sander

(AFEAS

Report,

1989)

(1987)

k at 298 K; [HO]

taken

to be 5xlO 5 molecule

410

cm -3 (Crutzen

and Gidel,

1983;

TROPOSPHERIC OZONE of Alternative of a variety oxidants

Fluorocarbons of products

derived

in the Troposphere"],

which can be considered

from the alternative

and their potential

tropospheric

the alternative as "oxidants."

halocarbons

halocarbons

can lead to the formation

Some of the halogen/carbon-containing

may play important

roles in atmospheric

environments

impact must be assessed.

Broadly speaking, the term "oxidant" simply refers to the oxidizing ability of a reagent, i.e. to remove electrons from, or to share electrons with, other molecules or ions [Finlayson-Pitts and Pitts, 1986]. The ability of a chemical and is expressed

species

to oxidize or reduce

in volts. For example,

other chemical

03 has a standard

species

potential

is termed

its "redox

potential"

of + 2.07 volts in the redox pair of

O3/H20, and hydrogen peroxide + 1.776 volts in the redox pair, H202/H20 [Weast, 1977]. Historically, the term "oxidant" has been defined by a wet chemical technique; that is, an oxidant is any species giving a positive

response

ion in solution

in the KI method.

to form brown

The basis of this method

2H + This technique of measuring In addition, the U.S. Federal oxidant

is the oxidation

of the colorless

iodide

12: + 2I- + 03 --' I2 + 02

+ H20

and reporting total oxidants was used almost exclusively until the mid- 1970s. Air Quality Standard was written in terms of "total oxidant" (0.08 ppm

for 1 h) rather than 03 specifically.

A variety

of air pollutants

give a positive

response,

but some

interfere negatively. Namely, "total oxidants" will include a weighted combination of various pollutants such as 03, NO2, and PAN, but SO2 gives a 100% negative response and must therefore be removed with the use of a scrubber, The recognition

e.g.

of the problems

of physical

techniques

Air Quality

Standard

from the gas stream

Cr203,

with the wet chemical

for monitoring from oxidant

the major oxidant the UV method

air, and is accepted

method"

as an "equivalent

the term "photochemical ticular context. 2.2 Ozone

below.

and the simultaneous

03 specifically, the standard

led to a change was relaxed

is most commonly

in a species-specific

in the Federal

to higher

used to monitor

by the EPA [Finlayson-Pitts

must be defined

development concentra-

03 in ambient

and Pitts 1986]. In any case,

manner

depending

upon the par-

Precursors

Within the context monoxide

oxidant"

to analysis.

KI technique

to O3; simultaneously

tions, 0.12 ppm 03 for 1 hr. Today,

prior

of the present

and various

Namely,

assessment,

volatile organic

the term "ozone

compounds,

it is now well-established

particularly

that significant

precursor"

can be equated

hydrocarbons,

in-situ photochemical

with carbon

for reasons

stated briefly

production

and destruc-

tion of 03 takes place on urban, regional and global scales [WMO 1985; Logan 1985; Finlayson-Pitts and Pitts 1986; Crutzen 1988]. Tropospheric 03 production occurs via carbon monoxide and hydrocarbon oxidation,

with NO x ( = NO + NO2) acting as a catalyst.

species participate ed as:

interactively

in these chemical processes.

HC + NO x + hv _ where

HC denotes

various

reactive

03

carbon-containing 411

of molecular

and free radical

The overall reaction mechanism

A large number

can be represent-

+ other products compounds,

particularly

(1) hydrocarbons,

and hv is

TROPOSPHERIC OZONE solar radiation production lowed

reaching

the earth's

of 03 is due entirely

by the recombination

surface

in the wavelength

to the photodissociation

nm) --* NO

O + 02 + M --*03 M is any third body,

03. Thus,

strictly speaking,

O atoms are the primary in reaction NO

Reactions

2-4 alone do not provide

formation

and destruction

+

3

the energy

precursor

of the reaction

and stabilizes

of 03. NO2 can act as both the source

03 and regenerates

NO2:

NO2 + 02

_

of 03, thus establishing

(3)

(4)

of 03 but are largely

responsible

a steady 03 concentration

for controlling

governed

the

by the so-called

state relation,

where k is the rate constant

attributed

0

(2)

+ M

2 removes

a net production

[03]

According

+ O

such as 02 and N2, that removes

and sink for 03, since NO produced

photostationary

into NO and O fol-

of O with 02: NO2 + hv(_ Urn. 439

than

sea-salt

and

aerosols. Comment

the

of Kritz

of considerably

in the flux of sea-salt

Ma-

Wilkniss and Bressan (1972) Wilkniss and Bressan (1972) Chesselet et al. (1972) Peirson et al. (1974) Wada and Kakabu (1973) Buat-Menard et al. (1974) Martens eta]. (1973) Kritz and Rancher (1980) Parungo et al. (1986) Vong et al. (1988)

those

NATURAL SOURCES Robbins

et al. (1959)

suggested

that aerosol

NaC1 + 2NO2 Thus nitrosyl chloride

(NOCI)

chloride

could react according

--* NaNO3

+ NOCI.

(R1)

would be the form in which the chlorine

bins et al (1969) noted that NOCI would rapidly hydrolyze

to

is released

in the atmosphere

from aerosol.

to form HCI. This mechan-

ism is deemed unlikely now (cf. NRC, 1975). Eriksson (1959), and Duce et al. (1973) assumed gaseous inorganic chlorine is most likely to be HCI which is released via H2SO

Hitchcock

4 +

2NaCI --* (sea-salt)

et al. (1980) found high correlations

Na2SO4

between

(R2)

Cl-depletion

in filter samples of aerosols collected on the coast of North Carolina confirmation of Eriksson's hypothesis of R2. Clegg and Brimblecombe

(1986) have shown that Henry's

that the

2 HC1.

+

Rob-

and excess (non-sea

and interpreted

law considerations

salt) SO42-

their findings as strong

involving

equilibrium

be-

tween gaseous HC1 and the aqueous ions indicate that reaction R2 or any similar reaction involving a mineral acid that is less volatile than HC1 goes essentially to completion for relative humidities below 98 %. In respect to the atmosphere, this means that HNO3 can release HC1 as well as H2SO 4. Thus to explain the release of gaseous HC1 to the atmosphere when the primary sea salt particles dehydrate, R2 can be rewritten as H ÷ + NaC1 _ (sea-salt)

Na ÷ + HCI.

(R3)

In this equation, it must be understood that the hydrogen ion is supplied by acids of lower volatility than HC1 and that for the atmosphere H2SO4 and HNO3 are the most abundant species available for the task. Given the observations that the degree of chlorine depletion of sea salt aerosols is generally less than 20%, it is clear that the gaseous and aerosol forms of HCI are not in equilibrium, even over the oceans. The mechanism

represented

by R3 has received

considerable

support

from the recent work of Legrand

and Delmas (1988) who examined the results of several ice core (Delmas et al. 1982, Legrand and Delmas, 1984, 1985) and air sampling programs (Duce et al., 1973 and Maenhaut et al., 1979) in Antarctica concerning

chlorine.

They used ion balances and calculated acidity for two circumstances

1. When C1- is in excess of Na + relative

to bulk sea water:

[H ÷] = IxsSO4 =] 2. When CI- is depleted

relative

as indicated below.

+ [NO3-]

+ [xsCl-].

to Na ÷ :

[H ÷] = [xsSO4 = ]a + [NO3-], where [xsSO4 = ]a is the portion of excess not been neutralized by the above reaction. This system thus assumes

that when C1- is in excess the reaction

extent, whereas when CI- is depleted the reaction has proceeded 440

has not proceeded

toward completion

sulfate that has

to an important

leaving some unneutral-

NATURAL SOURCES ized xsSO4 = behind to contribute equivalent sulfate

concentrations,

its acidity (thus the subscript

is that which cannot be ascribed

from sea-salt.

The original

sea-salt

to sea-salt

contents

sea water. The excess sulfate is considered SO4 =. The difference

a). All quantities

which is the reason there is no factor of 2 preceding

between

based on the assumption

are assumed

in brackets

that all of the sodium comes

to have the same relative

to be the result of the conversion

are chemical

the sulfate terms. Excess composition

of gaseous

the total excess sulfate and xsSO4 = a represents

as bulk

SO2 to particulate

the amount

by which the

C1- is depleted. Legrand

and Delmas

(1988) used the above model and the observed

NO3- and C1- in the ice cores to calculate

concentrations

the acidity which they then compared

of Na + , SO4 =,

to the observed

H +. The

agreement was very good for the two-hundred year period (a 16m long ice core) studied in detail. All of the major features and most of the minor variations were very closely in agreement. The model was able to account for the acidity during prolonged to Na +. The authors from sea-salt suggest

could

not state with certainty

since volcanoes

that the aerosol

periods when CI" was both in excess and in deficit relative

and other sources,

that the HC1 (i.e.,

including

source is the most likely one to account

sion and permits

a useful

From a global perspective, and nitrogen excess sulfate

of reactive

of reaction

is from pollution

chlorine

sources,

R3 represents

data. A glance at Table

Legrand's

an important

to be much

and Delmas'

link between

cycle on the other because,

in the troposphere.

the amounts

they

conclu-

cycle.

cycles on the one hand and the chlorine

it may be the main source by human

the operation

entirely

However,

from sea salt is estimated

This then supports

view of the global chlorine

are known.

for the Antarctic

1 shows that even at the lower limit, the flux of gaseous C1 derived larger than the sum of all of the known other sources.

the xsCl-) was derived

human activities,

as shown in Table

Over continents

of HCI released

the sulfur

where

must be considered

1,

much of the to be affected

activities.

e. The organic

chlorine

The most abundant

source

natural

chlorine

which has its origin in the oceans.

containing

is the source of CH3I. of biological processes forward to estimate and tropospheric

its iodine atom for a chlorine

that of the surface

water and in the air over the oceans.

oceans.

Lovelock

its flux into the atmosphere

Zafiriou

atom in the laboratory that biomethylation

CH3C1 (1975)

at tempera-

CH3I also has been found in low concentrations et al. (1973) suggested

based on measured lifetime.

Other organic

(cf Burreson et al., 1975) but their concentrations

as sources of atmospheric of active chlorine concentrations.

is methyl chloride,

in ocean

of I in the oceans

So it is possible through the exchange reaction that CH3CI is a secondary product in the oceans. Despite the uncertainty of the origin of CH3C1 it is relatively straight-

air and on its tropospheric

in marine organisms

in the atmosphere

The details of its source in the oceans are not known.

has shown that CH3I readily exchanges tures approximating

molecule

chlorine.

in the stratosphere

Finally it is noteworthy

concentrations chlorine

have been found

are so small as to be entirely negligible

that CH3C1 represents

which in turn represents

in surface ocean waters

molecules

a natural

regulator

the major natural

source

of stratospheric

ozone

f. The cycle and its balance From the above discussion of atmospheric

chlorine

of chlorine

sources

it is clear that the oceans are the overwhelming

and that the bulk of atmospheric 441

chlorine

source

exists over the oceans in the forms of

NATURAL SOURCES aerosol

derived

from sea salt and gas, probably

both forms of chlorine rine is deposited over the oceans.

by transport

HC1, released

from the marine

from the aerosol.

atmosphere.

The continents

receive

About 90% of the sea-salt derived

chlo-

back into the oceans. Thus it is seen that most of the atmospheric chlorine cycle operates The 10 % of chlorine transported to the continents is deposited on the surface from which

it finds its way to rivers and streams and back to the oceans. Recent studies indicate that there may be significant aerosol chlorine contributions by forested areas. The possible release of gaseous chlorine from the plant derived dustrial

regions,

presumed

aerosol

has not been investigated.

to be of anthropogenic

The amounts

Chlorine

in excess of that which can be ascribed

of chlorine

in Table 1 represent

found in continental

to sea salt (relative

air, particularly

in in-

to sodium) has generally

been

origin.

injected

into the atmosphere

a forced balance.

The magnitude

in sea salt and the amounts

of the uncertainty

deposited

as given

of sea salt source strength

makes

it is possible that a secondary source, such as forests might make a significant contribution to natural chlorine in continental air. This is a subject for further investigation. We can judge the consistency of the cycle by using the estimates of Cl-deposition tion over continents to estimate the average served concentrations.

Table 3 provides

in precipitation on continents and the known total precipitaC1 concentrations in precipitation and compare them to ob-

the necessary

information.

The precipitation

Werby (1958) for the United States (mid 1955 - mid 1966) were selected because in extent and are less affected by pollution than subsequent surveys. The relatively tween the calculated

and observed quantities

listed in Table 3b reflect consistency

of the cycle. That is to say that there appear

to be no unknown

significantly

by the rather

alter the balance

as represented

sources

generous

data of Junge

in the quantitative

or sinks of chlorine

ranges in Table

the ranges of uncertainty

components

global average

cycle. Obviously

lacking are reliable

aspects

that could

1. However,

clear that there is much more insight to be gained by narrowing of the chlorine

and

they are continental close agreement be-

it is

in the various

values of concentrations

in air and precipitation.

Table 3a. Fluxes

of water

and chlorine

Precipitation over continents CI deposition

Table 3b. CI concentration

(Tg yr "_)

9 x 107 520 - 1500

(ppm) Calculated

from above

Observed

6 - 17

Precipitation

0.1

-

8a

Reference: a. Junge and Werby (1958)

The Fluorine Cycle Most of the fluorine and 0.09%

in the earth's

crust is in solid mineral

by weight of the upper layers of the lithosphere

borne soil dust can and does contribute The abundance

of fluorine

ships among the dissolved

to the atmospheric

form where (National

burden

it constitutes

Research

Council,

between

0.06%

1971). Wind-

of fluorine in the form of soil minerals.

in the oceans is 1.3 ppm by weight and is controlled

by equilibrium

relation-

species F-, MgF +, CaF +, and NaF and the solids MgF2 and CaF_. The mass 442

NATURAL SOURCES ratio of F/C1 in seawater as it is for chlorine. mosphere

is 6.7 X 10-5. The marine

The question

aerosol

arises as to what extent,

is therefore

a source of atmospheric

if any, gaseous

fluorine

fluorine

is released

to the at-

from the sea salt aerosol.

Cicerone

(1981) noted in his review that there is virtually no quantitative

in the atmosphere. concerned

Barnard

with fluoride

and Nordstrom

in precipitation.

(1982) have reviewed

information

about natural fluorine

most of the prior work, which is mainly

The work of Symonds,

Rose and Reed (1988) provides

a new

perspective for the role of volcanoes, albeit the flux estimates range over an order of magnitude. In contrast to the case of chlorine, volcanic activity could be the most important natural source of gaseous fluorine, most likely in the form of HF. Symonds, Rose and Reed (1988) give estimates of various emission rates for natural and anthropogenic sources of fluorine. These estimates along with information from Erickson and Duce's

(1988)

study of sea-salt

Table 4. Global Atmospheric

flux are incorporated

Fluxes

in Table 4.

of Fluorine

Natural F(sea-salt) HF(g)

to atmosphere:

0.4-

sea salt to atmosphere:

HF (g) volcanos

0-

to atmosphere:

1 Tgyr -_ 1 Tg yr "l

0.06 - 6 Tg yr -1

Soil dust to atmosphere:

400 mg/kg (> 2.9 mmol/kg)

(Rosenberg,

sodium

Several

LD50 values have been

trifluoroacetate

1971), > 2000 mg/kg (>

intraperitoneally,

14.7 mmol/kg)

(Airak-

sinen and Tammisto, 1968), > 5000 mg/kg (> 37 mmol/kg) (Blake et ai., 1969), and > 2000 mg/kg (> 14.7 mmol/kg) (Airaksinen et al., 1970) were obtained. TFA itself produced death in two of five mice treated intraperitoneally et al.,

at 150 mg/kg (1.1 mmol/kg),

1969). The LDs0 of sodium trifluoroacetate

probably

as a consequence

when administered

intravenously

of its acidity (Blake to mice was 1,200

mg/kg (10.5 mmol/kg) (Airaksinen and Tammisto, 1968). Preadministration of phenobarbital (40 mg/kg/day) for three days, or L-cysteine, isoniazid, ethanol, 4-iodopyrazole, or allopurinol administration 10 min before and 3 hr after sodium triftuoroacetate administration did not affect its LDs0, suggesting that the acetate was not being metabolized to toxic products (Airaksinen et al., 1970). Acute lethalities of the ord456

BIOLOGICAL ANDHEALTHEFFECTS er reported

for TFA, categorize

points, primarily

it as a "slightly

toxic" substance

(Klaasen

et al.,

1986). Other toxic end-

involving effects on metabolic activity, have also been investigated.

Sodium trifluoroacetate

in saline was administered by a single injection intraperitoneally to Swiss, albino, (Rosenberg, 1971). By 12-hr after administration of 2000 mg/kg (14.7 mmol/kg) the coenzyme

NADPH

in the liver was statistically

significantly

decreased

The decreased levels returned to normal by 24-hr after administration levels in the livers were also statistically after administration

significantly

and by 24-hr these levels

decreased

male mice (17-20 g) the concentration of

from 0.44

(Rosenberg,

to 0.25 /_mol/g.

1971). Reduced glutathione

from 4.33 to 3.94/_mol/100

had also returned

to normal

(Rosenberg,

mg at 12-hr 1971).

Male Wistar rats (200-260 g) were administered TFA in the drinking water for 5-6 days, equivalent to a dose of 150 mg TFA/kg body weight/day (1.3 mmol TFA/kg body weight/day) (Stier et al., 1972). In TFA-treated content

rat liver relative

decreased

by 24%,

to untreated

the neutral

rat liver, the soluble protein

fat increased

by 43 %. None of these effects were evaluated in liver of TFA-treated

animals

was altered

increased

by 6%, the glycogen

by 10% and the percent liver weight to body weight

for statistical relative

significance.

to control

A number of enzyme

rat livers:

pyruvate

kinase

activities

decreased

by

42 %, phosphoglycerate kinase decreased by 10 %, glycerol l-phosphate oxidase increased by 125 %, glycerolphosphate dehydrogenase decreased by 4%, malic enzyme increased by 4%, glucose 6-phosphate dehydrogenase decreased

decreased

by 17%, glyceraldehyde

by 7%, malate dehydrogenase

and NADPH-oxidase

increased

3-phosphate

decreased

dehydrogenase

by 10%, isocitrate

by 7%. Again differences

effects

studies TFA has been administered

which

were sought.

However,

to animals,

week-old

male Alpk/AP

(0.09 or 0.22 mmol/kg) changes

but without

producing

attempt

strain rats (Lloyd et al.,

were noted in the testes

relative

When TFA (240 mg/kg, or small intestinal

2.1 mmol/kg)

by 10%

significance

kinase and glycerol

the certain

specific a no ad-

in a single dose to ten-

1988; Lloyd et al., 1986). At doses of 10 or 25 mg/kg

to untreated

controls

(Lloyd

and 2,2,2-trifluoroethanol histologically-detectable

was administered

intravenously

1986).

to male Wistar

rats no bone

of TFA, 2,2,2-trifluoroethanol and 2,2,2-trifluoroacetaldehyde, at equimolar doses produced decreases in intestinal dry weight and leukocyte counts (Fraser and Kaminsky, 1988).

significant

(7.4 mmol/kg) Wahlstrom,

intraperitoneally

and killed 24 hr later, at 2000 mg/kg

2000 mg/kg (14.7

mmol/kg)

every

and Kaminsky,

1988; Lloyd et al.,

significantly reduced body weight testicular damage.

precursors

g) were injected

(Fraser

et al.,

and no histological

1988). The metabolic

Swiss male mice (17-20

toxicity was detected

decreased

made to determine orally

body weight gains and relative testis weight were not affected,

Equivalent doses of 2,2,2-trifluoroacetaldehyde gain and relative testis weight, and produced

marrow

of pyruvate

in water and administered

by 4%, enolase

for statistical

exception

there has been no systematic

verse effect level for TFA. TFA was neutralized

dehydrogenase

were not evaluated

and it is doubtful whether any of the activities, with the possible 1-phosphate oxidase, were significantly affected. In several

decreased

(14.7 mmol/kg)

strom,

1971). There were no TFA-induced

1971). However,

at 1000 mg/kg

and killed at 12 or 24 hr later, at

second day for 14 days and killed on the 14th day (Rosenberg histological

treated mice. At the lowest dose of sodium trifluoroacetate were noted including a cloudy swelling of the hepatocytes dose (2000 mg/kg) vacuolization

with sodium trifluoroacetate

of the hepatocytes

even after multiple

changes

of any of the

(1000 mg/kg) histological changes in the liver with a slight fat accumulation. At the higher

was detected

doses no hepatic 457

in hearts or kidneys

and

at all time periods (Rosenberg necrosis

was detected.

and Wahl-

BIOLOGICAL ANDHEALTHEFFECTS Mutagenicity TFA has been tested for mutagenicity of Salmonella

typhimurium,

was incubated indication

assay using two histidine-dependent

TA98 and TA 100 (Baden et al., 1976). TFA (150 mg/plate,

in an agar-overlay

of mutagenicity

in the Ames bacterial

assay at 37°C for 2 days without

was obtained

under conditions

TA98,

TA 100, and TA1535

at all concentrations

to note that while trichloroacetic

system.

No

of TFA was confirmed under similar was not mutagenic with Salmonella

used up to 35.7 mg/ml

in the presence or absence of polychlorinated biphenyl (Aroclor mitochondrial supernatants (Blake et al., 1981). The concentration mum non-toxic concentration for the bacteria. It is important

1.32 mmol/plate)

activating

where a positive control (N-methyl-N'-nitro-N-

nitrosoguanidine) was highly mutagenic. This lack of mutagenicity conditions (Waskell, 1978). In a third study sodium trifluoroacetate typhimurium

a microsomal

strains

(0.26 mmol/ml),

1254)-induced rat liver or testes post of TFA in these assays was the maxi-

acid has also been found to be nonmutagenic

in the

Ames assay (Rapson et al., 1980; Waskell, 1978), it is a hepatocarcinogen in mice (Herren-Freund, 1987). Trichloroacetic acid has been demonstrated to produce peroxisome proliferation in mice (DeAngelo et al.,

1986), which

1980), although on these reports insight

has been proposed

it is questionable the potential

into its potential

as one of the mechanisms

whether this mechanism

of hepatocarcinogenesis

applies in humans (Elcombe

of TFA to act as a peroxisome

proliferator

(Reddy

et al.,

et al., 1985). Based

should be investigated

to gain

as a hepatocarcinogen.

In Vitro Toxicology TFA at 4 mM (450 mg/l) reduced albumin to 56% and 85 % of controls,

the binding of the drugs warfarin and phenytoin to human serum respectively. TFA at 10 mM (1140 mg/1) correspondingly reduced

the binding to 44% and 77 % (Dale, 1986). The results suggest that TFA generally affects the conformation of the albumin. The potential of TFA to produce metabolic disturbances was tested in vitro in cultured Morris

rat hepatoma

7288C cells (Ishii and Corbascio,

1971). TFA (2.0 mM, 230 mg/l) did not

affect uridine or thymidine uptake, while at 10 mM (1140 mg/1) leucine and acetate uptake by the cells was not affected. Thus at these concentrations DNA, RNA, protein and lipid synthesis by the cells was not affected. When TFA was infused at 200 tamol/hr into 100 ml of perfusion liver the levels of lactate and pyruvate uptake and turnover inhibit

decreased

of lactate and pyruvate.

rather than accelerate

metabolic

medium

for an isolated

perfused

after 10 min (Stier et al., 1972). TFA produced

This result is unusual

in that fluorinated

compounds

rat

a higher usually

processes.

Antigenicity Aqueous solutions of chicken serum globin (10-15 mg/ml) and TFA (1.2 M) were mixed in a ratio of 1 to 1.5 at 4°C for 15 min. The mixture was dialyzed against water and lyophilized to produce a complex of TFA and chicken serum globin, which was used to immunize rabbits (Rosenberg and Wahlstrom, Undep these conditions TFA acted as a hapten and elicited antibodies. The clinical significance observation is unknown. 458

1973). of this

BIOLOGICAL ANDHEALTHEFFECTS

Analysis

Several

methods

is quantitated matographic

for the analysis

of TFA in biological

material.

In urine or serum TFA

by neutralizing with sodium hydroxide, esterifying with 2,2,2-trichloroethanol, and gas chroanalysis with a nickel-63 electron-capture detector (Witte et al., 1977). The detection limit

is 1 _g TFA/ml (Mario

are available

et al.,

body fluid. Another 1980). In serum

gas chromatography

method

uses isotachophoresis

TFA has been methylated

on Poropak

Q (Fraser

to quantitate

urinary

or blood TFA

and the head space vapor phase analyzed

and Kaminsky,

by

1987).

2. CONCLUSIONS Overall

there is sparse available

toxicologic

data on TFA. The acute lethality

of TFA in mice suggests

that it is only slightly toxic, and that its lethal effects at high doses are not dependent While a no adverse marrow

effect level has not been determined,

or small intestinal

effects,

25 mg TFA/kg

240 mg TFA/kg

produced

on its metabolism.

in rats produced

no body weight gains, relative

no bone

testis weight

gains, or testicular histologic changes in rats, and 2000 mg/kg every second day for 14 days in mice produced no hepatic

necrosis,

or heart and kidney

histological

changes.

TFA at 2000 mg/kg in mice significantly decreased hepatic but after 24-hr both levels returned to normal. Administration rats decreased

the hepatic

glycogen

content by 24 %, the percent

NADPH and reduced glutathione levels, of 150 mg TFA/kg/day for 5-6 days to liver/body

weight by 43 %, hepatic pyru-

vate kinase activity by 42 %, and increased hepatic glycerol 1-phosphate oxidase activity the lowest dose at which effects have been reported is 150 mg/day for 5-6 days. TFA is not mutagenic,

but no carcinogenicity

data is available.

However,

trichloroacetic

by 125 %. Thus

acid is hepatocar-

cinogenic in mice, although it is also not mutagenic in the Ames assay. While no chronic toxicity data on TFA is available it appears likely that on the basis of its resistance to metabolism, rapid clearance, lack of mutagenic potential, and low acute toxicity TFA is unlikely to exhibit significant chronic toxic effects. For a more complete assessment of TFA toxicity chronic studies are required, as well as acute studies in species other than the mouse. be investigated,

to gain insight

A German Senate Commission

The potential

for TFA to act as a peroxisome

into its hepatocarcinogenic for the Evaluation

of Health Hazards

mended that a blood TFA level of 2.5 _g/ml is risk-free assessment

has no experimental

or epidemiologic

basis.

459

proliferator

should

potential.

(Dallmeier

in the Work Environment and Henschler,

has recom-

1981). However,

the

N92-15451

ASSESSMENT OF DEGRADATION

OF EFFECTS

PRODUCTS

D.C. McCune

ON VEGETATION

FROM ALTERNATIVE

FLUOROCARBONS

and L.H. Weinstein

Boyce Thompson Institute for Plant Research Ithaca, New York

PRECEDING

PAGE

DL/_._'_K NOT

RLMED

BIOLOGICAL AND HEALTH EFFECTS EXECUTIVE If one

assumes

that the

mass

of fluorine

SUMMARY

(F)

deposited

under

an upper limit of 1.5x109 per year and all F returns as hydrogen into global rainfall and is deposited tation

would be about

by wet deposition,

steady-state

conditions

will have

fluoride (HF) that is uniformly

an upper limit for the concentration

dispersed

of F in precipi-

3 gg per liter (3 ppb).

This quantity of F, with reference to concentration or rate of deposition, is well below that heretofore considered to be of significance with respect to the direct effects on plants of air-borne F from industrial operations.

It also represents

(3 to 10 ppb). Moreover, tially no capacity cipally

a 30 to 100% increase

F at this concentration

to modify the chemical

determined

in what would be estimated

would be passively

speciation

of elements

by Ca or A1, and pH and concentration

the potential

of these elements

lower range

of pH should be sufficient

The wet deposition

to alter the activity

transported

of sulfate

F derived

of 3 ppb HF in rain and a total precipitation

as a complex

in rain. The activity

background with essen-

of F in rain is prin-

ions in precipitation

could affect

A1 concentrations

in rain at the

of F. Nevertheless,

to complex

to be natural

from the degradation

of fluorocarbons.

of 1000 mm per year would constitute

a negligible enrichment of the soil in terms of its normal contents or in comparison to that from perhaps the lowest detectable atmospheric concentration of gaseous F. Nor would this deposition of HF affect the chemistry

of acidic soils, and rain with a concentration

to affect the chemistry

of alkaline

some species

available

acetic acid, the effects cannot be estimated

on the effects or degradation

of plants can synthesize

Despite the great monofluoroacetate

would be needed

soils.

If one assumes that any or all F returns as a fluorinated no data are presently

of HF at least 103 greater

monofluoroacetate

of trifluoroacetic

acid in plants.

and omega-fluorooleate

because

Nevertheless,

and -fluoropalmitate.

chemical stability of the methylene carbon-fluorine bond, plants can metabolize and enzymes capable of degrading it occur in soil microorganisms. This leads to the

question of the ultimate

fate of trifluoroacetic

cal dehalogenation

and what end products

It is recommended

that research

acid with reference

to the possible

mechanisms

for biologi-

could occur.

be directed

to: (1) metabolism

of trifluoro-

and other halidoacetates

by

plants and microorganisms; (2) phytotoxicity of perchloroacetate and alkylhydroperoxides; (3) bioaccumulation and toxicology of these compounds in components of terrestrial and aquatic ecosystems; (4) further quantitative

knowledge

of the biogeochemistry

of F in natural

systems.

463 PRECEDING

P_GE

BL:_.!'_K NOT

FZL_,_ED

BIOLOGICAL AND HEALTH EFFECTS 1. ASSUMPTIONS The interaction of the degradation

products of fluorocarbons

by direct effects on the plant; by changes ate environment

of the plant.

mediated

For an assessment

to the nature of the environmental with the following boundaries.

exposures

with vegetation could occur in several modes:

by the plant; or indirectly, of any of these,

certain

that could be expected.

by an affect on the immediassumptions

are 0ecessary

as

Ours will be based upon an envelope

Firstly, we shall assume that the mass of fluorine deposited globally per annum under steady-state conditions will have upper and lower limits of 1.5x109 and 0.5x109 kg, respectively. These values are based on another assumption that upper and lower annual rates for global emissions of fluorocarbons are, respectively, 3x 109 and 1x l09 kg with fluorine constituting an average of 50% of the mass of the fluorocarbons. Secondly,

we shall assume that all fluorine

nated acetic acid. A subsidiary

assumption

(F) returns

either as hydrogen

currence of difluoromonochloroand monofluorodichloro-forms fluorine among them could be considered. Thirdly,

we shall assume

precipitation.

Concomitant

that fluorine assumptions

of 4.9x10 iv liters per year (Erchel, of fluorine

in precipitation

2. INORGANIC Concern (mainly

fluoride

(HF) or as a fluori-

is that the latter occurs as the trifluoro-form

is deposited

are that this is uniformly

dispersed

the oc-

and the partitioning

by the mode of wet deposition,

1975). Consequently,

would be, respectively,

are possibilities

although

of

i.e., by rainout

into an average

in

global rainfall

upper and lower limits for the concentration

3 and 1 /ag per liter (3 and 1 ppb).

FLUORINE

with the effects

with reference

of fluorides

on plants has been devoted

to gaseous HF and secondarily

tation as rain or mist and the presence

with paniculate

to that resulting forms).

of dew or free water on the foliage

from dry deposition

The occurrence

of precipi-

has mainly been considered

with respect to their effects on the accumulation of air-borne fluoride and not with fluoride in wet deposition. That is, precipitation has been viewed primarily with respect to its facilitation of the solution and subsequent absorption of deposits by the foliar tissues or its elution of deposited fluoride from foliage. (For example: the effects of mist on toxicity of HF and cryolite, McCune et al, 1977; models for the accumulation

of fluoride

by forage,

Craggs

and Davison,

1985).

Accordingly, our evaluation of inorganic fluoride from fluorocarbon degradation rests upon a comparison with what is known about the effects of industrial emissions and what could be considered the natural condition.

2.1.

HF in precipitation

One problem anthropogenic

is to what extent the concentration sources,

bons represent to the conclusion

of fluoride in rain can be partitioned

and then to what extent the products

an increased

burden

that the assumed

from the atmospheric

degradation

over that contributed

by the other sources.

quantities

in rain due to the degradation

of fluoride 464

into natural

In general,

and

of fluorocarone can come

of fluorocarbons

BIOLOGICAL ANDHEALTHEFFECTS may represent

close to the detectable

no effect on the chemistry

2.1.1.

of present

levels,

be deposited

as complexes,

and have

Quantity

In a metropolitan frequently

area (Yonkers,

were greater

considered enriched

increment

of rain water or on the plant.

New York),

than 50 ppb in rainfall

free of anthropogenic

influence

by a source (probably

fluoride

had fluoride

by washout)

concentrations

(Jacobson

et al.,

never exceeded

100 ppb and in-

1976). In Newfoundland,

rain and snow

averaging

had average

less than 10 ppb whereas

concentration

precipitation

of 280 ppb in rain (range

of 110

to 580 ppb) and an average of 360 ppb in snow water (range of 110 to 1040 ppb) (Sidhu, 1982). Barnard and Nordstrom (1982) found a difference between coastal and inland sites in the distribution of values. Coastal

values

ranged

concentrations;

inland values

from mass balance rather

from 2 to 24 ppb with a median of 4.2 ppb and were uncorrelated

than from maritime

2.1.2.

ported

as a complex

water.

Basically,

aerosols,

volcanic

has concluded

activity

of 9.4 ppb. They further

in precipitation

concluded,

was anthropogenic

(2 to 3 ppb), or soil particles

in origin

(ca 1 ppb).

ions determining

upon the pH. Above

in dust determine,

the activity

speciation

of elements

in rain

in addition

to quantity,

the ac-

pH 5.0, the solubility

of fluoride

than 4 by the formation

The solution of sulfate ions in precipitation to alter the activity of fluoride.

Nevertheless,

of fluorocarbons

will secondarily

would be Ca

of AI(III) regulate

limit its

nearly all fluoride

of AI-F complexes. affect Ca and AI and thereby

at the concentrations

would not alter the acidity

in solution

of Ca and other salts of fluoride

than 10 -4 M. Below pH 4.5, hydrates

of AI:F of greater

the degradation

to modify the chemical

and form of minerals

that the major

to a level no greater ratios

no capacity

present in rainfall, fluoride is passively trans-

in rain.

Ares also concluded or A1, depending

that at the concentrations

with essentially

the composition

tivity of fluoride

at molar

that most of the fluoride

Chemistry

Ares (unpublished)

activity

ranged up to 34 ppb with a median

considerations,

with sodium

of fluoride assumed,

or composition

their potential

HF derived

from

of rain.

That AI concentrations in rain should be sufficient to complex fluoride at the lower pH range is deduced from limited data. In the vicinity of GiSttingen, levels of A1 ranged from 48 to 174 ppb with a mean of 89 ppb (Ruppert, ranging

2.2.

from

1975). In the vicinity of Soiling,

10 to 1720 with a median

found concentrations

of A1 in rain

Effects on soil

The fluoride

content

of normal

soils ranges

depth in the soil, and content of organic son,

Ares (unpublished)

of 100 ppb.

1983). Assuming

a concentration

about 30 gF ha -1 would be deposited

matter,

from 20 to 1000 ppm depending with an average

465

present,

of about 200 ppm (see review by Davi-

of 3 ppb in rain and a total precipitation per year, which

upon minerals

is equivalent

of 1000 mm per year,

to an enrichment

of about 0.04 ppm

BIOLOGICAL ANDHEALTHEFFECTS (using Davison's

bulk density factor for soil). By comparison

and using Davison's

estimate

of deposition

velocity, exposure to air averaging 0.05/agF m -3 would result in the deposition of about 380 gF ha -t per year. Consequently, this wet deposition would constitute a negligible contribution to the soil in terms of normal contents or in comparison of gaseous fluoride.

to that from perhaps

the lowest detectable

atmospheric

concentration

The data of Ares (1986) would also indicate that wet deposition of HF in the assumed range of concentrations would not affect the soil solution in acidic forest soils. In these, it was estimated that 99.9% of fluoride was complexed with A1, and one could conclude that 3 ppb in rain would not affect the chemistry of the soil. Ares postulated that the solubility of fluoride in alkaline soils (pH 7.2 to 8.2) is controlled by ralstonite (NaMgAIF6) at high Na levels or fluorite (CaF2) at low Na levels and that rain with a concentration at least 103 greater than that assumed In areas subject to airborne soil chemistry

fluoride

have been observed

in this assessment

from industrial

would be needed to affect the soil chemistry.

emissions,

enrichment

of fluoride

(Ares, 1978; Fiuhler et al., 1982; Polomski

and changes

et al., 1982; Sidhu,

in

1982).

Nevertheless, it has been concluded that the increased levels of fluoride found in foliage in these areas represents more the result of increased deposition directly to the plant than of uptake from an increased level of fluoride in soil (Braen and Weinstein, 1985; McClenahen, 1976).

2.3.

Gaseous

HF

By way of comparison, the effects of gaseous fluoride are relatively well known although knowledge is not as plentiful as would be desired for practical applications to environmental quality. Table 1 lists some values for different averaging times of what could be considered protective for three classes of vegetation. Some standards for fluoride are also based on the concentration present in foliar tissue, and Table 2 presents a example of this kind of standard. The short-term or young foliage

(24-hour) value for highly sensitive plants is based upon the effects of HF on gladiolus of conifers, such as spruce, fir, and pine (see reviews by McCune, 1969; Weinstein,

1977). The l-month

Table

value for highly sensitive

plants represents

1. Possible acceptable limits for atmospheric with reference to effects on vegetation.

Plant

Low

concentrations

24 hours 1.6

466

for grapevines

of gaseous

Concentration

Sensitivity class High Moderate

what could be protective

_gF

fluoride

m-3)

Averaging time 1 month 7 months 0.4

0.25

3.6

1.5

0.6

10.0

2.5

1.2

BIOLOGICAL ANDHEALTHEFFECTS Table 2.

Standards

of the State

of Maryland

for the concentration

of fluoride

in

vegetation.

Concentration

Class of vegetation

of fluoride

(_gF per g dry mass) Forage

60 b

80 350

for cattle a

Field crops plants

400

Conifers & evergreens (current) .... (older) Deciduous trees & shrubs

500 1O0d

Grasses

1500

Ornamental

a) Unwashed

& herbs

35 c

75 d

(not grazed)

samples

b) Mean for two months c) Mean for 12 months d) Foliage

washed

before

analysis

based on the work of Doley

(1986) with the Chardonnay

cultivar

of Vitis vinifera.

The 7-month

concen-

tration for highly sensitive plants is based in part on the results of MacLean et al. (1984) as related to the occurrence of suture red spot (SRS) on fruit of peach. This is one of the most sensitive responses of plants to HF and also an economically is not of concern, The averaging to furnish

a higher periods

the experimental

significant

effect.

If protection

against

value such as 0.4 _gF m -3 based upon Doley

above were chosen data, However,

mainly because

they represent

they should also recognize

the occurrence

(1986)

could

the exposure

of SRS

be used. regimes

what characteristics

used

of exposure

could be operationally significant in the vicinities of the sources and receptors. Given the variability observed in the concentrations of HF in quotidian or weekly cycles and the temporal variations in the susceptibility of plants under ambient than 24 hours

conditions,

and less than 30 days.

whether a mean value is appropriate ived could be zero. In general one could conclude tive for vegetation wet deposition

3. HYDROGEN Although natives,

one could propose

With respect

periods

to a seven-month

shorter

value,

when the median of the population

that atmospheric

would result in greater

of HF from fluorocarbon

of fluoride

or greater

there is some question

of samples

levels of gaseous fluoride

accumulations

than 24 hours from which

below those considered

in foliage

as to

it is der-

protec-

and soil than would the

degradation.

CHLORIDE

hydrogen

chloride

could also result from degradation

it is much less toxic to plants than fluoride.

For example, 467

of some compounds Guderian

proposed

(1977) recommends

as altera concen-

BIOLOGICAL ANDHEALTHEFFECTS trations

no greater

concentrations

than 50 _g m -3 as being

of chloride

protective

in foliage associated

of the most sensitive

with thresholds

vegetation.

In addition,

for foliar injury are in the range of 0.2

to 2% by dry weight.

4. FLUORO-ORGANIC

COMPOUNDS

No data are presently

available

do synthesize monofluoroacetate and microbes.

of the effect of trifluoroacetic

acid on plants. Nevertheless,

and some data is available on the degradation

some plants

of this compound

by plants

The distribution of fluorine-containing organic molecules in nature appears to be limited to its occurrence as monofluoroacetate (Marais, 1944) and in omega-fluorine homologues, fluorooleate and fluoropalmitate (Peters (1972).

et al. 1960; Ward et al.,

The carbon-fluorine

accomplished

by refluxing

acid. Complete at 400C.

release

Monofluoroacetate thesis"

1964). For more details on their distribution

bond in these compounds in 20 percent

occurs

only after refluxing

is a naturally-occurring

in many mammals

which blocks aconitic

(Peters,

hydratase

or heating

in 30 percent

compound

stability

sodium hydroxide

is

sulfuric

or by sodium fusion

of monofluorocitrate

and can result in death. It seemed

et al.

and its slow release

at 100C in concentrated

in plants, and has been implicated

1952), i.e., the biosynthesis

stability of the methylene carbon-fluorine of the carbon-fluorine from a pseudomonad

has extraordinary

sodium hydroxide

see Weinstein

in "lethal

syn-

from fluoroacetate,

likely that, despite

the great chemical

bond, there might be enzymes capable of degrading

it. The cleavage

bond of monofluoroacetate was first reported by Horiuchi (1962) using extracts isolated from soil. Although defluorination occurred, significant defluorination was

not reported until Goldman (1965) isolated a pseudomonad from soil that grew on a medium containing monofluoroacetate as the sole carbon source. The results were quickly verified for other soil organisms (Tonomura

et al., 1965; Kelly,

haloacetate halidohydrolase lyzes the reaction

1965). The enzyme

(Goldman

and Milne,

XCH2COO" where

capable

of cleaving

1966; Goldman

+ OH" _

the carbon-fluorine

et al., 1968; Goldman,

bond was a

1969)that

cata-

X' + HOCH2COO"

X = F, CI, or I.

Preuss et al. (1968,

1969) first reported

that higher

plants can cleave

the methylene

carbon-fluorine

bond. This was shown by the liberation of t4CO2 following incubation with 2-_4C-fluoroacetate in germinating seeds of peanut, castor bean, and Acacia georginae. Pinto bean seeds were not able to liberate L4COE. In peanut, inorganic fluoride was one product of the reaction. The other was postulated acid. The enzyme that accomplishes defluorination in plants has not been characterized. The facility by which the carbon-fluorine isms and higher plants, one of the major probable

leads to the question

products

that plant and/or

of photochemical microbial

bond can be cleaved of the ultimate oxidation

enzymes can remove 468

by enzymes

to be glycolic

found in soil microorgan-

fate of trifluoroacetic

of several of the alternative

acid (Pattison,

1959),

fluorocarbons.

fluorine atoms from the molecule.

Whether

It is de-

BIOLOGICAL ANDHEALTHEFFECTS halogenation

will occur as it does with dichloroacetate

gen atoms together, product,

or whether

(Goldman

it might be a stepwise

et al., 1968), i.e., removal

dehalogenation,

with monohalidoacetate

of both haloas the end

is not known.

5. RECOMMENDATIONS It is apparent heretofore

that the quantities

considered

of inorganic

fluoride

assumed

in this discussion

to be of interest with respect to the environmental

are well below those

consequences

of industrial

opera-

tions. They could represent a doubling of what would be estimated to be natural background. ly, research on their possible biogeochemical effects should be directed to the identification

Accordingof natural

systems presently uninfluenced by anthropogenic and transformation for fluoride in them.

of transport

With reference to: (1) metabolism

to the effects of trifluoro-

of fluoro-organic

fluoride and a better understanding

compounds,

and other halidoacetates

tion and toxicology of these compounds in components of perchloroacetate and alkylhydroperoxides.

it is recommended

of pathways

that research be directed

by plants and microorganisms;

of terrestrial and aquatic ecosystems;

469

(2) bioaccumula(3) phytotoxicity

Annex

A

Experts

and Reviewers

PRECEDING

PI-_GE BL_.P,_K NOT

FILMED

ANNEX EXPERTS AND

A

REVIEWERS

INVOLVED

IN AFEAS

EXPERTS R. Atkinson

University

W.L. Chameides P.S. Connell

Georgia Institute of Technology Lawrence Livermore National Laboratory

R.A. Cox

Harwell

R.G. Derwent D.L. Filkin

Harwell Laboratory E. 1. du Pont de Nemours

& Co., Inc,

D.A.

E. 1. du Pont de Nemours

& Co., Inc.

Drexel University E. 1. du Pont de Nemours

& Co., Inc.

J.P. C.H.

Fisher Friend Hales

R.F. Hampson I.S.A. Isaksen L.S. Kaminsky M.K.W. Ko

of California,

Laboratory

National

Institute

Oslo University State University Atmospheric

Institute

D.C.

McCune

M.O.

McLinden

Boyce Thompson National Institute

University

and Technology,

and Environmental

National

H. Niki M.J. Prather

of Standards

Gaithersburg

of New York at Albany

M.J. Kurylo R. Lesclaux

M.J. Molina

Riverside

of Standards

Research,

Inc

and Technology,

Gaithersburg

of Bordeaux Institute for Plant Research, Ithaca of Standards and Technology, Boulder

Jet Propulsion Laboratory York University, Ontario NASA

Goddard

Institute

for Space Studies

V, Ramaswamy S.P. Sander

Princeton

F. Stordal

Oslo University

N.D.

Atmospheric Kfa Julich

and Environmental

Research,

Inc.

W-C Wang L.H. Weinstein

Atmospheric

and Environmental

Research,

Inc,

P.H. Wine D.J. Wuebbles

Georgia Institute of Technology Lawrence Livermore National Laboratory

R. Zellner

University

Sze

A. Volz-Thomas

University

Jet Propulsion

Boyce

Laboratory

Thompson

Institute

for Plant Research,

Ithaca

of Hannover

REVIEWERS D.L.

Albritton

National

Oceanic

J.G.

Anderson

Harvard

University

R.E.

Banks

J.J. Bufalini

University of Manchester Institute of Science US Environmental Protection Agency

A.W,

Davison

Newcastle

W.B. D.D.

DeMore Des Marteau

Jet Propulsion Clemson

and Atmospheric

University Laboratory

University

R.A. Duce

University

of Rhode Island

A. Goldman

University

of Denver A-1

Administration and Technology

EXPERTS M.R. Hoffman C.J. Howard N. Ishikawa J.L. Moyers V. Ramanathan A.R. F.S.

Ravishankara Rowland

AND

REVIEWERS

California

Institute

INVOLVED

National University

(Continued)

of Technology

National Oceanic and Atmospheric F&F Research Centre, Tokyo National Science Foundation University

IN AFEAS

Administration

of Chicago Oceanic

and Atmospheric

of California,

Administration

Irvine

P. Simon

Institut d'Aeronomie

H.O. Spauschus S. Solomon

Georgia Institute of Technology National Oceanic and Atmospheric

Administration

A. Tuck

National

Oceanic

Administration

R.T.

National Harvard

Aeronautics University

Watson

S. Wofsy

Spatiale

de Belgique

and Atmospheric

and Space Administration

A-2

Annex

B

Companies

Sponsoring

AFEAS

ANNEX COMPANIES

B

SPONSORING

AFEAS

Akzo Chemicals

Netherlands

Allied-Signal Asahi Glass Atochem

USA

Chemical

Corporation Co., Ltd.

Industries

of Northern

Daikin Industries, Ltd, E. I. du Pont de Nemours Hoechst

Japan France Greece,

Greece

S.A.

Japan USA

& Co., Inc.

Germany UK

AG

ICI Chemicals and Polymers ISC Chemicals Kali-Chemie AG LaRoche

Ltd.

UK Germany USA

Chemicals

Montefluos SpA Pennwalt Corporation

Italy USA

Racon

USA

(Atochem)

B-1

Annex

C

Statement

of Work

PRE.CEDING

PI'I.GEBLh._',_K NOT

FILMED

ANNEX C STATEMENT

Each reviewer the following. possible

should prepare

The reviews

and fifty copies

The reviews 1. Is there

of the reviews

3. Are the findings

supported

reported

of each paper of the AFEAS

should be brought

the following

information

2. Are the conclusions

review

should be sent to the chairman

should address significant

a one page written

OF WORK

specified science

to the AFEAS

with their name

committee

conference.

questions:

relevant

to the subject

by the information

in the executive

summary

that is not included

in the review

presented

in the review

supported

by the information

paper?

paper? in the body of the

paper? Are all of the important points covered in the executive summary? Does the summary vide the correct level of detail or is information included that should be removed? I. Physical and Chemical Properties: Since model calculations and evaluations information to submit A.

developed

in these reviews

their review

Solubility

Based on information

of potential

biological

as input, Experts

Vapor

Pressure,

in the literature,

Hydrolysis

supplied

pro-

and health effects will require the

answering

papers by not later than 28 February,

in Water,

in

as early as

these questions

will be required

1989.

Rates

by AFEAS

member

companies

and available

from

other sources, what are the recommended temperature dependent values of the solubility in pure water, solubility in sea water, vapor pressure, and hydrolysis rates for each of the HCFCs and HFCs? Expert - Mark McLinden Reviewer B.

- H.O.

Reaction

Spauschus

Rate Constants

Based on available for reaction

information,

on these rate constants? Reviewers C.

D.

- Bob Hampson,

temperature

dependent

rate constant

and O(_D)? What are the error limits

Mike Kurylo

and Stan Sander working

together.

and A. R. Ravishankara

information,

in the 8 - 13 m range)

limits on these cross-sections?

Reviewers

and HFCs with hydroxyl

Cross-Sections

Based on available error

Experts

- W. B. DeMore

Absorption

(primarily

what is the recommended

of each of the HCFCs

what are the recommended cross-sections Expert

ultraviolet

(190-400

for each of the HCFCs

- Mario

nm) and infra-red

and HFCs?

What are the

Molina

- P. Simon and A. Goldman

Degradation

Mechanisms

Based on available

information,

how will the HCFCs C-1

and HFCs degrade

in the troposphere

after

the initial hydrogen

atom abstraction

what is the most likely atmospheric ble fluorine-containing the atmosphere? experts,

lifetime

intermediates

Roger

Reviewers

what are the intermediate

of each of these products?

would be formed?

As this is one of the more important

are being asked to address

together;

by hydroxyl,

Atkinson;

these questions.

Hiromi

- All reviewers

should compare

and

Is it likely that relatively

How would the products set of questions,

Experts

Niki; and Reinhardt

and final products be removed

four experts,

stafrom

or teams

- Tony Cox and R. Lesclaux

of

working

Zellner.

the papers to identify

inconsistencies

and determine

if

they are due to uncertainties that cannot be resolved without further research or if they are due to errors in one or more of the papers. Specific responsibilities for more extensive reviews

are:

J. G. Anderson J. Bufalini

- papers

- papers

W. B .DeMore

prepared

- papers

A.R. Ravishankara

prepared

by R. A. Cox and R. Lesclaux

by R. Atkinson

prepared

and R. Zellner

and H. Niki

by H. Niki and R. Zellner

- papers prepared

by R. Atkinson

and R. A. Cox and R. Lesclaux

Each of the following reviewers should prepare a single review of the group of four papers. The group should be reviewed for completeness and consistency. Causes of any inconsistencies should be discussed. Each of these reviewers

should suggest a single executive summary

based on the four executive summaries.

F. S. Rowland R. E. Banks N. Ishikawa II.

Uncertainties

in Atmospheric

Experts answering 1 April, A.

Lifetimes

these questions

will be required

to submit their review papers by not later than

1989.

Tropospheric

Hydroxyl

Based on measurements

Concentrations of the isotopic

ratio of carbon in atmospheric

carbon

monoxide,

what is

the average tropospheric hydroxyl radical concentration and what are the uncertainties in the derived concentration? Given that the rate constant of the reactions of HCFCs and HFCs with hydroxyl are temperature the HCFCs

dependent, what is your best estimate of lifetime (with uncertainty limits) of each of and HFCs? Experts - Andreas Volz-Thomas and R. G. Derwent working together.

Given the available

data base on methyl chloroform

centrations

and estimated

compounds

and how sensitive

global emissions), are the lifetime

and HCFC-22

what are the calculated to variations 12-2

(measured atmospheric

atmospheric lifetimes

in these data, e.g. latitudinal,

con-

of these seasonal,

vertical profile? Assuming

Calculate

that reaction

the effect of a reasonable

variation in each of these parameters

with OH is the only sink for methyl chloroform

and HCFC-22,

in turn.

how do un-

certainties in the data base for these compounds extrapolate to influence the derived OH concentration? Extend the sensitivity calculation from effect on lifetime to effect on *OH* and hence on the lifetimes

of alternative

(with uncertainty Are the inferred reaction e.g.

fluorocarbons.

limits) of each of the HCFCs lifetimes

what is your best estimate

hydrolysis

for methyl chloroform

of methyl chloroform?

- S. Wofsy

Individual

reviews

and HCFC-22

compared.

If there are inconsistencies

that cannot

Expert

should be prepared

be resolved

without

- Michael

for each paper the reviewer

further

of lifetime

and HFCs. consistent

with OH is the only sink? Is it possible that there is another

Reviewer

B.

Based on this analysis,

research

with the assumption

that

sink for one or other compound,

Prather

and the conclusions

should determine

of the papers

should be

if they are due to uncertainties

or if one or both of the papers

contain

errors.

Hydrolysis Based on available

information

of methyl chloroform, of average

hydroxyl

on hydrolysis

HCFC-22 concentrations

derived

is being asked to determine

and HFCs

using measurements

the assumption that there are no other significant working

rates, what are the most likely atmospheric

and the other HCFCs atmospheric

if that is a valid assumption.)

against

hydrolysis?

of methyl chloroform

sinks of methyl chloroform. Experts

lifetimes (Estimates

are based on This question

- Paul Wine and Bill Chameides

together.

What are the atmospheric are the ultimate products working

lifetimes

of the compounds

that would be formed

identified

in solution?

in I.D.

against hydrolysis?

What

Experts - Paul Wine and Bill Chameides

together.

Reviewers

- M. R. Hoffmann

In addition

to preparing

potentially

important

and D. D. Des Marteau

reviews

of the papers the reviewers

liquid phase reactions

involving

should prepare

compounds

identified

brief summaries

of other

in I.D. and not addressed

by AFEAS. III. Natural

Sources

Experts answering 1 May,

these questions

will be required

to submit their review

paper by not later than

1989.

What are the source strengths and atmospheric concentrations of compounds containing chlorine and/or fluorine due to natural sources? What are natural concentrations of fluoride in ground water? What are the concentrations rivers,

of fluoride from natural sources in rain water and surface waters (oceans,

lakes)? What concentrations

are found in metropolitan

dation? What are the source strengths ic compounds Reviewers

in the atmosphere?

- J. L. Moyers

of other inorganic

Expert

- J. Friend

and R. A. Duce C-3

water supplies

compounds

before and after fluori-

that would be converted

to acid-

IV. ModelCalculations Expertsanswering thesequestions will berequiredto submittheirreviewpapersby notlaterthan 1 May, 1989. A. Stratospheric Ozone Giventheinformationsuppliedby theexpertsanswering I.B., I.C. andII., whatarethecalculated ozonedepletionpotentials (includinguncertainties) of theHCFCs?Basedonavailableinformation, couldHFCscontributeto ozonedepletion? Experts- DonFisher,IvarIsaksen,DakSzeandDon Wuebblesworkingtogether. Reviewers

- S. Solomon

B. Tropospheric

and A. F. Tuck

Ozone

Given the information

supplied by the experts answering

I.B., is it likely that the HFCs and HCFCs

would contribute to production of photochemical oxidants sis, how would emissions of HCFCs and HFCs (currently, kilograms

per year) compare

Reviewer

- J. Bufalini

C.

to natural

sources

in the vicinity of release? on a global baemissions of CFCs are about one billion

of ozone precursors?

Expert

- Hiromi

Niki.

Global Warming Given the information

bon global warming Don Fisher, Reviewer

potentials

by the experts (including

answering

uncertainty

Dak Sze, and one other climate

I.B., I.C. and II., what are the halocar-

limits) of the HCFCs

modeler,

working

and HFCs?

Experts

-

together.

- V. Ramanathan

V. Biological

and Health

Experts I May,

supplied

answering

Effects these questions

will be required

to submit their review papers by not later than

1989.

Based on the answers to these questions in sections I. and II., is it likely that the decomposition products from annual emissions of one billion kg. (an amount that is approximately equal to current emissions

of CFCs) could contribute

should range from humans lowing topics

to biological

or health effects?

all the way down to microorganisms.

for each of the classes

of degradation

1. Known acute and chronic affects to all concentrations, tions for which data are available. 2. Existence

of a dose-response

of data on quantitative

4. Biochemists

reaction

mechanisms,

dose-response if known. C-4

to be considered

The review should address

compounds

the fol-

on the list:

but with emphasis on the lowest concentra-

threshold.

3. Availability

The organisms

relationships.

5. Repair 6. Potential

mechanisms

7. Most important

Reviewer Individual

ability of the organism

effects at projected

parent compound

Experts

and/or

concentrations

of 1 billion kg/year research

- L. S. Kaminsky;

needed

to adapt.

corresponding

at steady

to resolve

uncertainties

and L. H. Weinstein

to hypothetical

emissions

for a given

state. relevant

to the above items.

and D. C McCune

working

together.

- A. Davison reviews

should be prepared

for each paper

and the conclusion

of the papers

should be

compared. If there are inconsistencies the reviewer should determine if they are due to uncertainties that cannot be resolved without further research or if one or both of the papers contain errors.

C-5

ili!i!i_

'

i!iii!i!iiii:_ii i

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