Oct 20, 1990 - from the launch of the NASA Space Shuttle and the Titan IV expendable launch ... (July), is localized near the launch site with peak levels not resolved by the ... (C) from Vandenberg AFB, California (34°N 121°W). 4. STEADY ...
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. Dll, PAGES 18,583-18,590, OCTOBER 20, 1990
The SpaceShuttle'sImpact on the Stratosphere MICHAEL J. PRATHER AND MARIA M. GARCIA NASA, GoddardInstitutefor SpaceStudies,New York ANNE R. DOUGLASS AND CHARLES H. JACKMAN
NASA, GoddardSpaceFlight Center, Greenbelt,Maryland MALCOLM
K. W. KO AND NIEN DAK SZE
Atmosphericand EnvironmentalResearch,Inc., Cambridge,Massachusetts
Launchof spacecraftusingsolidrocketmotorsleadsto releaseof gaseousandparticulatematterin the stratosphere.Concem over theseemissions,particularlychlorine,goesback to the Climatic Impact Assessment Program(Hoshizaki, 1975). The buildupof theseexhaustproductsand their perturbationto stratospheric ozoneis followed with two- andthree-dimensional atmosphericchemicaltransportmodels. Chlorine enhancements due to the currentrate of shuttlelaunchesis small, on averageless than 0.6% abovethe currentbackground.Other gasesemittedfrom the solid rocketsappearto have even smaller global effects,althoughthe impactof particulatealuminaremainsuncertain.
1.
INTRODUCTION
numericalmodelsof the stratosphere.Calculationshavebeen
The launchof NASA's SpaceShuttleand similar rockets made with two two-dimensional(latitude by altitude) models injects chlorine compoundsdirectly into the stratosphere, with completechemistry(AER model:Ko et al. [1985; 1989]; adding to the current burden of stratosphericchlorine. GSFC model: Douglasset al. [1989; Jackmanet al., 1989a] Depletionof the stratospheric ozonelayer hasbeenlinked to and a three-dimensional model for chemical tracers (GISS increasesin stratosphericchlorine compoundsassociated model: Prather et al. [1990]). In onenumerical simulation, Cly enhancements in the predominantly with chlorofluorocarbons (see recent two days after a Januarylaunch of the assessments: World Meteorological Organization (WMO) middle stratosphere [1986; 1990]; Watson et al., [1988]). The purposeof this Shuttleare still expectedto be clumpy,but the exhaustplume studyis to determinethe magnitudeof the chlorineincreases is predictedto have spreadovera regionabout20ø latitudeby
of about30 ppt (parts that might be causedby the SpaceShuttleand to assessthe 30ø longitudewith an averageincrease per 1012 ) or 2% above background. Onemonthlaterthe overallimpacton the chemistryandcompositionof the global Shuttle plume is well mixed, and increases in Clyarelessthan stratosphere. The solidrocketmotorson the SpaceShuttleand Titan IV 4 ppt throughoutthe stratosphere.The buildup of chlorine launch vehicles use a solid fuel composedof ammonium from these launchesapproachesa steady state limit after years:onaverage, Clywouldincrease byabout10ppt perchlorate,aluminumand a polymerbinder (P. D. Evanoff, several of the northernhemisphere,less Thiokol Corp., private communication,1989). The exhaust in the middle stratosphere consistsprimarily of gaseousHC1, carbonmonoxide,water than 0.5% above current levels. Correspondingozone vapor,molecularnitrogenand aluminumoxide. The potential depletionsare predicted to be less than 0.2% locally, with to the ozonecolumn. damageto the ozonelayer by the SpaceShuttle'ssolidrocket smallerperturbations The profiles and amounts of chlorineinjectedfrom the solid motorswasrecognizedduringtheClimaticImpactAssessment rocket motors are summarized in section 2. The transient Program (CIAP focussedon supersonicaircraft but also studied rocket plumes, see Hoshizaki [1975]). The last responseto a singlelaunchis shownin section3, and model
of the steadystateaccumulation of Cly are assessment of the Shuttlein termsof stratospheric ozonewas predictions morethana decadeago [Potter, 1978], andour understanding describedin section4. The overall impact on stratospheric of stratospheric chemistryand modellinghas evolved much chemistryand ozoneis discussedin section5. since then.
The
launch
scenario
considered
here
consists
of
2.
nine
CHLORINE FROM ROCKET EXHAUST
Estimates of the amount and distribution of chlorine released Shuttlesand six Titans per year; it is typical of the current schedule,but it may fall short of the frequencyneededfor from the launchof the NASA SpaceShuttleandthe Titan IV major spaceprojects. The chlorinefrom theselaunchesis expendablelaunchvehicle are availablefrom Thiokol (P. D. usedasa stratospheric source of Cly(totalinorganic chlorine:Evanoff, Thiokol Corp., private communication,1989). In the sumof HC1, C1,C12,C10, C1ONO2, andHOC1)in three Table 1 we reportthekilogramsof chlorine(asC1)releasedin 5 km vertical intervals for Shuttle launches from Cape Canaveral,Florida (nine per year) and for Titan IV launches Copyright1990 by the AmericanGeophysical Union. from bothCapeCanaveral(fourper year)andVandenbergAir ForceBase,California(two per year). The chlorineis released Papernumber90JD01452.
0148-0227/90/90JD-01452502.00
asHC1,whichwetreatasClyin themodels. 18,583
18,584
PRATHERET AL..' SPACESHUTFLE'SIMPACT ON THE STRATOSPHERE
The totalamountof chlorinereleasedinto the stratospherescalesresolvedby the model grid, and the calculations are (above15km) by thesolidrocketmotorsis 725,000kg (0.725 intended torepresent theaverage concentration of theresulting kilotons)per year, and can be comparedwith that associated nonuniformdistribution. Figures1 and 2 summarizethe with industrial halocarbons. The chemical industry's instantaneous increase inClyconcentrations at3.4mbar(about productionof halocarbonsexceeds1250 kilotons of chlorine 40 km altitude) asa function of latitudeandlongitude fordays per year [WMO, 1990]. The releaseof chlorineduring 2, 4, 8 and 30 followingboth the Januaryand July photochemicaldestructionof the chlorofluorocarbons (CFCs) initializations.Otherlevelsin the upperstratosphere show occurspredominantly in the stratosphere, but happensslowly, similareffects,but loweraltitudesin the stratosphere have ontimescalesof order100years,overthelifetimeof thegas. smaller absolute enhancements ofCly(seeFigures 3-5). The estimated annualsourceof stratospheric chlorinefromthe Aftertwodays(Figuresla and2a) theaverage increase in industrialhalocarbons is about300 kilotonsof chlorineper chlorine in theupperstratosphere, 50ppt(January) and70 ppt year(AERmodel);theremainder of theannualemissions goes (July),is localizednearthe launchsitewithpeaklevelsnot into the accumulatingatmosphericburden of chlorinated resolved by the modelgrid (8ø latitudeby 10ø longitude). halocarbons(about 600 kt/yr) or is destroyedin the After8 days(Figuresl c and2c)themaximum grid-averaged troposphere.Thus, the launchschedulein Table 1 would add levelshavedecreased by factorsof aboutfour (January) and onlyabout 0.25%to thecurrent stratospheric source of Cly. two (July),have movedaway from the launchsitein accord Theseresultsare qualitativelysimilarto a conclusionreached with the prevailingwinds,and have spreadover horizontal 16 yearsago [Ciceroneand Stealman,1974]. scalesthatareresolvedby themodel. For the Januarylaunch The release of chlorine from the 15 launches summarized in mostof theaddedchlorine(concentrations greaterthan1 ppt) Table 1 wasaveragedoverthe yearandput into themodelsas residesin the region boundedby 20øN-50øN and 40øWis lessdispersive, andfor a continuous source of Clyeverytimestep. Thevertical 100øW. The summerstratosphere distributionspecifiedin Table 1 wasusedby themodels. The theJulylaunch mostof theClyis contained between 20øN latitudinal location of the two launch sites was included in all 36øN and 150øE-140øW. Eight daysafter the January1 three models;but the longitudinallocationcould only be launch (Figure lc)thelargest grid-averaged perturbation toCly specifiedin the three-dimensionalsimulation. (asresolved by themodelgrid)is lessthan10ppt,about0.4% abovebackgroundlevels. Eight days after the July launch 3. TRANSIENT RESPONSE TO A SINGLE LAUNCH
(Figure 2c)theadded Clyremains moreconcentrated: greater
overa smallerarea. Onelaunchof the SpaceShuttleinjectsa single,very large than30 ppt (about1%) abovebackground One month after the Shuttle launch (Figures ld and2d), the pulseof 68,000kg of chlorineintothestratosphere. Although added chlorine is predicted to have spread over mostof the this amountof chlorineis inconsequential on a globally upperstratosphere in the northernhemisphere, andtheplume averaged scale,thegreatly enhanced levelsof Clyin the to havemixedthoroughly.Thewinterstratosphere vicinity of the exhaustplume may lead to large ozone is expected is dispersive and Cly perturbations are lessthan1 ppt depletionsover a spatiallylimited region. We examinedthe everywhere. In summer the exhaust productsremain transient response of stratospheric Clyto a singleShuttle launchusingthe three-dimensional GISS model. The chlorine predominantly over mid-latitudes (20øN-50øN) with still as largeas 3 ppt. The globallyaveraged is releasedoverCapeCanaveral(29øN,80øW)by usingone- perturbations depletion of ozone associated with a singlelaunchshouldbe ninthof the annualsourcegivenin Table 1 asaninstantaneous lessthanthatcausedby thesteadystatebuildupof chlorine,as source. Simulationswere initiated on January1 and July 1, and discussedbelow. Local destruction of ozone in the immediate largerand continuedfor onemonth. Immediatelyfollowingthe launch, vicinityof therocketplumecouldbe significantly the exhaustplume will not be completelymixed over the is not explicitlyresolvedin theseglobalmodels. 4.
TABLE 1. Stratospheric ChlorineReleasedAnnually by Shuttle and Titan IV Launches
The
three
STEADY STATE ACCUMULATION
models
used
the
continuous
source
of
stratospheric chlorinefrom the rocketlaunchesas describedin
section2. Theultimateremovalfor theinjectedstratospheric Kilogramsof Chlorine(as C1) Altitude, km
15-20 20-25 25-30 30-35 35-40 40-45 45-50
A
176,800 136,100 109,600 87,400 69,300 25,900 4,500
B
C
16,800 14,700 12,600 10,600 8,900 7,300 6,000
8,400 7,300 6,300 5,300 4,500 3,700 3,000
Clyistransport intotheloweratmosphere (troposphere) where most inorganicchlorine speciesare soluble and therefore removedrapidly by rainfall and other processes.In these modelsthissinkwasappliedby imposing eitherrapidlossfor
Clybelow10 km (two-dimensional models) or a negligibly smallconcentration of Clybelow1 km (three-dimensional model). Small differencesin the applicationof this lower boundary conditiondo not affectthecalculated stratospheric
Clydistribution, because almost allof thechlorine transported into the troposphereis removedand cannotbe recirculated backinto the stratosphere. These calculations were initiated and then continued for
several model years until a steady state distributionwas
In steady state, stratospheric Clyadditions havebuilt The launchscenarioassumes nineShuttles(A) andfourTitans reached. (B) fromCapeCanaveral,Florida(29øN80øW)andtwo Titans up until the amountof chlorineinjectedintothe stratosphere (C) from Vandenberg AFB, California(34øN 121øW). equalsthattransported intothe lowertroposphere.
PRATHER ET AL.' SPACESHUT•LE'SIMPACTONTHESTRATOSPHERE
18,585
GISS Cly (ppf) 3.4 mb Jonuory 90
i
i
i
i
i
60
F
50
-30 -60
_4 days
_2 days
(b)
(a) -90
I
90
I
I
I
I
I
60
_
30
-
I
H 0.48 H
I
H0.45 H _
0.55
0.57
0
-30 -60
_8 days
-9O
-180
I -90
_,50 days
(c) I 0
,I 90
180
Longitude
-180
I -90
(d) I 0
I 90
180
Longitude
Fig. 1. Latitudeby longitude contours of chlorine enhancements near40 km altitudedueto a singleShuttlelaunchon January 1. Results fromtheGISSmodelareshownfor (a) 2, (b) 4, (c) 8, and(d) 30 daysfollowingthelaunch.
a factorof 2 or greater belowthe Thecomputed addition to Cly(ppt)associated withthe as6 ppt,andaregenerally
enhancements in thenorthernstratosphere. Shuttle/ Titan launchesis shownas monthly, zonal averages corresponding in Figures3-5 for the GSFC, AER and GISS models,
Duringnorthernwinter,all modelsshowrapidnorthward
respectively. Themagnitudes of theClyincrease islargest in mixingbetween30øNandthe Pole,with isolinesthat slant
anddownward. Thisbasicpattern shown in Figures northemmid-latitudes(30øN-50øN) nearthe source,andpeaks poleward stratospheric tracers, both in theupperstratosphere (30-45 km altitude)wheretherocket 3a-5a is typicalof otherlong-lived emissions arelargeston a molecule permoleculeof air basis. from model calculations [Jackman et al., 1989b] and
Increased concentrations of Cly in the northernupper observations(see recent assessments:WMO [1986]). The
stratosphere rangefrom 6 to 14 ppt in the GSFC model pattern ofClyduring northern summer, however, dramatically sourcein a (Figure3), 4 to 9 pptin theAER model(Figure4), and6 to showsthe impactof a localizedstratospheric season without substantial latitudinal mixing. The increases in 12 pptin theGISSmodel(Figure5). TheGSFCandGISS
in July(Figures 3b-5b)peakstrongly at models predicta similarbuildupof Cly;the AER model Clyconcentration appearsto have a more rapid stratospheric circulation 30øN between 30 and 50 km altitude in all three models, with maximaof morethan12 pptin [Jackmanet al., 1989b] that flushesout the chlorinemore monthlyandzonallyaveraged the GSFC and GISS models, and 9 ppt in the AER model. rapidly.In thelowerstratosphere (15-25km altitude) Cly concentrationsare less enhanced: about 2 ppt at 15 km
In orderto determine therelative perturbation to Clyfrom
modelscomparedthe increasing to about6 pptat 25 kin. Severalyearsarerequired therocketlaunches,the two-dimensional to transport substantial concentrations of therocketsourceof calculated Clyenhancements (Figures 3-4) withthe Cly calculatedfrom all othersources:the CFCs, CC14,CHF2C1, Clyintothesouthern hemisphere stratosphere. Enhancements in the southern stratosphere rangefromlessthan1 to asmuch CH3CC13, CH3C1.Air enters thestratosphere containing a mix
18,586
PRATHERET AL.' SPACESHU'I•LE'S IMPACT ON THE STRATOSPHERE
Cly (ppf) 3.4 mb July
GISS 90
I
I
I
I
I
5
-30
-6O
_2 days
-9O
_4 days
(a)
I
I
m
(b)
I
I
I
I
90 60
30
-30 -60
_8 days
-90
-1BO
_30 days
(c)
I
I
I
-90
0
90
180
-1BO
(d)
I
I
-90
0
Longitude
90
180
Longitude
Fig. 2. Latitudeby longitudecontours of chlorineenhancements dueto a singleShuttlelaunchon July 1. SeeFigure1.
60
GSFC 01¾(ppt) Jon
GSFC Cly (ppf) July
50
40
•
30
2o
•oI(o) 0 -90
I -60
I -30
0
;50
60
90
-90
(b)
Latitude
-60
-30
0
;50
60
90
Latitude
Fig.3. Latitudeby altitude(pressure) contours of enhanced chlorine (in ppt)fromtheGSFCmodel.Thesteadystate
buildup ofchlorine asClyis.caused bythelaunch ofnineShuttles andsixTitan IV vehicles peryear.Themonthly and zonallyaveragedconcentrations are shownfor (a) Januaryand(b) July.
PRATHERET AL.' SPACESHLrI'FLE'SIMPACT ON THE STRATOSPHERE
AER ely (ppt) Jan
6O
18,587
AER C{y(ppt) July I
I
I
I
I
I
i
-60
-30
0
50
60
90
I
5O
4O
5O
2O
0 -90
I -60
I -30
0
30
60
90
-90
Lafifude
Lafifude
Fig. 4. Latitudeby altitude(pressure)contoursof enhancedchlorine(in ppt) from the AER model. See Figure 3.
OlSSely (ppt)
$0
50
Jan
ely (ppt) July
GISS
I
_
40
5o
2O
10
(b) o -90
i -60
i -30
i 0
Lafifude
I
I
30
60
-90
I
I
I
I
I
-60
-30
0
30
60
9O
Loftrude
Fig. 5. Latitudeby altitude(pressure)contoursof enhancedchlorine(in ppt) from the GISS model. See Figure3.
of thesehalocarbons representing thebulk tropospheric mixing hemisphere, Clyincreases arelessthan0.2%for theGSFC ratiosof thesespeciesandwith negligibleconcentrations of the model and 0.1% for the AER model. more solubleinorganicchlorine(Cly). In the lower Ozone perturbationsat steady state associatedwith the
stratosphere Cly concentrations are smallbecause only a source of Clyfromrocketlaunches areshown in Figure8 for The largest depletions in ozone fractionof the CFCs have been photochemically destroyed, the GSFC model. between0.10% and 0.15%, occurin the upper therebyreleasingchlorineatoms. In the upper stratosphere concentration, (30-45 km altitude)in the northernmid-latitudes. where the halocarbonand CFC concentrationsare greatly stratosphere reduced,Cly concentrations approach their upperlimit, Losseselsewhereare much smallerwith the exceptionof the currently about3 ppb(parts per109).Thescenario forrocket correspondinglocationsin the southernhemisphere. The launchesin Table 1 leads to only modestperturbationsin depletionof the total columnabundanceof ozoneis likewise stratospheric Cly,asshown in Figures 6 (GSFC)and7 (AER). small, less than 0.1%. The photochemicalmodel usedhere The GSFC resultspredictincreases rangingfrom 0.3 to 0.6% includesonly gasphase,homogeneous chemicalreactions;it over the northernmid-latitudes;while the AER model gives doesnot accountfor the heterogeneous reactionsoccurringon smaller enhancements, 0.2 to 0.3%. In the southern polar stratosphericclouds that have been shown to be
18,588
PRATHERET AL.: SPACESHU'ITLE'S IMPACT ON THE STRATOSPHERE
GSFCACI¾(%) Jan
60
ly (]%)July
GSFC
50
4O
3O
2O
10
(a) o -90
-60
(b) -,50
o
5o
60
90
-90
-60
-5o
Latitude
o
5o
60
90
Latitude
Fig.6. Latitude by altitude (pressure) contours of theperturbation to background Clylevels(%) fromtheGSFCmodel. See Figure 3.
6O
5O
•
AER ACly(%) July
AER 6Cly (%) Jan ,
I I I I I
I
I
I
I
I
-60
-30
0
30
60
I
30 20
•0
0 -90
i -60
i -50
0
50
60
90
Latitude
-90
90
Latitude
Fig.7. Latitude byaltitude (pressure) contours oftheperturbation tobackground Clylevels(%)fromtheAERmodel.See Figure 3.
responsible for the chlorine-catalyzed destruction of ozonein
rate of about300 kt/yr. Global stratospheric modelsare used thelowerstratosphere duringpolarwinter(theAntarcticozone here to assessthe impactof the currentlymodestlaunch
hole). Nevertheless, the impactof Shuttlechlorineon further scheduleon stratospheric chemistryand ozonedepletion. polarozonelosscanprobablybe constrained sincethe relative In the immediateexhaustplumeof the Shuttle(about40 m of HC1 are perturbations to Clyin thelowerstratosphere arelessthan acrossin the upper stratosphere),concentrations 0.1% over Antarctica and 0.5% over the Arctic. large,about0.08 by volume. Even if thisplumeweremixed 5.
THE POTENTIAL FOR OZONE DEPLETION
Each launchof the SpaceShuttleinjectsabout0.068 kt of chlorineinto the stratosphere. This amountis smallcompared to the currentbackgroundof stratospheric chlorine(3 ppb), which is generatedfrom the photochemicaldestructionof industrialandnaturalhalocarbons within the stratosphere at a
over a 10 x 10 km area, concentrationswould still exceed
1000ppb. However, a 100km2 areacomprises lessthan 1/1,000,000of the mid-latitudestratosphere, andthe globalor evenregionaleffectsof completeozonedestruction withinthis corridorwouldbe inconsequential. Furthermore, the chlorine is releasedpredominantlyas HC1 and wouldneedsometime to be chemicallyprocessed intomorecatalyticallyactiveforms
PRATHERET AL.' SPACESHUTrLE'S IMPACT ON THE STRATOSPHERE
6SFC A03 (%) July
SFC
60
18,589
50
40
30
20
'øI( o -90
I -60
I -30
I 0
I 30
I 60
90
-90
Latitude
-60
-30
0
30
60
90
Latitude
Fig. 8. Latitudeby altitude(pressure)contoursof the perturbation to ozone(%) from the GSFC model. SeeFigure3.
(C1orC10). Thepathof theShuttle isnotvertically aligned,lowerbackground levelsof Cly. Eventhemostoptimistic thecorridor of exhaust gases is spread overlateral extent of controls overhalocarbons would notleadtoClyconcentrations more than a 1000 km in a day, and thus no local hole in
less than 2 ppb much before the end of the twenty-first
column ozone could occur above the launch site.
century.
0.2 ppboutof morethan2 ppbCly). In orderto havea
The ShuttleandTitan IV solidrocketmotorscomprisethe largestsourceof stratospheric chlorinethat is expectedfrom the currentspacefleet. The major launchvehiclesfrom the United Statesand other spaceagenciesuse nonchlorinated (e.g., liquid) fuels or employmuchsmallerrockets. The U.S. strategic nucleararsenalusessolidfuelcontaining chlorine,but
chlorine levels over such an area is modest, at most +5%
about thesame in mixingratioasthatto Cly,andwouldnot
This early stage following the launch is not adequately modeled in these calculations, but we believe that strict limits
can be placed on the potentialfor global ozone destruction becausethe amountof chlorineinjectedis small compared with thatcontainedin a 1000km by 1000km region(lessthan
significantimpacton ozoneglobally,the plumemustmix with in such launches most of the chlorine would be released below the stratosphericenvironment and lead to significant 15km. The exhaust from the solid rocket motors also contains other perturbations over scalesof at least 1000 x 1000 km. In thefew daysfollowinga launch,stratospheric windswill possiblestratospheric pollutants.The majorgaseous compohave stretchedand dispersedthe exhaustplume to scales nentsareCO (24% by wt), HC1(21%),H20 (10%),N2 (9%), greaterthan 1000 km. The averageincreasein stratosphericCO2 (4%) and H2 (2%). The perturbation to CO shouldbe
affectthe background levelsof order100 ppb. within a 20ø latitudeby 20ø longitudearea. By the endof the significantly month,theseperturbations decreaserapidlyto lessthan0.2% Clearly,the HC1represents the largestfractionalperturbation above backgroundlevels as the chlorineis mixed laterally to thebackground stratosphere; theremainingeffluentsshould throughoutthe stratosphere. havenegligibleimpacton the stratosphere. A continuous seriesof rocketlauncheswill leadto a buildup Anotherprincipalexhaust product, particulate A1203(30%), chemistry.Most of of chlorinein the stratosphere whosemagnitudeis governedby has the potentialto perturbstratospheric the frequencyof launchesand the rate of the stratosphere- the alumina is reportedby Thiokol Corporationto form troposphere circulation.For a scenario of nineShuttleandsix particlesof radii greaterthan 1 micron;thesefall out of the TitanIV launches peryear,theaccumulation of chlorinein the stratosphere morerapidlythanthegaseous products whichare stratosphere is still modest,rangingfrom 0.2 to 0.6% over removedby the circulationexchangingair betweenthe northernmid-latitudesand much less in the tropicsand stratosphere andtroposphere (modeled here).Thestratospheric southernhemisphere.Corresponding ozonedepletionsare abundance of largeraluminaparticlesappears to be increasing evensmaller,lessthan0.25%locallyandlessthan0.1%in the andhasbeenattributed to solidrocketmotorsaswell asspace total column. debris[Radkeet al., 1982;Zolenskyet al., 1989].
Theaddition of Clyto thewinterpolarstratosphere is of
Atmospheric measurements ofSpace Shuttle exhaust [Cofer
particular interestbecause of therole thatchlorineplaysin et al., 1987]indicate thatabouthalfof themassof A1203 is in creatingtheAntarcticozonehole;buttheexpected buildupat particleswith radii less than 1 micron and thus might
thepoles represents onlya smallfractional increase tocurrentaccumulate inamanner similar toClyinthese calculations. A levels. In the future,we mighthopethatstringentcontrolson simplescaling(i.e., Cofer et al. [1987] size distributionto a
industrial production of halocarbons, as envisaged by the maximum of 10pptClyin thelowerstratosphere) givesan Montreal Protocol, wouldreverse thecurrent trendandleadto upperlimitof 0.001particles percm3 withradiigreater than
18,590
PRATHERET AL.: SPACESHUTFLE'SIMPACTON THE STRATOSPHERE
0.1 micronas comparedto background sulfatelevelsof order Jackman, C. H., R. K. Seals,Jr.,andM. J. Prather, Two-dimensional
1percm3. Thecorresponding surface area is14x10 42cm2per
intercomparison ofstratospheric models, NASA Conf. Publ. 3042,
cm 3. These alumina particles mayactasnuclei forice Ko,1989b. M. K. W.,
K. K. Tung, D. K. Weisenstein,and N. D. Sze, A
deposition in thelowerstratosphere [Turcoet al., 1982]. zonal mean model of stratospheric tracer transport inisentropic Observationalevidence[Cofer et al., 1984] and laboratory
coordinates: numerical simulations fornitrous oxideandnitricacid,
studies suggest thatalumina particles reactwiththeHC1in the
J. Geophys. Res., 90,2313-2329, 1985.
exhaust toform chlorides and may provide active sites forCly-Ko, M.K.W., D.Sze, and D.inK. Weisenstein, roles of dynamics andN. chemical processes determining theThe stratospheric
NOyheterogeneous reactions inthelower stratosphere. Thus concentration ofozone in1-Dand 2-Dmodels, J.Geophys. Res., the buildupof smallparticlesin the lower stratosphere may 94, 9889-9896,1989. enhancebothprecipitation (dehydration or alenitrification) and Potter,A. E., Environmental effects of theSpace Shuttle, J. Environ.
ozonedestruction in thelowerstratosphere. Theroleof
Sci.,21, 15-21, 1978.
particulates from solid rocket motors inthechemistry ofthePrather, M.,M.M. Gatera, R. Suozzo, and D.Rind, of the Antarctic ozone hole: Dynamical dilution withGlobal a 3-D impact chemical stratosphere is not well characterized today,andfurther transport model, J.Geophys. Res., 95,3449-3471, 1990.
researchwill be neededfor a reliable assessment of future Radke,L. F., P. V. Hobbs,andD. A. Hegg,Aerosols andtracegases in the effluentsproducedby the launchof large liquid- and solidimpacts. Acknowledgments. This reportrelieson the technicalinformation suppliedby theThiokolCorporation, in particular, thecontributions of
fueledrockets,J. Appl. Meteorol.,21, 1332-1345, 1982. Turco, R. P., O. B. Toon, R. C. Whitten, and R. J. Cicerone,Space Shuttle ice nuclei, Nature, 298, 830-832, 1982.
Watson, R. T., M. J. Prather, and M. J. Kurylo, Presentstate of knowledgeof the upper atmosphere1988: an assessment report the issue of particulatealumina and acknowledgethe supportof (NASA's Upper AtmosphereResearchProgram'sReport to the NASA's Upper AtmospherePrograms. Congress),NASARef. Publ. 1208, 208 pp., 1988. World Meteorological Organization, Atmospheric ozone 1985: REFERENCES Assessmentof our understandingof the processescontrollingits presentdistributionandchange,Global OzoneRes.andMonitoring Cicerone,R. J., and D. H. Stealman,The SpaceShuttleand other P. Evanoff and J. Hinshaw. The authorsthank C. Kolb for insighton
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(ReceivedJune23, 1990; acceptedJuly 3, 1990.)
