2o735o - NTRS - NASA

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PO43, 40 pptv. Na ÷, 25 pptv. NH4+,. 17 pptv K÷, 6 pptv Mg 2÷, and 14 pptv Ca 2+. Analytical details for other species discussed in this paper are provided.
JOURNAL

OF GEOPHYSICAL

RESEARCH,

VOL.

101, NO.

D1, PAGES

177%1792,

JANUARY

20, 1996

2o735o Asian influence over the western North Pacific during season: Inferences from lead 210, soluble ionic species ozone J. E. Dibb, J. D.

_ R.

W.

Bradshaw,

Abstract.

Talbot,

4 and

Aerosol

_ K.

S. T.

samples

Tropospheric Experiment October 1991) revealed

I. Klemm,

Sandholm

_ G.

L. Gregory,

closely

collected

that

of 03 and

over

the

of 21°pb, while

7Be.

soluble aerosol-associated convection over the Asian

western

Free

have

boundary

It is well established a number [e.g.,

insoluble

precursors),

layer

the

into

that Asian

free

air transported

causes peak concentrations

of remote

Prospero

Pacific

et al.,

hence

escape

troposphere

by

island

1985;

sites,

Merrill

eastward

of mineral especially

et al.,

in Asia may play an increasing

of the atmosphere of

the

over the western

Pacific

sampling

Exploratory

campaign

1989;

in the

aerosols

in the spring Gao

Pacific.

(PEM-West

- October

period

stronger.

mission,

in February

when the continental

Analyses

of results

from

influence PEM-West

and will be reported in later papers. This paper discusses the composition collected 4"

soluble

during PEM-West ionic

species

SO4 =, MSA,

aerosol PO4

to the distributions

Aerosol samples were collected on Zefluor

filters.

in parallel,

samples

and references therein]. We distribution of 2_°pb and its

of other

aerosol-associated

of continentally

and

influenced

air over

Two sampling

were

constant

altitude.

exposure

periods

Na*,

for radionuclide and soluble ionic analyses separate 90-ram-diameter, 2-1am pore size, systems

so that exposure

samples

identical. During

times

Sampling

was

the intensive

generally

(see below)

were operated

for the radionuclide

between

restricted flights

and ionic

to flight

this resulted

20 and 45 min

legs at in filter

in duration.

On transit flights with long constant altitude legs, aerosol filters were changed at 45- to 60-min intervals. The volume of sampled

tlnstitute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham. 2Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virgina. 3NASA Ames Research Center, Moffet Field, California. 4Georgia Institute of Technology, Atlanta.

air thus ranged collected

1.4 - 17.5 m 3 STP.

on each

of the 17 flights

Two during

to eight PEM-West

samples

were

A.

Collecting aerosol samples without altering the characteristics of the ambient aerosol population is never a trivial problem; high-speed

Copyright 1996 by the American Geophysical

radionuclides 2'°Pb and 7Be have well-defined

Sampling

the to be

3",

activity.

Methods

of a suite of waterC204-,

are

vertical

the utility of 2t°pb as a tracer the Pacific.

B are in progress of

A. Concentrations

(CI-, NOr,

was expected

during

this issue; Gregory et al., this issue; Smyth et al., this issue; Talbot et al., this issue]; these independent approaches validate

B, was flown

1994 to characterize

free

atmosphere. Several companion papers address this same question with additional tracers and meteorological analyses [Browell et al.,

airborne

1991 was to charac-

PEM-West

- March

in

wet of the

gaseous species measured during PEM-West A, in order to assess the influence of Asian air on the composition of the Pacific

chemistry instrumentation, flew 17 missions, totaling 120 hours, over the Pacific Ocean toward this end (see overview by Hoell et The follow-up

depleted

A flights. species that

convective

relationship

be near the low point in its seasonal cycle. The NASA Ames DC8, with an extensive load of remote and in situ atmospheric

spring

was

respectively [see Dibb et al., 1992, focus on the spatial and altitudinal

et al.,

The objective A)

[ (135)

(18)

(17)

(t.2) 10 km

All

Other

Fits

200 t t /

150

I / / t t I

100

/ / / 1

5O

% --

0

'

'

'

'

0

J

_

-'

-'

y '

1000

= I

27 '

'

+

0.031043X ' I w

'

2000

,

R= , I

,

3000

0.79189 ' ' '

4000

-'

7-

--

--

y

=

42.478

÷

-0.042806x

R=

0.44634

I

5000

10

8O

1000

2000

3000

4000

5000

km

1

6O

C3 ¢3t.

o 20

_0

-0

--

....

-_

y

=

36.489

,

i

'

f

0

÷

'

'

'

0.014118x '

_

400

'

R= I

'

O•



0.63247

....

_

800

'

I

i

i

J

i

i

J

1200

i

i

i

J

i

_

400

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r

_

]

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O •

--

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=

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÷

0.049567x

'400' 7Be (fCi m "3 STP)

R=

'6()0'

0.70397

'8(_0

'

'

'200'

'4(30'

'600'

7Be (fCi m "3 STP)

Figure 4. Scatterplots of 03 against 7Be in the free troposphere. The three transit flights (4, 5, and 21) were flown between California and Alaska, Alaska and Japan, and from Hawaii to California. All remaining flights over the western Pacific are compared to these three.

'

I

8OO

DIBB

600

Fits

ET AL.: ASIAN

INFLUENCE

OVER

WESTERN

NORTH

Scatterplots

6 - 13

tude/region

PACIFIC

of atmospheric

bin reinforce

1787

nitrate

versus

the impression

relationships exist in the PEM-West nitrate and 2t°pb concentrations only layer over the remote

go

400

turn

western

decay to 2_°pb occurs

NO x (from

the boundary

Pacific more

layer

2_°Pb for each

that no consistent A data covaried

(Figure

quickly

lati-

strong

set. Atmospheric in the boundary

7). It is possible

that

than the conversion

or lightning)

to nitrate,

of

but similar

plots of NOx and NO r against 2'°pb (not shown) also indicate little or no correspondence. However, PAN concentrations tended to 200

covary

with those of 2_°Pb at all altitudes

near Asia and in the 7-

to 8.5-km bin over the remote western Pacific (Figure 8). The observed correlation between n°Pb and PAN, alone of the tn Q.

o_ Z

o

_°°_86°'11°





reactive N species, may be consistent with wet convection of NO X and tuRn from the continental boundary layer resulting in strong



2t°Pb-NO3-

150

relationships

in remote

size that the modified

+

boundary

oceanic layer

regions.

We hypothe-

air that passed

through the

o_

deep wet convection

Z "1-

tions that favored the formation of PAN over inorganic forms nitrate. As middle to upper tropospheric air over Asia enriched

100

21°pb (and/or somewhere generate •

5O

oo

NO3

tuRn)

Fits

14 - 19

HNO3,

5

10

15

20

25

21°pb (fCi m 3 STP)

source

This

A data set allows

a preliminary

assessment

technique

used at the remote

island

Older

sampled

air, presumably

Asian continent, between

air

sites is

21°pb and atmospheric

Older

during

Continental

The

little or no relationship

with 2_°pb when

5). It may be that the previously

(Figure

stratification

of the

free

troposphere

obscuring any relationships The vertical distribution western

Pacific

species

in Figure

are enhanced

6. Near

to those

Asia,

in the boundary

of all measured

all of the N species layer relative

team.

below

N western in the

over

the

A data

archive).

N

Hawaii

caused

reactive except

at low levels

region

Pacific, modest boundary layer

PAN

Trajectories had circled

indicated

at the maximum Hawaii

Loa

the DC-8

flyby

was

conducted

by

was restricted

were easterly

enare

to

and back

ridge

from near the North

of high

and relatively sampling

light

altitudes

pressure

over

winds

aloft.

indicate

curvature

that air

for the previous

5

- 7 days. None of these trajectories ventured more than 10 ° away from Hawaii, so it is unclear whether any continentally influenced air in the free troposphere Lead

originated

210 concentrations long-range

transport

above

over Asia or North America. the boundary

toward

layer ranged

the surface

of continental

(Figure

much

relative

to the majority

spondence

stratospheric

younger

ratios

were

nearly

continental

outflow

higher

I and 9) appear

lower

near Asia

of PEM-West the input

high-level

than those

(compare

7Be concentrations

to reflect

air during

fivefold

N species that PAN observed

Figures

at 5 km over

A flights of upper

transport,

3 -

9), indi-

air in the free tropo-

sphere. In this case the altitude profiles of all reactive were quite similar to that of 2_°pb. It should be noted

9). The

to be weak.

transport

with anticyclonic

ly large enhancements of NO x and NOy near 8.5 km over the remote western Pacific correspond to proportionally smaller increases in 2_°Pb and PAN concentrations. Overall, the correappears

20

measurements

level winds

subsidence

mixing

2_°Pb and NO 3 or HNOj

for this hypothesis.

Mauna

A midtroposphere weak

accompanied by slightly elevated NO 3 concentrations, but concentrations of the other N species are quite low (Figure 6b). Relative-

between

Loa 1995;

American west coast (all meteorological analyses were provided by the GTE project office and are available from the PEM-West

to the free-tropo-

in this

et al.,

trajectories

cating

reactive

from the

relationships

20, the Mauna

Flight

the from

5 km. Surface

[e.g.,

of

Study,

Sampling

be

source

Flight

A [see Atlas

with ground-based

8 fCi m 3 STP and decreased

1993]. Over the remote of 2t°pb concentrations

farther

tighter

some support

of

are may

important

to shower

nitrate.

objective

the highest-altitude bin near Asia, where 2_°Pb concentrations the lowest of the entire profile. High-altitude aircraft traffic an

et al., this issue].

A is

spheric air just above (Figure 6a), but we do not consider that the n°Pb enhancement in the boundary layer is related to wet convection (see above). Aerosol NO3, NO x, and NOy also increase in

Kasibhatla, hancement

Pacific

noted

PEM-West

that are present. of 2t°pb in the two regions

is compared

altitudes

results from all altitudes during

of most NOx

western

[Talbot

PEM-West

Air Case

primary

the MLOPEX

data show

are considered

the

more prevalent

might be expected

conducted

NO3and

nitrate

over

as little as 2 days previously

intercomparison

A atmospheric

to

in both 2_°pb

A. Trajectory analyses indicate that the contiencountered by the DC-8 had generally been

continental

felt to efficiently collect HNO3 in addition to aerosol NO 3 [Savoie et al., 1989]. If atmospheric nitrate is considered to be the sum of HNO3, the PEM-West

NO x may then be converted

of

these hypotheses. The filter sampling

of PAN will

et al., 1987; Singh

is the initial product

Hoell et al., this issue] provides PEM-West

[Singh

of in

and subsides

an air mass enriched

If PAN

free-tropospheric

during PEM-West nental air masses

flyby The

eastward

in propor-

lifted to the free troposphere over Asia, the time lag required for its decomposition could account for the 2t°Pb rich, but nitrate

over Asia Figure 5. Scatterplots of atmospheric nitrate (aerosol NO 3 plus HNO3) against 21°pb. Separate plots are shown for the samples collected near Asia and those from the remote western Pacific.

is advected

creating

nitrate.

NOx and NMHC

thermal decomposition

1992a, b; this issue]. and/or

poor, 0

and PAN

over the Pacific,

and atmospheric



retained

NO x far from its initial

et al.,

• •

cycle

(compare

in

6a and Hawaii Figures

tropospheric/lower

with little subsequent

A

Flights

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12

....

+

.........

I

200

300

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+,,

,*,,

100

150

I

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i

.........

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200

.........

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.....

1000

÷ "'

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1500

14 - 19 I

....

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t

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.........

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........

=l,,=,=li=,l

HNO 3 (pptv) 10

+ -

+

÷

2_°pb (fCi m "3)

,

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200 I

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__.+

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2

0 .........

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Figure

.........

I

.........

2OO

6, Comparison

I

3O0

of the altitude

I

0

I

50

distributions

100

of

21°pb

.........

I

150

200

and the major reactive

0

nitrogen

I

.........

I

500

species measured

PEM-West A. Sampling frequencies for the nitrogen species are much higher than the aerosol sampling; here have been averaged to correspond to the intervals represented by each aerosol sample. Geographic into near Asia (a) and remote western Pacific (b) subsets has been maintained.

.........

1000

during

data shown separation

I

1500

200

Fits

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6

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=. 8.5 km

Fits

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150

100

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Figure 7. Scatterplots depicted in Figure 6.

10 15 21°pb (fCi m 3 STP)

20

25

0

of atmospheric nitrate (NO3 plus HNO3) against

5

21°pb

10 15 2_°Pb (fCi m"3 STP) for the eight location/altitude

20

bins

25

300

Fits

-

6

-

13

=. 8.5

Fits

km

14

-

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2OO

[email protected]

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10 15 21°pb (fCi m "3STP)

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2O

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25

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5

Figure 8. As in Figure 7 but for peroxyacetylnitrate

• _

'

'

t

'

'

10 21°pb

'

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I

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15 (fCi

against 2'°Pb.

m "3 STP)

'

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20

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25

DIBB

ET AL.: ASIAN

INFLUENCE

OVER Flight

WESTERN

NORTH

PACIFIC

1791

2O ,I,i,l,,,I

I,,ll

,LLl=,,llllI==lel

00



_Be (fci m"a) 20'0

0 I

l

,

I

l

I

1

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i

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i

o' ' ';,'

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al,

,I

....

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....

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NO 3 (pptv)

' ' ,,,.I

'

....



I



''

....

I

....

HNOs (pptv)

1

' '16 ' ' Figure

scavenging.

Altitude

9.

with

distributions

altitude,

point in the history

.... '"

30

None of the soluble

NO 3 increased some

'

of _Be, 2t°Pb,

aerosol-associated

suggesting

species

they were

of this air mass when

16 NO3",

26

except

scavenged

at

2t°Pb and nitrate

were still present in the form of insoluble precursors. As we have seen, wet convection over continents appears the most likely mechanism that could enrich 21°Pb relative to other aerosolassociated

species

in free tropospheric

particular air mass, greater direct continental influence, altitude

correspond

air over the ocean.

In this

than one week removed from last atmospheric nitrate variations with

to those of 21°Pb.

and

Asia and in a narrower mote western Pacific.

The atmosphere over the Pacific Ocean just east of the Asian continent and in a broader region centered on Guam was sampled from the NASA a few weeks

AMES DC-8

in September

were spent in any given region,

- October

1991. Only

so the findings

must

be regarded as a series of snapshots of atmospheric composition that resulted from the specific meteorological conditions prevailing during the period of the PEM-West focused primarily on the composition

A mission. This paper has of aerosols. Despite the

Deep anism

Concentrations

of 7Be and soluble

ionic species

Pacific ocean. were quite low

air

precursors.

over Asia

scavenges

aerosols

without

depleting

As a result,

in the free troposphere, with those

I

....

....

I

10

20; '

J

....

I

15

20

Loa flyby.

appears

boundary

continental

to provide layer

air

a mech-

air to the middle

and

soluble

gases

turn

and

sparingly

from

the

soluble

to be correlated

asO3

in the

of Asia. It has recently been is low enough that deep wet

of modified

continental favors

rather

concentrations

of 2t°Pb. We hypothesize boundary

production

layer

of PAN

correlated

that the composition

air after

wet convective

of PAN over inorganic

NO3, at least

within the short periods of aging represented by the PEM-West A samples. It is likely that subsidence of this 2_°Pb- and PAN-rich subsequent

trations

accounting

2 and 14 km near

'

NO 3 reported from remote ocean islands. During PEM-West A, no relationships were found between 2t°Pb and inorganic nitrate

to the east results

between

'

convection could also lift NO_ rapidly into the free troposphere, which might account for the strong correlations between 2'°pb and

NO,

than expected

I

2t°Pb and O3 tended

air farther

higher

....

5

lift continental

in most aerosol samples collected in the free troposphere, both near Asia and farther east near Guam. In contrast, 2_°Pb concenwere

....

I

PAN (pptv) I

free troposphere 2- 5 days downwind suggested that the solubility of NO,

processing

over the western

1

i5o

and upper troposphere, where strong zonal winds can subsequently advect it over the Pacific. Intense precipitation in these systems

model relating deep wet convection downwind

"

altitude range near 8 km over the more reOzone concentration variations in the free

wet convection

to rapidly

short-term nature of the investigation the findings appear to be consistent over large geographic regions and with a conceptual of the free troposphere

'

in the boundary layer increased markedly when was advected over the ocean at low altitudes.

strongly

over Asia to the composition



I

troposphere tended to follow those of 2_°Pb. Concentrations of 2t°Pb and nearly all of the soluble aerosol-associated ionic species

cending

Conclusions

i

,

and NOy on flight 20, the Mauna

apparently Summary

'

; 0

PAN,

HNO3,

,

Y

loo



;o' '

....

0

NO (pptv)



' '60'o'' 'a;o

'400_

21°Pb (fci m)

and

in thermal

production

for the correlation

of

between

decomposition NO3

and

of PAN to

HNO 3, thereby

2t°Pb and nitrate.

1792

DIBB

It should during over its

be

the

fall

the Pacific minimum.

continental largely

larger

in

restricted

Asian

influence

summer

Pacific

"dust"

this of

on

be

expected

should

the

continental

scavenging

the composition

scheduled

revealed but

of the during

OVER

composition

influence

season,

precipitation

should

A was

herein

tracers

INFLUENCE

atmospheric

continental

during

those by

ASIAN

PEM-West

presented

even to

that

when

results

unaffected

western

mind

AL.:

to characterize

at a time The

influence

relatively

the

borne in order

ET

be at

significant impact air

was

that

are

processes.

Even

atmosphere

over

the

spring

and

season.

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over the western Pacific Results from PEM-WEST

Ocean during A, ,I. Geophys.

Tsunogal, S, T. Kurata, T. Suzuki, and K. Yokota, Seasonal variation of atmospheric z_°Pb and AI in the western North Pacific region, J. Atmos. Chem., 7, 389-407, 1988. J. D. Bradshaw and S. T. Sandholm, Georgia Institute of Technology, Atlanta, GA 30332. J. E. Dibb, R. W. Talbot, and K. 1. Klemm, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Morse Hall, 39 College Road, Durham, NH 03824-3525. G. L. Gregory, Atmospheric Sciences Division, NASA Langley Research Center, Hampton, VA 23665. H. B. Singh, NASA Ames Research Center, Moffet Field, CA 94035.

(Received Janurary accepted November

10, 1994; revised 25, 1994.)

November

17, 1994;