MOZART, a global chemical transport model for ... - Wiley Online Library

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103,NO. D21, PAGES 28,291-28,335,NOVEMBER 20, 1998

MOZART, and

related

2o Model

a global chemical transport model for ozone chemical results

and

tracers evaluation

D. AoHauglustaine, •'2 G. P. Brasseur, • S. Walters,• P. J. Rasch, J.-F. Mfiller,• L. KoErnrnons• TMand Mo A. Carroll4 Abstract.

In this secondof two companionpapers, we presentresultsfrom a new

globalthree-dimensional chemicaltransportmodel,calledMOZART (modelfor ozoneand related chemicaltracers). MOZART is developedin the frameworkof the NationalCenterfor AtmosphericResearch(NCAR) CommunityClimate Model (CCM) and includesa detailedrepresentation of tropospheric chemistry.The model providesthe distribution of 56 chemicalspeciesat a spatial resolutionof 2.8ø in both

latitude and longitude,with 25 levelsin the vertical (from the surfaceto level of 3 mbar) and a time stepof 20 min. The meteorological informationis suppliedfrom a 2-year run of the NCAR Community Climate Model. The simulated distributions

of ozone(03) and its precursorsare evaluatedby comparisonwith observational data. The distributionof methane,nonmethanehydrocarbons (NMHCs)• and CO are generallywell simulatedby the model. The model evaluationin the tropics stressesthe needfor a better representationof biomassburningemissionsin order to evaluatethe budget of carbonmonoxide,nitrogenspecies,and ozonewith more accuracyin theseregions.MOZART reproducesthe NO observationsin most parts of the troposphere.Nitric acid• however••s overestimatedover the Pacific by up to a factor of 10 and over continentalregionsby a factor of 2-3. Discrepancies are also found in the simulationof PAN in the upper troposphereand in biomass burningregions.Theseresultshighlightshortcomings in our understandingof the nitrogenbudget in the troposphere.The seasonalcycleof ozone•n the troposphere •s generallywell reproducedby the model in comparisonwith ozonesoundings. MOZART tends,however,to underestimate03 at higherlatitudes,and specifically above 300 mbar. The global photochemicalproductionand destructionof ozonein

the troposphere are3018Tg/yr and2511Tg/yr, respectively (net ozoneproduction of 507Tg/yr). The stratospheric influxof 03 is estimatedto be 391Tg/yr and the surfacedry deposition898 Tg/yr. The calculatedgloballifetime of methaneis 9.9 years in the annual average. selected model results regarding the distribution of

1. Introduction

In a companionpaper[Brasseuret al., this issue],a newthree-dimensional (3-D) chemicaltransportmodel (CTM) of theglobaltroposphere calledMOZART (Model for ozoneand related chemicaltracers) was de-

troposphericozone(03) and its precursors,methane (CH4), nonmethanehydrocarbons(NMHCs), carbon monoxide(CO) and nitrogenoxides(NO•), to evalu-

ate these results relative to existing observationsand, finally, to presentthe simulatedglobal budget of troposcribed.The purposeof this secondpaper is to present spheric 03. The analysisof the results provided by a global troposphericmodel is more complicatedthan the equivalent analysis for a stratosphericmodel. Concen•National Center for Atmospheric Research, Boulder, trations of chemical compoundsare much more variColorado. able below the tropopause than above this boundary 2Also at Service d'A•ronomie du Centre National de la due to the importance of subgrid scale processes,inRecherche Scientifique, Paris. cluding convectivetransport, precipitation, and strong 3BelgianInstitute for SpaceAeronomy,Brussels. 4Department of Atmospheric, Oceanic and Space Sci- coupling between the surface and the atmosphere. In ences,University of Michigan, Ann Arbor. addition, available observationsare sparseand, in many cases, cover only a small fraction of the troposphere. Copyright 1998 by the American Geophysical Union. The current version of MOZART, driven by physical and dynamical variables provided by a general circulaPaper number 98JD02398. 0148-0227 / 98/ 98JD-02398509.00 tion model (GCM), representstypical conditionsas op28,291

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HAUGLUSTAINE ET AL.: MOZART, MODEL RESULTS AND EVALUATION, 2

Table 1. RegionsUsed in Vertical Profile Comparisonsof NO, HNO3, PAN, H202, and AcetoneMeasurements From GTE Expeditions With Model Results Grid

Latitude

Longitude

Expedition

Date

July 7 to August 17, 1988 July 6 to August 15, 1990 July 6 to August 15, 1990 July 6 to August 15, 1990 September 16 to October 21, 1991 September 16 to October 21, 1991 September 16 to October 21, 1991 September 16 to October 21, 1991 February 7 to March 14, 1994 February 7 to March 14, 1994 February 7 to March 14, 1994 September 21 to October 26, 1992 September 21 to October 26, 1992 September 21 to October 26, 1992 September 21 to October 26, 1992 August 15 to September 20, 1996 August 15 to September 20, 1996

Alaska

55øN-75øN

170øW-155øW

ABLE

Canada, Ontario US coast, East

45øN-60øN 35øN-45øN

90øW-80øW 80øW-70øW

ABLE 3B ABLE 3B

3A

Labrador North Pacific

50øN-55øN 15øN-35øN

60øW-45øW 180øW-150øW

ABLE 3B PEM-West

China coast, East Japan coast, East Philippine Sea China coast, East Japan coast, East Philippine Sea Africa, South Atlantic, South Africa coast, West Brazil, East Fiji Tahiti

20øN-30øN 25øN-40øN 5øN-20øN 20øN-30øN 25øN-40øN 5øN-20øN 25øS-5øS 20øS-0ø 25øS-5øS 15øS-5øS 30øS-10øS 20øS-0ø

115øE-130øE 135øE-150øE 135øE-150øE 115øE-130øE 135øE-150øE 135øE-150øE 15øE-35øE 20øW-10øW 0ø-10øE 50øW-40øW 170øE-170øW 120øW-100øW

PEM-West A PEM-West A PEM-West A PEM-West B PEM-West B PEM-West B TRACE A TRACE A TRACE A TRACE A PEM-Tropics A PEM-Tropics A

A

Reference

1 2 2 2 3 3 3 3 4 4 4 5 5 5 5 6 6

References:1, Harriss et al. [1992];2, Harriss et al. [1994];3, Hoell et al. [1996];4, Hoell et al. [1997];5, Fishman et al. [1996];Hoell et al. [1998].

posedto specificmeteorologicalsituations. Therefore climatological observations availableoverlongtime periods will be usedfor ozone,surfacemethane and nonmethane hydrocarbons, and surface carbon monoxide when available to evaluate the model results.

For ni-

the semi-Lagrangian transport scheme of Williamson

andRasch[1994]),convective transport(usingthe formulationof Hack [1994]adoptedin CCM-2), diffusive exchangesin the boundary layer (based on the parameterizationof Holtslagand Boville [1993]),chemi-

trogen speciesthe climatologiescompiledby Emmons cal and photochemicalreactions, wet deposition of 11 et al. [1997]from publiclyavailabledata setsare used. solublespecies,and surfacedry deposition.The chemFor the purposeof this paper, only aircraft data from ical schemeincludes140 chemicaland photochemical the mergedGTE (Global Tropospheric Experiment) reactions and considersthe photochemicaloxidation archiveare considered,and regionalgrids are defined schemes of methane(CH4), ethane(C•H6), propane to providemean vertical profiles. Table I providesthe (C3H8),ethylene (C2H4),propylene (C3H6),isoprene

gridsconsidered, their location,and the corresponding(C5H8),terpenes (asc•-pinene, C10H16), anda lumped GTE campaign. The climatologiesof Emmons et al. compound n-butane(C4H10)usedas a surrogatefor [1997]havebeen modifiedto includemeasurements of other _•C4hydrocarbons. The evolutionof species is HNO3, PAN, H20•, and acetone. calculatedwith a numericaltime stepof 20 min for both Version I of MOZART

is described in detail in the

companion paper and only a brief overview is provided here. Dynamical and other physical variables neededto calculatethe resolvedadvectivetransport as well as smaller-scale exchanges and wet scavenging are precalculatedby the National Center for Atmospheric

chemistry andtransportprocesses. In itspresent configuration the modelis run with a spatialresolutionwhich is identicalto that of CCM (triangulartruncationat 42

waves,T42) with a corresponding numerialgrid of 64 Gaussian latitudes and128equidistant longitudes (corresponding to abouta 2.8øx2.8øhorizontal resolution). Research (NCAR) CommunityClimateModel(CCM) In the verticalthe modeluseshybridsigma-pressure coand providedevery3 hoursfrom preestablished history ordinateswith 25 levelsextendingfrom the surfaceto tapes. The versionof CCM usedin the presentstudy the levelof 3 mbar. MOZART hasbeenintegratedus-

(CCM-2, Ft0.5library) is intermediatebetweenCCM-2 [Hacket al., 1993]andCCM-3[Kiehlet al., 1996].The MATCH modeldescribed by Raschet al. [1995,1997] formsthe meteorological componentof MOZART. In MOZART the time historyof 56 chemicalspeciesis cal-

ing a 2-year simulation of the CCM. Initial conditions

for chemical species are takenfromprevious runsperformed with slightlydifferentversionsof MOZART. A total of about 10 years have been simulatedwith the

CTM. The resultsobtainedduringthe lastyearof inte-

culated on the global scalefrom the surfaceto the mid- grationare considered for analysisand interpretation. dle stratosphere.The model accountsfor surfaceemisThe globaldistributions of CH4andNMHCsarepresionsof chemicalcompounds(N20, CH4, NMHCs, CO, sented and compared to observationaldata in section

NOx, CH•O, and acetone),advectivetransport(using 2, and the distribution of CO is evaluated in section

HAUGLUSTAINEET AL.' MOZART, MODEL RESULTSAND EVALUATION, 2

28,293

CH4 - Zonal Mean - July - ppmv

3. The simulated radicals, carbonyl compounds, and

peroxidedistributionsare illustrated in section4, and section5 is devotedto nitrogen species. The distribution and budget of ozone are presentedin section 6. Finally, concludingremarksregardingthe evaluationof MOZART are given in section7.

2. Methane and Other Hydrocarbons Since the atmosphere is an oxidizing environment,

•

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'••',.•o•: •. •_._-

• •.o0•J methaneand nonmethanehydrocarbons(NMHCs) are < 10 graduallydegradedthrough a sequenceof radical and nonradical carbony! compounds. In the process,hydrocarbonsprovide an essentialfuel for photochemical productionof ozone. Methane, the simplesthydrocar-50 0 50 LATITUDE bon, hasthe highestatmospheric abundance(about 1.8 ppmv) and becauseof its low reactivityand hencelong •iDu•e 2. Zo•lly •e•ed me••e •i• •o c•oss lifetime (approximatelyl0 years)is distributedalmost sec•o• (pp•) cMcul•ed fo• July co•d•o•s. D•s•ed homogeneously throughoutthe troposphere. l•e •d•c•es •odel •opopAuse. Transportof long-livedtracersbetweenthe two hemispheres,a much slowerprocessthan transport along the zonal and vertical directions,takes place on a char- hemisphere(about 80% in our model;see Brasseuret acteristictimescaleof about 1-2 years [Jacobet al., al. [thisissue]),this hydrocarbonprovidesinformation 1987; Milllet and Brasseur,1995]. Sincea large frac- about global scaletransport including interhemispheric tion of methane emissionstakes place in the northern

CH4 Mixing Ratio Deviation - January i

300

....

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(NOAA/CMDL) networkat selectedstations[Steeleet al., 1987]. In order to focuson the interhemispheric

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CH4 Mixing Ratio Deviation - July 500 250 200 150 100 A

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exchanges.The latitudinal gradient in the zonal mean methane surface concentration, calculated for January and July is compared in Figure I with data provided by the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory

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Figure 1. Observed(triangles)methanesurfacemixing ratio at selectedCMDL stations[Steeleet al., 19871 and calculated(solid line) zonal mean surfacemixing ratio (expressed as departurefrom value at the South Pole) for Januaryand July (ppbv).

gradient, while ignoring the possible long-term trends in both the data and the model, results are expressed as deviations from the surfacemixing ratio at the South Pole. As seen in Figure 1, the interhemisphericdifference in the surfacemixing ratio is closeto 200 ppbv in January, in agreement with observational data. It is reduced to 130 ppbv in July when oxidation of methane by OH is enhanced in the northern hemisphere. The calculated zonal mean distribution of methane mixing ratio, shown for July in Figure 2, is characterized by high values near the surface at high latitudes in the northern hemisphere where most of the surface emissions take place and by a rather uniform mixing ratio throughout the tropospherein the southernhemisphere. Efficient upward transport is visible in the tropics. A marked horizontal gradient in the methane mixing ratio is simulated in the lower stratosphere in the subtropics as a consequenceof rising motions in the tropics and subsidenceat high latitudes. A sharp vertical gradient is also obtained at the tropopause and in the lower stratosphere where the distribution is controlled more strongly by photochemistry.

The calculated annual mean methane lifetime (defined as CH4/LcH4, where LcH4 is the photochemical lossof methane) in the global troposphereis 9.9 years in MOZART. Figure 3 showsthat over a seasonalcycle this calculated lifetime varies from 6 years in July to

28,294

HAUGLUSTAINE ET AL' MOZART,MODELRESULTSAND EVALUATION,2 but underestimatesobservationsby up to a factor of 2 in the free troposphere. In the southern hemisphere

MOZART CH4 Lifetime

the calculated abundance of C2H6 is a factor of 2 lower 15 %

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than observations,suggestingthat the model underestimatesthe biomassburning emissionsof this compound in the tropics or its export out of the boundary layer, or that air massesencounteredby the aircraft during this particular flight were influencedby local emissions

[Boissard et al., 1996].In the caseofpropane(Figure5) the model underestimates

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Figure 3. Seasonalcycle of methane photochemical chemicallifetime (years) calculatedfor the northern

the concentrations

measured

duringthe TROPOZ experiment.For both compounds the measurementsseem to be strongly influencedby continental sources,while the model values along the flight track seemto be mostlyrepresentative of oceanic conditions.

During winter, in the marineboundarylayer overthe hemisphere (dashedline), southernhemisphere (dotted Atlantic, the calculatedC2H6 rangesfrom 0.5-1 ppbv line), and globallyaveraged(solidline). in the tropics to 2-3 ppbv at 60øN and reachesa maximum of 3-5 ppbv over the continentsat the surface. Similarly,overthe Atlantic Oceanthe calculatedC3H8

16 years in January in the northern hemisphereand from 9 years in January to 17 years in July in the southern hemisphere, due to enhanced oxidation dur-

MOZART C2H6 (TROPOZNS FLIGHT)- Jonuory- ppbv

ing summertime.Prinn et al. [1995]deriveda global

', .....

methane lifetime of 8.9+0.6 years basedon an analysis of methylchloroformobservations.The model overestimates this value by about 10%. The global burden of

i , , , i , , , I , , , i , , , i ,_•

8

CH4inthemodel is3613TgCH4(ratioof1.03between northernand southernhemispheres). Non-methanehydrocarbons(NMHCs) are more re-

,., 6

active than methane and have smaller emission rates,

% 4

making their atmosphericabundancesmallerwith more localized maxima near emissionsourcesand higher spatial and temporal variabilities. NMHCs play an important role in terms of ozone photochemicalproduction in many regions of the tropospherewhere fossil fuel, biogenic,or biomassburning emissionsare large. The airborne tropospheric ozone campaigns experiment (TROPOZ II) conductedin January 1991 has provided the meridional distributions of several light

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TROPOZ II / WESTERN FLIGHTS - ETHANE (ppb) -60 -50 -40 -30 -20 -10

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hydrocarbons (e.g., C2H6, C3H8) between70øN and

50

60

70 lO

60øS. The most important emissionsof ethane and

-9

9

propaneare associatedwith fossilfuel (natural gas)

-8

and biomassburning. Their lifetime regarding oxida-

E

tion by OH rangesfromseveralmonthsin winterto lessthana monthin summer for C2H6,andfrom1-2

• 6-

months in winter to a week in summer for C3H$. Fig-

_ 5-

ures 4 and5 compare thecalculated distributions of

60

LATITUDE

-7 -• -6

C

-5 m

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/

-4

ethane and propane, respectively,with the observations

3

obtainedby Boissardet al. [1996]during the south-

2

•]

bound flights of TROPOZ. The model resultshave been 1 sampled along the TROPOZ southboundflight track 0 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 (i.e., west coast of Canada, westernNorth Atlantic, LATITUDE west coast of South America) and monthly averaged for the period of the campaign. In the northern hemi- Figure 4. Monthly meanethanemixingratio(ppbv) spherethe calculatedconcentrationof ethane (Figure calculated by MOZARTin JanuaryalongtheTROPOZ flighttrack (top) and measured during 4) is in closeagreementwith the measuredconcentra- II southbound et al. [1996](bottom). tion in the boundarylayer (2.5-3 ppbv north of 40øN) TROPOZ II by Boissard

HAUGLUSTAINE ET AL.' MOZART, MODEL RESULTS AND EVALUATION, 2 MOZARTC5H8 (TROPOZNS FLIGHT)- Jonuory- ppbv •

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sites and for the remote

site of Mauna

Loa Observatory(MLO). Becauseof its short lifetime duringsummer(lessthan a day), C2H4 is not subjectto long-rangetransport, and its mixing ratio is less than 5-10 pptv at MLO. During winter the lifetime is a few

• • 0.05•

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both continental

28,295

ß

days, and a few transport episodeswith mixing ratios reaching occasionally 20-30 pptv are simulated. The model reproducesthe stronggradientsin NMHC mixing ratios observed between polluted and remote locations. The surfacedistribution of the 24-hour averagediso-

prene mixing ratio (2-methyl-l,3-butadiene) is shown -'-

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Figure 6. Observed(circles)andsimulated(boxes)C2H6(ppbv)and 02H4 (pptv) mixingratio (ppbv)seasonal cyclesfor selectedstationsin the northernhemisphere. Measurements are from Solberget al. [1996]for the Europeansitesand from Greenberg et al. [1996]for MaunaLoa Observatory.Boxesgivemean(solidbar), median(dashedbar), 25th, and 75th percentiles.

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HAUGLUSTAINEET AL.' MOZART, MODEL RESULTSAND EVALUATION,2

C5H8 Birkenes (58N,8E) 5.0

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Figure ?. Observed (circles) andsimulated (boxes)CallsandCall6mixingratioseasonal cycles

for selected stations in the northernhemisphere. Measurements arefromSolberg et al. [1996] forthe European sitesandfromGreenberg et al. [1996]for MaunaLoaObservatory. Boxesgive

mean(solidbar), median(dashedbar), 25th, and 75thpercentiles.

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28,298

HAUGLUSTAINE ET AL.: MOZART, MODEL RESULTS AND EVALUATION, 2

CO Mace Head (53N,9W)

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Figure 8. Observed(circles)and calculated(boxes)seasonal cycleof CO mixingratio (ppbv) at selectedstations.Measurements are from Novel.tiet al. [1992,1994]exceptfor Cuiaba[Kirchhoff et al., 1989].Boxesgivemean (solidbar), medilm(dashedbar), 25th, and 75th percentiles.

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HAUGLUSTAINE ET AL.- MOZART,MODELRESULTS ANDEVALUATION, '2x Isoprene - $urfoce - Jonuory

7.ooo

in the CO abundanceassociatedwith transport processes.For example,at the stationsof Mace Head, Niwot Ridge, Tae-ahn, and to a lesserextent, Bermuda,

5.000

the model predicts pollution episodesassociatedwith

3.ooo

specificmeteorological events.Theseeventsare gener-

ppbv 1 o.ooo

1 .ooo o.5oo 0.100

0.050

Cuiaba (Brazil), the high CO mixing ratio (300-500 ppbv) observedfrom July to Novemberis a consequence of biomassburning in this region. The model produces a CO peak approximately 1 month later than obser-

0.005

0.000

ppbv

d ß

-q..

ß

, o

,,

UozA.T

•-•••"•-'---'•

;•

u•;"-';;;;-•;'-' •' ........;•';;'=-'';,ii'6;';i•6 .................................

ally not visible in the measurements,becausethe data are filtered according to wind direction, in order to retain only background levels of CO. At the station of

0.010

0.001

Isoprene - Surfoce - July

28,299

vations

and underestimates

somewhat

the CO concen-

tration during this season. Comparison between model and measurementsis, however, particularly difficult in 10.000 this case, because of the limited spatial resolution of 7.000 the model. At Ascension Island, in the middle of the 5.000 South Atlantic Ocean,the influenceof biomassburning 3.000 is also underestimated by the model. At Cape Grim 1.000 the model overestimatesthe CO mixing ratio by about 0.500 50-60% during summermonths,suggestingthat the in0.100 fluenceof continentalemissionsat this site is too strong 0.050 during winter. O.OLO The monthly mean mixing ratio of CO calculated 0.005 along the track correspondingto the southboundflights o.oo,of TROPOZ II in January 1991 and STRATOZ III o.ooo

Plate 1. Monthly mean 24-hour averagedisoprenesurface mixing ratio calculated by MOZART for January and July conditions(ppbv).

CO- Surfoce - Jonuory

ppbv

....

I"'! 400.

350. 300. o

270.

that biomassburning is most intenseduring the dry sea-

250.

son(Decemberto April in the northerntropicsand July to October in the southerntropics). This seasonalityis

230.

visible in the calculated

surface CO concentration.

200.

170.

Note

also the high concentrationsin northern polar regions during winter associated with carbon monoxide emitted over the continentsand transported to higher latitudes, where photochemical destruction is weak. Over the oceans,in the southernhemisphere,the background CO mixing ratio is generally lower than 70 ppbv. A comparison between the calculated and the observed seasonalvariation of CO surface mixing ratios for 10 selected locations is shown in Figure 8. Model results are presented as monthly means and variability during each month for the last year of model integration. In contrast, measurementsare representedby their monthly mean and their standard deviation over the period of record (up to 10 years). In most cases

the agreementbetweenmodeland observations [Novelli et al., 1992, 1994]is very goodin terms of mean val-

150. 130. 100. 70.

MOZART

M{n = 5.68e+01

CO - Surfoce - July ....

50.

Max = 4.88e+02

ppbv 400.

350. 300.

270. 250.

230. 200. 170.

150. 130.

lOO.

MOZART • 70. ues and amplitude of the seasonalcycle. Most stations ...."""•'A.....•:•'•,;,;i•.................................. 50. exhibit maximum values during winter when CO oxi- •i;,";'%•i'&';i•i dation is smallest. This is particularly visible at high- Plate 2. Distributionof carbonmonoxide(CO) mixing latitude stations, including Point Barrow. The model ratio (ppbv) calculatedat the surfacein January and also provides information on the short-term variability July.

28,300

HAUGLUSTAINE ET AL.: MOZART, MODEL RESULTS AND EVALUATION, 2 MOZART CO(STRATOZ NSFLIGHT)June-ppbv

(a) STRATOZ II

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

LATITUDE

60ø S

40ø

20ø

0

20ø

40ø

80

60ø N

(b) TROPOZ II

MOZART CO(TROPOZ NSFLIGHT) - January - ppbv

I ::•.•i. •:'•

12,' ' '/' ' ,'•::t•'-/..::i::,iiiii:•':i:: ,-':-:':-':,--::-•'-': ::::'-::-.::;:.: i-:--'•L'"" ;-::.'...; '•-•.e•. I 10

10

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:.:.:•.•::.....:?:?:!:::•::ii:•::•B::?:?:•i..i:•if:;•::•.•.::::..:::•i•i::i.:i.i!::•iii:::::•::::::?.::!:.i::i?/i:f:i?::!. :: ::::::::::::::::::::::: •i.t'•:!:.:.•!:. :-::. ..--:;?•-:::::?:;•..:-::.i;i•i•i:-?.i:::::.':.L;?.i:::: :':•:•i• "'•:.•o:::'.:-. :::::::::::::::::::::::::::::::::::::::::::::::::::::: :. ::'•' 1o•:t•iii?iiiiii:'-?-'?:?:?:i!•:. "' 14o • !: '•: !i!!iii..'!i ':•:• i::i .:•:: .:.:: -::•::•::i..::;•i:::%;:.:•i•??•:::•i%::i::;i•:::•::iii;!:•:•!:.•:•::•::•.... &::.. •:'::' ::::::::::::::::::::::::::::::::::::::::::: ..... '.---.:" ::'•:;:•-.. :.i::b---:-:-::.:.. ............... '.' ..-.'.'.:..:.:.'.:.-•f:?i•:•:..•:..• 14o. "::'I•1 0 .::•!•-'..:/:ii!i•:' "::•::L

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30.

-60

-40

-20

0

20

40

60

60øS 40ø

20ø

LATITU DE

0

20ø

40ø

60øN

LATITU DE

Figure 9. CO mixing ratio (ppbv) crosssectionscalculatedby MOZART in July and January alongthe STRATOZ and TROPOZ flight tracks (left), and measuredduring STRATOZ III and TROPOZ II southboundflightsby Marencoet al. [1995](right).

in June 1984 [Marenco et al., 1995; Jonquilresand The MAPS instrument has flown aboard the spaceshutMarenco, 1998] is shown in Figure 9 along with the tle in November 1981, October 1984, and in April and measurements. For the two different seasons,the in-

October

fluence

57øN

of the intense

surface

sources in the northern

hemisphereis visible. A strong seasonalvariation associated with oxidation and mixing processesis found in the northern hemisphere,with mixing ratios at the surface varying from typically 140-180 ppbv in June to 180250 ppbv in January at midlatitudes. The effect of upward transport in the tropics is noticeable during both seasons. The agreement between the MOZART fields

1994.

This

instrument

to 57øS and from

measured

3 to 10 km with

CO

from

a maximum

signal function at about 500 mbar. Plate 3 compares the measured distributions for April and October 1994 with

the

calculated

carbon

monoxide.

Model

results

have been vertically integrated and weighted using the

MAPS averagingkernel[Reichleet al., 1998]. In April

the model reproduces fairly well the interhemispheric gradient of CO with valueslarger than about 100 ppbv and the STRATOZ/TROPOZ observations is generally north of roughly 50øN due to anthropogenicemissions good, especiallyin regionsaffected by industrial emis- and mixing ratios lower than 60 ppbv over the remote sions in the northern hemisphere and biomass burning marine free tropospherein the southern hemisphere. In emissionsin the tropics. The seasonalvariation of the the tropics, localizedmaxima with mixing ratios reachCO abundance in the southern hemisphere seemsto be ing more than 120 ppbv and associated with biomass more pronounced in the observational data than in the burning and biogenic emissionstransported efficently model. from the boundary layer to the pressureof about 500 The NASA MAPS (measurementof air pollution mbar are observedand calculated over South America, from satellites) measurementsprovide the only near- Africa, and southeastern Asia. The model tends to overglobal distribution of carbon monoxide in the tropo- estimate the CO concentrationover Africa. This sugsphere[Reichleet al., 1986,1990; Connorset al., 1996]. geststhat either biomassburning emissionsor CO pro-

HAUGLUSTAINE ET AL.- MOZART, MODEL RESULTS AND EVALUATION, 2

28,301

Table 2. AnnualBudgetof CarbonMonoxidein the Troposphere (Below250 mbar) Calculatedby MOZART, Tg-CO/yr NH

SH

Surface emission

847

372

Photochemicalproduction

539

342

Total source Photochemical

1386 -1092

destruction

Dry deposition

881 2100 -1730

-61

-1221

Burden(TgCO) Lifetime (month)

1219

714 -638

-129

Total sink

Global

-190

-699

196 1.9

-1920

125 2.1

321 2.0

NH, northern hemisphere;SH, southern hemisphere.

duction from isoprene are overestimated in the model during that period or that vertical transport as simulated by the CCM is too vigorous. Another possibility is that the chemical scheme implemented in MOZART overestimatesthe CO yield per oxidized isoprene molecule. Further analysis is required to determine the more likely reason for this disagreement. In

averagedtroposphericburden of CO is 321 Tg (60% located in the northern hemisphere). The calculated global lifetime of CO due to its oxidation and deposition is 2.0 months (2.2 monthswhen only photochemical destructionis considered).The lifetime exhibits a markedseasonalvariation (not shown)and rangesfrom 1.5 monthsduring summerto 2.5 months during winter

October

in the northern hemisphere.

both

the instrument

and the

model

indicate

mixing ratios of 90-120 ppbv in the northern hemisphere. In the southern hemisphere the model tends to underestimate the measured values by about 10-20 ppbv over oceanic regions, in contrast with the model overestimate obtained at the surface at Cape Grim

4. Radicals, Carbonyl

(Figure 8). Strong maxima are visible in the tropics (CO mixing ratio larger than 150 ppbv) due to in-

The primary production of hydroxyl radical OH occurs through the photodissociationof 03 to metastable

tense biomassburning south of the equator. The model does not capture the high concentrations observed in

atomicoxygenO(•D) followedby reactionwith water vapor [Levy,1971]. The very reactivehydroxylradical

October

then attacks most oxidizable speciesand usually leads to the formation of hydroperoxyradical HO2 or organic

1994

over the

Indian

Ocean

and

Australia.

These high concentrationswere not observedduring the

Compounds,

and

Peroxides

November1981 [Reichleet al., 1986]and October1984 peroxy radicals RO2. Plate 4 shows a typical distribution of OH near the [Reichleet al., 1990]flightswhenconcentrations of 4565 ppbv were recorded over the Indian ocean. Unusually high biomass burning activity during the strong 1994

surface calculated from 0000 UT to 1800 UT on July 2. This figure has been chosen to illustrate the caENSO (El Nifio SouthernOscillation)eventis a possible pability of MOZART to simulate the diurnal cycle of wYnlnnntithnœthrthiq disagreementh•t,•7•,• Mth7.ART short-lived speci.o• Aq oYn•ct•d the (•14 cn,•centration and MAPS.

The global and hemisphericcarbon monoxide burden

is higherthan 1 x 106molecules cm-3 duringdaytime in the tropics and at midlatitudes and, generally, in the

cm-3 duringnighttimeover and budget in the troposphere(below 250 mbar), as range103-104molecules the continents. One should note, however,that during nighttime the surface OH density reachesvalues higher

derived by the model, are summarized in Table 2. Surface primary emissionsconstitute 58% of the total CO sourceon the global scale,while the photochemicalproduction associatedwith the degradationof methane and NMHCs accounts for the remainder. Approximately 70% of the CO surface emissionand 60% of its photochemical production take place in the northern hemi-

than 1 x 105molecules cm-3 in regionswherebiogenic

hydrocarbonemissionsare high (e.g., tropical forest in Africa). These values, associatedwith production of OH and peroxy radicals in the nocturnal stable layer by reaction of volatile organic compoundswith 03 and sphere.A large fraction (63%) of the CO oxidationby NO3 are consistentwith the results obtained by Platt et OH occurs in the northern hemisphere. Dry deposi- al. [1990]and Bey et al. [1997].MaximumOH concencm-3) are calculated tion contributesto about 10% of the global sink (two trations(10-18 x 106molecules thirds being deposited over continents in the northern in regionsof high NOx concentrations(i.e., North Amhemisphere).The apparent imbalancein the CO bud- fica, Europe, China). High OH concentrationsare also get (180 Tg/yr, or 9% of the total source) is associ- predicted in regionsof elevated surfacealbedo and high ated with transport to the stratosphere. The annually insolation(e.g., Sahara) whichfavor high 03 photolysis

28,302

HAUGLUSTAINE ET AL.' MOZART, MODEL RESULTS AND EVALUATION, 2

OH - Zonal Mean - January - le5 cm-3

Figure 11 showsthe zonally averagedHO2/OH concentrationratio calculatedfor July (monthlymean values). At the equator this ratio decreasesfrom about

20 t.

100 at the surfaceto approximately 5 at 15 km altitude. At high latitudes in the summer hemisphere,where the abundanceof NOx and ozoneare low, the calculated ratio reaches300 in the lower troposphere. As illustrated

in this figure, in the lower troposphere(below about 5 km), HOx is mainly composedof HO2. In the upper troposphere,CO (and hydrocarbons)is lessabundant, while 03 and NO are more abundant than in the lower

troposphere. Consequently,in this region the recycling

of HO2 to OH is muchfaster and the HO2/OH ratio is lower than near the surface. -5O

0 LATITUDE

5O

The distribution of the daytime averaged total per-

oxy radicalmixingratio PO2 (= HO2 q- •-•i RO2,i, whereEi RO2,iis the sumof all organicperoxyradicalsconsidered in MOZART) calculatedat the surface

OH - Zonal Mean - July - le5 cm-3

and at 200 mbar is shown in Plate 5 for July conditions. Because of their short lifetime, peroxy radicals exhibit maximum values in the continental planetary boundary layer near polluted regions. At the surface, the mixing ratio reaches 100-300 pptv over the eastern United

States and about

100-200

over central

Eu-

rope and China. High concentrations(reaching100150 pptv) are alsofoundin biomassburningregionsor wherebiogenicemissions of hydrocarbons are high (e.g., southernAmerica,Africa, Indonesia). Over the ocean, the calculated PO2 mixing ratio is generally within the 10-30 pptv range. These mixing ratios are generally consistentwith existing measurements. During -50

0

50

LATITUDE

ROSE (Rural Oxidantsin the SouthernEnvironment), Canttell et al. [1993]measuredmixingratiosreaching 100-300 pptv in the southeasternUnited States. Mihel-

Figure 10. Zonally averagedOH density (105 cic et al. [1997]reportedmixingratiosof 40-60 pptv in molecules cm-3) crosssectioncalculatedfor January Germanyduringmoderatelypolluted conditions(NO•

and July conditions. Dashed line indicates model _ 60[ ...........

{3.

• 40

,-, 50

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03 Bermuda(32N,64W)

03 Niwot Ridge (40N, lO5W) .

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03 South Pole (89S,24W)

03 Cape Grim (40S,144E)

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03 Cuiobo(16S,56W)

03 Samoa (14S,170W) 3 30

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Figure 21. Observed(circles)and calculated(boxes)seasonalcycleof 03 mixingratio (ppbv) at selectedstations.Measurements are from Oltmansand Levy [1994]exceptfor Cuiaba [Kirchhoff et al., 1989].Boxesgivemean (solidbar), median(dashedbar), 25th, and 75th percentiles.

ß

D

28,322

HAUGLUSTAINEET AL.: MOZART,MODELRESULTSAND EVALUATION,2

tion are intense), with the highest valuesbeing found over the ocean where surface dry deposition of O3 is weakest. Becausethe ozonelifetime is longestin winter, ozone transport acrossthe ocean is strong and is visi-

from the stratosphere. The model also underestimates

the concentrations during winter at Cape Grim as well

as the September maximum at Cuiaba associatedwith biomassburning emissions. ble over the North Atlantic and North Pacific in JanThe zonallyaveragedozonemixing ratio calculated uary During January, a sharp interhemisphericdiffer- in Januaryand July is shownin Figure 22. Valuesin ence is visible near the equator with low-ozone concen- the lowertroposphere (2-5 km altitude) are typically trationsin the southernhemisphereoverthe oceans(_< 10-30 ppbv and 20-50 ppbv in the southern and north-

10-15 ppbv). The minimum surfaceozoneconcentra- ern hemispheres, respectively. Theselow mixingratios in Amazonia and Africa are the result of aretransportedupwardin the tropicsand valuesof typdry depositionover the tropical forest and chemicalde- ically20-40ppbvare foundat 10-15 km nearthe equastruction of OH and O3 by isopreneand its degradation tor. Stratosphericozone concentrationsof more than products(in theseregions,isoprenereaches4-10 ppbv 250 ppbv are predicted by the model above 10 km at in January;seePlate 1). Similar resultshave been ob- highlatitudes.The highesttropospheric mixingratios tainedby Houwelinget al. [1998]overthe tropicalrain are calculated at midlatitudes in the northern hemiforest. This is also in agreement with the low ozone spherewhereintrusionfrom the stratosphereand in situ mixing ratios (6 ppbv during daytime) measuredover photochemicalproductionare important. The 100-200 the Amazon forest during the ABLE 2B field expedition ppbvisomixingratio lines(representative of tropopause [Jacoband Wofsy,1990]. values)arelocatedat about17km in the vicinityof the tions simulated

The seasonalcyclesof surfaceO3 mixing ratios calculated and observed at selected locations are compared in Figure 21. Model results are presented as monthly means and variability during each month for the last year of model integration. In contrast, the measurements correspondto monthly mean values and standard

over the period of record (up to 10 years). Observed mixingratios are taken from the CMDL network[Oltmans and Levy, 1994], except in the caseof Cuiaba [Kirchhoffet al., 1989]. The modelzeproduces the ob- •

03 - Zonal Mean - January- ppbv

i/'-" •-o: øø••

•o-

10

served mixing ratios and their seasonalcycle in many

cases,especiallyfor low- and mid-latitudestations(e.g., Mace Head, Bermuda,Barbados,Samoa). As discussed by Hauglustaineet al. [1998b],MOZART reproduces the observed seasonal cycle of ozone in the northern

Atlantic Ocean. At Bermuda a strong seasonalcycle is observedand simulated. At this station, high O3 mixing ratios are obtained during spring,reaching50 ppbv on averagein April. During summerthe meteorological patterns of the North Atlantic Ocean are dominated by the Bermuda-Azoreshigh-pressuresystem, and the

-50

0 LATITUDE

50

03 - Zonal Mean - July - ppbv

Bermuda site is under marine influence. Low O3 concentrations of about 20 ppbv are simulated and mea-

sured during July-August at this station. A similar but less pronounced pattern is obtained at Barbados. Over the northern Pacific, at Mauna Loa, the observed spring maximum, probably associated with transport

of ozone from higher latitudes, is somewhat underestimated in the model. At Niwot Ridge, Colorado, the

modelproducesa summertimemaximum(causedby enhancedphotochemicalproduction) which is more pronounced than in the data, suggestingthat the model overestimatesthe influenceof pollution at this high altitude (site elevation3000 m). The valuescalculated at high latitudes, for example at Barrow and at the -50 0 50 LATITUDE South Pole, are generally lower than the observedvalues. This discrepancy is attributed to a combination of Figure 22. ZonallyaveragedO3 mixingratio (ppbv) ververyy low NOx concentrationsin remote regions at crosssectionscalculatedfor January and July condihigh latitudes and an underestimate of ozone transport tions. Dashed line indicatesmodel tropopause.

HAUGLUSTAINE ET AL.' MOZART, MODEL RESULTS AND EVALUATION, 2 Alert (82N,62W) - 800tabor ß

Alert (82N,62W) -! 300tabor ! i i ! i i i !

Alert (82N,62W) - 500tabor

,

!

300

i

i

!

i

!

!

!

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DATA

• 80 • • I•MOZART :•

40

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500

• 200

60

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600

250

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28,323

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i

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i

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•

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0

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(• 60 •

;

'

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(• 60 o

M

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Resolute (75N,95W) - 50Orebar

'øø f ........... -• 40 •

i

t

,

F

M

A

M

J

J

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Resolute (75N,95W) - 300mbor

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Edmonton(53N,114W) - 500tabor

Edmonton(53N,114W)- 800tabor 100

F

..........

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F

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Edmonton(53N,114W) - 300tabor 300

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80

80

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F

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A

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,! A

M

J

J

A

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N

D

Figure 23. Measured (circles) andcalculated (day-to-day, solidline;monthlymean,stars)

seasonal cycleof 03 mixingratio(ppbv)at 12stationsandat 800,500,and300mb. Observations arefromozonesoundings compiled by J. Logan(personal communication, 1996).

equatorand9-11 km near50ø with differences in height stations of the northern hemisphere but is underestiof less than I km between summer and winter.

mated by 10-15 ppbv in the southern hemisphere and

t the Figure23 showstho qon..qnnnl ovoh!ti_on nff,ho nznne a,t hi•her ]a,tit•]des in the northern hemi,qnhere. mixingratio calculatedand observed at threedifferent Japanesestation of Naha, a seasonalminimum in ozone pressure heights(800,500,and300 mbar)for 12 differ- is observedduring June-Augustand is captured by the

entstations(J. Logan,personal communication, 1996).

model. This 03 minimum is associated with the mon-

sooncirculation which brings air of marine and tropical origin to the site. In the midtroposphere the model tion with, however,somespecificexceptions.The tim- has a tendency to somewhat underestimate the ozone ing of the ozonemaximumin pollutedregions(spring concentration. Except in a few cases where transport in the upper troposphereand a gradual shift toward from the stratosphere seems to be underestimated in

The model usuallyreproducesthe absolutevalue and

the seasonal variation of the observed ozone concentra-

the summerseasonas the altitude decreases)is gener- the presentversionof MOZART (e.g., Resolute,Walally well simulatedby MOZART for midlatitudesta- lops, Aspendale/Laverton),the model reproducesthe tions(e.g.,Sapporo,Payerne,Boulder).Near the sur- ozone behavior in the vicinity of the tropopause. In this regionthe ozonevariability producedby the model face the seasonal evolution of the ozone mixing ratio is well reproducedat the middle and low latitude is lower than the observations.At high altitudes (e.g.,

28,324

HAUGLUSTAINEET AL.' MOZART, MODEL RESULTSAND EVALUATION,2 Payerne (47N,7E) - 800mbar

Payerne (47N,7E) - 500mbar

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Sopporo(43N,141E) - 500mbar

Sopporo(43N,141E) - 30Orebar

Sopporo(43N,141E) - 800mbor

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M

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D

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Boulder(40N,105W) - 500tabor

.

A

M

J

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;300 1........... 250

150

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60

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Figure 23. (continued)

Alert, Resolute)the modelshowsthe occurrence of brief episodesduring which intrusionsof stratosphericair causestrong enhancements in the ozonemixing ratio of 300-600ppbv at 300 mbar. It is importantto note that no constraintis applied to ozonein the model below 60 mbar (or about 20-25 km) and that above250 mbar the vertical resolution of the model has been en-

compares themeasured 03 duringJanuary-March 1995 at 11-12 km and 8-10 km providedby MOZAIC and the distributions calculated by MOZART undersimilar conditions.The modelreproduces the observed vertical

andmeridional gradients in ozone.At 11-12km,mixing ratioshigherthan 200ppbvaremeasuredandcalcu-

latednorthof40ø-50øN andvalues in therange30--60

hancedby a factorof 2 in comparison with the standard ppbvaregenerally obtained overthetropicalandSouth

CCM [Brasseur et al., thisissue].

AtlanticøOverAfricathe modelunderestimates the O3 measurements collectedin 1995by about 10-20 ppbv. service aircraft) project provides the distribution of At the altitude rangeof 8-10 km the calculatedozone ozonein the uppertroposphere and lowerstratosphere mixingratioreaches 100-200ppbvat highnorthernlatfrom routine measurements on five commercial aircraft itudes,generallyin agreementwith the MOZAIC disoperatingintercontinental flights[$hureet al., 1997;A. tribution.However,mixingratiosof morethan200-300 Marencoet al., personal communication, 1997].A de- ppbv,observed overthe northernAtlantic,are not reThe MOZAIC (measurement of ozoneby airbusin-

tailed comparisonbetween MOZAIC and severalCTMs

produced by the model.The modeloverestimates by (including MOZART)will be presented elsewhere [K. about 10-15 ppbv the ozoneminimum observedat this

Law et al., manuscript in preparation,1998). Plate 13 altitude in the tropical Atlantic. It shouldbe noted

HAUGLUSTAINE ET AL.' MOZART, MODEL RESULTS AND EVALUATION, 2 Wollops(58N,76W)- 800mbor

2oo• t ,, ß......... O DATA

Wollops(58N,76W)- 500mbor

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Figure 23. (continued)

that very low ozonemixingratios (03 •_ 30 ppbv) are ical cyclingwithin the family. However,since03 is calculated in the rising branch of the Walker circula- the most abundant component of Ox in most of the tion over the tropical Pacific Ocean. In this region, troposphere,the Ox and O3 budgetscan be viewedas

air masses with lowozonemixingratiosare efficiently equivalent.Photochemical production of O• (Pox) is transportedupwardfrom the marineboundarylayerto

mainly due to the reactionof hydroperoxyor organic

the upper troposphere. The location of this ozone min-

peroxy radicals with NO to form NO2 which is further

imumin the uppertroposphere is consistent with the ozonesoundings reportedby Kley et al. [1996]for the CEPEX campaign•the lidar measurements obtained duringPEM-WestA andB [Wu et al., 1997]., andwith

photolyzed duringdaytimeto form O(3p) and subsequentlyozone. Photochemical lossof O• (Lox) is principallyattributedto ozonephotolysis followedby the reactionof 0(1D) with watervapor,to reaction

the measurements collectedduringTOTE/VOTE (A.

of ozonewith OH and HO2, and to reactionof ozone

JoWeinheimeret al.• personalcommunication•1997).

with NMHCs. Plate 14 showsthe calculatednet O•

Thebudgetofozone in thetroposphere isgoverned by intrusion fromthe stratospheric reservoir, in situphotochemical production anddestruction, anddry depositionat the surface.The following budgetanalysis is for odd oxygenO• definedas the sumO3 4- O(1D) + O(3P) + OH + HO2+ NO• + 2xNO3+ 3xN•O5 + 2xHNO3 + 2xHNO4 + PAN to account for chem-

photochemical production rate (Pox - Lox) averaged overtheboundary layerheight(lowestfivelevelsin the modelor about2 km altitude),andin the freetroposphere(up to the levelof 250 mbar)for Januaryand July conditions.DuringJuly, whenthe photochemicalactivityis intense, thenet production rate reaches maximum valuesof20-40ppbv/din theboundary layer

28,326

HAUGLUSTAINE ET AL.- MOZART, MODEL RESULTS AND EVALUATION, 2 Somoo(14S,170W) - 800tabor

i

loo

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Figure 23. (continued)

over the eastern United States, western and central Eu-

rope, and 10-20 ppbv/day over easternChina, where anthropogenicemissionsof NOx and hydrocarbonsare high. During January the Ox production rate over these regionsremainspositive(1-3 ppbv/d), althoughconsiderably smaller than in July. The maximum values are also somewhat displaced toward the south where the photolytic radiation is more intense. In particular, during wintertime, the maximum Ox production rate over the United States is shifted toward the southeast,where isopreneemissionsremain significant,providingthe peroxy radicals used to fuel the Ox photochemical produc-

is generallynegative (net lossof ozone) exceptwithin continental air plumes emanating from North America and Asia during January and South America, South Africa, and Australia during July. This feature is most prominent during winter time when the lifetime of ozone precursorsis longest. As discussedby Hauglustaine et

al. [1998b],ozoneis exportedfrom the pollutedcontinental boundary layer to the marine atmosphere which acts as a photochemical sink for ozone. It is interesting to note that in spite of the limited amount of NO•

available(10-20 pptv) at high latitudes the model predicts a small positive photochemical O• production in

tion. Other maximum valuesreaching5-10 ppbv/day polar regionsduring summertime. This is explained by (althougha factor of 2-3 smallerthan those reported the small destruction rates of ozonein this relatively dry in industrializedregionsduring summertime)are found environment, enhancedphotolytic radiation over the ice over the African

and South

American

continents

and

are a consequenceof biomass burning emissions. In the marine boundary layer the net Ox production rate

sheet, and longer lifetime of NO•. This production rate

remains,however,very low (1 ppbv/d) dueto the small amountsof precursorspresentin this region. In the free

HAUGLUSTAINE ET AL.: MOZART, MODEL RESULTSAND EVALUATION, 2 MOZAIC 05, Jon-Feb-Mor o..;

.........

; .........

95, 11-12km

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

,..........

; .........

MOZAIC05, Jon-Feb-Mor

ppbv ; .........

28,327

95, 8-10km

ppbv

; ..........

700.

700.

500.

500.

500.

500.

200.

200.

100.

100. 90.

90.

..........i.........;.

80.

'..............

:• .-:......

80.

70.

70.

60.

50.

40.

40.

30.

30.

20.

20. .............................................................

O. Min = 2.00e+01

05, Jon-Feb-Mor,

Min = 1.õOe+01

Mox = 5.65e+02

11 - 12krn

60.

.

50.

0.3, Jori-Feb-Mot,

ppbv

:,',r

..........

r--

'

0

Mox -- 4.2õe+02

8-10kin

ppbv

700.

7O0.

500.

500.

300.

300.

200.

200.

--•100.

100.

90,

90.

80.

80.

70.

70. 60.

60.

50. 40.

ß

30.

50. 20.

Min = 2.09e+01

Mox = 1.49e+05

O.

20.

MOZART

O.

Min = 2.00e+01

Mox = 5.29e+02

Plate 13. Ozonemixingratio(ppbv)measured duringthe MOZAIC program(A. Marenco et al.,personal communication, 1996)in January-March 1995forthe11-12kmand8-10kmaltitude

ranges (top),andozone distributions simulated byMOZARTundersimilar conditions (botto•n).

tropospherea smallernet Ox productionrate is gener- react with ozone. At higher latitudes the O• lifetime ally calculateddue to both smallerproduction(lower increasesto 2-4 months in the summer hemisphere and hydrocarbonand NOx concentrationsin the free tro- to more than i year in the winter hemispheredue to posphere)and destruction(decreasing water vaporand absenceof photochemicallosses.In the boundary layer radical concentrationswith altitude) terms. A maxi- the effective O x lifetime will be even shorter when dry mumnet photochemical productionrate of 5-10 ppbv/d depositionat the surfaceis considered.Interestingly, is predictedoverthe continentsin the tropicswherecon- over polluted regions,an elevated ozone photochemivectionefficientlytransportsozoneprecursorsout of the cal productionis calculatedbut the export of ozoneto boundarylayer. A strongseasonalcycleof the O• pro- the remote troposphereis limited by its short lifetime. duction rate related to the occurrence of convection is In the free troposphere,longer lifetimes are predicted, obtained. In contrast with the boundary layer, due to rangingfrom 1-3 monthsin the tropicsto more than the rapid decreasein water vapor abundancewith al- I year in polar regions. The ozonelifetime exhibits a titude, a net production rate (generally lower than 1 strongseasonalcycleand rangesat midlatitudesfrom ppbv/d) is calculatedin the freetroposphereand, more 50-100daysduringwinterin the boundarylayer(when importantly,in the uppertroposphere(not shown)over the photochemicalactivity is low) to only 10-20 daysin July. Similarly,at midlatitudesin the free troposphere, oceanic regions. The correspondingO• photochemicallifetime in the it rangesfrom 300-500 days in winter to 80-100 days boundary layer and in free troposphere(defined as in summer. Table 3 providesan estimate of the global and hemiO•/Lo•) isillustrated in Plate15forJanuaryandJuly.

Shortlifetimes(lessthan 10 days)are predictedin the sphericbudgetsof ozonebelow the pressurelevel of boundarylayer of the tropicalregionswherethe pho- 250 mbar (about 10 km) as calculatedby MOZART, tochemicalsinks of ozone are high (high water vapor and Figure 24 showsthe seasonalcycleof the various and radicalconcentrations).Lifetimesshorterthan 5 ozonebudget components. The ozonephotochemidaysare calculatedin regionswherehigh isoprenemix- cal productionis 3018Tg/yr in globalaverage(67% of ingratio(i.e.,tropicalforest,southeast UnitedStates) the productionin the northernhemisphere). Strato-

28,$28

HAUGLUSTAINE ET AL.:MOZART, MODELRESULTS ANDEVALUATION, 2

Ox Net Production,January,BoundaryLayer

ppbv/day '

ß

ßß

MOZ,•RT ' Min= -2•88e+00'Max"2.14e•01 Ox Net Production,January, Free Troposphere

I•

•,,•'•, • 4.0 3.0

'..

'

I.

40.0

10.0 5.0 "

'..

ppbvlday

25.0 20.0 15.0

:

t

Ox Net Production, July, BoundaryLayer

40.0 35.0 30.0

2.0 1.0

0.0 -1.0 -2.0 -3.0

ppbv/day

-

MOZART

Min=-2.•2e+00' Max'=' '3.74'e•.01'

'

Ox Net Production, July,Free Troposphere

ß•

35.0 30.0 25.0

20.0

15.0 10.0 5.0 4.0 3.0 2.0 - 1.0 0.0 -1.0 -2.0

-3.o

ppbv/day 9.0

9.0 7,0 5.0 3.0 2.5 2.0 1.5 1.0

7.0

5.0 3.0 2.5 2.0

1.5 1.0

0.6

0.8 0.4

0.2 0.0 -0.2 MOZART

Min=-6.:76e-01 ' Max'7.43e+•)0

'

-0.4 -0.6

MOZART

H0.8 0.6 0.4 0.2 0.0 -0.2 -0.4

Min=-7.•11e-01 ' Max=1.01e+"01

Plate 14. Ox photochemical net production (production-loss)calculated for January(left) andJuly(right)conditions by MOZART(ppbv/d).Distributions in the toppanelareaveraged overthe boundarylayerheight,andoverthe freetroposphere for the bottompanel.

sphericintrusion(391 Tg/yr) contributesfor 11% to June. Since the destructionpeaks simultaneously,the the globalsourceof ozonein the troposphere(contri- net productionexhibitsa maximumshiftedby about butions of 8% and 18% in the northern and southern I monthand occurringin May. In the southernhemiexhibit hemispheres, respectively).The photochemical destruc- sphereboth the productionandthe destruction tion is 2511Tg/yr in globalmean(61% in the northern maximum valuesin October-February.From December hemisphere). Dry deposition at the surface(898Tg/yr) to March, a net O• photochemicallossis predictedin contributesfor 26 % to the global sink of tropospheric the southern hemisphere. The influx from the strato-

ozone(about30 % and 20 % in the northernandsouthern hemisphere,respectively).It is clear from theseresultsthat the budgetof tropospheric ozoneis dominated by photochemistry.The net photochemical production (production-destruction)is the difference betweentwo largeterms.Integratedoverthe wholetroposphere domain, the net productionis 507 Tg/yr (95% in the northernhemisphere).Of this 507Tg, about228Tg (•

45 %) is produced in the boundarylayer(fivelowerlev-

sphereacrossthe 250 mbar upperboundaryexhibits strongseasonal variabilityand an annualmaximumin March-April of 1200 Tg/yr The dry depositionalso showsa strong seasonalcycle in the northern hemisphereassociated with largervegetationuptakeduring summer.The globaltropospheric burdenof 03 in the modelis 194Tg. Approximately60% of this burdenis found in the northern hemisphere.The photochemical lifetime of ozone as calculated in MOZART

is about 1

elsof the modelor belowabout 2 km altitude), with the monthin globaland annualaverage.When surfacedry the globallifetimedecreases to remainingbeingproducedin the free troposphere.The depositionis considered, about 20 days. As shown in Figure 24 and illustrated in net productionexhibitsa strongseasonalcycle(Figure Plate 15, this lifetime exhibits a strong seasonal and ge23) and is mainlydominatedby the enhanced photovariability.In the northernhemisphere the chemicalproductionoccurringduring summerin the ographical northernhemisphere.The globalnet productionranges lifetimesrangefrom 15 days in summerto about 30

from about200 Tg/yr in Januaryto 600-700Tg/yr in days in winter on average. The globalozonebudgetin MOZART can be comJune-September.In the northernhemisphere the maxpared to previousestimates givenby variousCTMs imum photochemical productionoccursat the end of

HAUGLUSTAINE ET AL- MOZART, MODEL RESULTS AND EVALUATION, 2 Ox Lifetime. Jonuory, BoundoryLoyer

28,329

Ox Lifetime, duly, BoundaryLoyer

Days

Ooys 500.

J•500. 200.

200.

100.

100.

50.

50. 30.

30.

20.

20.

ß

.

,

15.

15.

13.

13. 10.

10.

9.

,,

g.

ß

8.

8.

7.

7.

5. 4.

laln = 4.72e+00

Mox = 3.39e+03

Ox L;fetlme, January, Free Troposphere

! MOZA. RT Min -- 4.85e+00

i

i

?

i

:

.

i

:

ß

:

6.

:

5.

1

4.

Mox -- 2.43e+04

Ox Lifetime, duly, Free Troposphere

Doys

:

1ooo.

Ooys 1000.

500.

500.

300.

500.

2OO.

200.

150.

150.

lOO.

100.

90.

90.

80.

80.

70.

70.

60.

60.

50.

50.

40.

40.

30. 20.

MOZART

10.

Min = 2.25e+01

Mox = 9.72e+04

Plate 15. Ox photochemical lifetimecalculated for January(left) andJuly (right)conditions byMOZART(days).Distributions in thetoppa. nelareaveraged overtheboundary layerheight, and overthe free tropospherefor the bottom panel.

ble4). Theresults differquitesignificantly among the

tion lower than in previous studies. Consequently,the

the definition of the domain under consideration.The

model values. A significantspread among the models

models, depending on modelassumptions aswellason calculatednet production is on the high side of previous

globaltropospheric photochemical production ranges has also been obtained in terms of ozone influx from the from3200Tg/yr in theworkof Roelofs andLelieveldstratosphere.This term rangesfrom 400 Tg/yr in the

[1995] (onlymethane chemistry) to4550Tg/yearinthe work of Wanget al. [1998]to 846 Tg/yr in the work of work of Milllet and Brasseur[1995](their modeldo- Bernstenand Isaksen[1997]. Tie and Hess[1997]have mainincludesthe lowerstratosphere). The photochem- calculated a stratospheric flux of ozone to the tropoversion ical destruction rangesfrom 3037Tg/yr [Roelofs and sphereof 792Tg/yr with the middleatmosphere Lelieveld,1995]to 4000Tg/yr [Milllet and Brasseur,of the NCAR CCM (MACCM2). The stratosphericin1995].Theproduction calculated withMOZARTis in trusion calculatedwith MOZART (391 Tg/yr) is gentherangeof previous modelestimates andthedestruc-erally on the low side of previousestimates. Future Table 3. AnnualBudgetof Ozonein the Troposphere (Below250mbar)Calculatedby MOZART, Tg-Oa/yr NH

Photochemicalproduction Stratospheric influx Total source Photochemical destruction

Dry deposition Total sink

Burden(Tg) Lifetime(days)

2023 170 2193 -1540

-625 -2165

114 19

SH

995 221 1216 -971

-273 -1244

79 23

Global

3018 391 3409 -2511

-898 -3409

193 21

28,330

HAUGLUSTAINE ET AL.- MOZART,MODELRESULTSAND EVALUATION, 2 MOZART Ox Destruction

MOZART Ox Production i

4OOO

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L i

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iiiIiiiiiiI

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MOZART Ox Lifetkne

MOZART Ox Flux 1500 .

,,*,,'

',

/, •.

IOO0

,,,

I J

I F

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*

II A

I M

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Figure24. Seasonal variation ofintegrated ozone photochemical production, destruction, and netproduction (Tg/yr),surface drydeposition (Tg/yr),stratospheric influx(Tg/yr),andphotochemical lifetime (days) calculated bythemodel. Thenorthern hemisphere values arerepresented bythedashed line,southern hemisphere isthedotted line,andthesolid lineistheglobal integral. versionsof MOZART will be developedto investigate focusingmainly onozoneandits precursors.The results is able to simulate the distribufurther the distribution and budget of ozonein the up- show that MOZART tions of speciesin the tropospherewith fair agreement. per troposphere. MOZART reproducesaccurately important transportchemistry processes,including the ventilation of the 7. Conclusion

A new global three-dimensionalchemicaltransport model, called MOZART, which includesa comprehensive descriptionof troposphericchemistry,has been developed.We havepresenteda detailedevaluationof the model resultsand comparisonswith observationaldata,

planetaryboundarylayer, convectivetransportand the Walker circulationin the tropics,the impact of the monsoon circulation on chemical tracers, and the vertical and seasonalgradientsof ozoneand nitrogen speciesin the vicinity of the tropopause.

The seasonalcycle and geographicaldistribution of

HAUGLUSTAINE ET AL.: MOZART, MODEL RESULTS AND EVALUATION, 2

28,331

Table 4. Annualand GlobalBudgetof Tropospheric OzoneCalculatedby VariousCTMs, Tg-O3/yr Photochemistry

Production

Milllet and Brasseur[1995] Lelieveldand van Dotland [1995] Roelofsand Lelieveld[1995] Levy et al. [1997] Bernstenand Isaksen[1997] Roelofset al. [1997] Wanget al. [1998] This

work

Influx

Destruction

4550 3609 3206 ...... ......

-4000 -3183 -3037

3415 4300 3018

-3340 -3810 -2511

Net 550 426 169

model reproduces the wintertime maximum in CO and

Deposition

Net

-1100 -953 -740 -825 -1178

-550 -425 -165

295

550 528 575 696 846

75 490 507

459 400 391

-534 -890 -898

-75 -490 -507

128

methane, NMHCs, and carbon monoxide are generally well simulated by the model. In particular, the

Stratosphere

-129 -332

PEM-West B and PEM-Tropics A. The model overestimates HNOa by a factor of 2-3 over North America and in biomassburning regions.This feature emphasizesse-

NMHCs whichhasbeen observedat high latitudes, and the strong gradients in NMHC mixing ratios existing between polluted regions and remote locations. The model would benefit from a better representation of NMHC biogenicemissions(specificallyisoprene)over

vereshortcomings in our understandingof the nitrogen

the continents

tration

and oceanic

emissions of NMHCs

and

CO which are subject to large uncertainties.Similarly, the role played by biomassburning emissionsin the

budget in the iYeetroposphereand more attention will

be devotedto this questionin forthcomingstudieswith MOZART.

MOZART generally reproducesthe absoluteconcenand the seasonal variation

of measured ozone

in the free troposphere. The observed transition from an ozone maximum in spring at remote locations in the

tropics on the distribution of CO should be addressed

freetroposphere to a summermaximumin regionscon-

more precisely. The global mean OH concentrationis probably underestimated by 10 % in the model. The

trolled by photochemicalproduction in the lower troposphereis generally well reproducedby MOZART. At higher latitudes the model tends to underestimate the ozone concentrationthroughout the troposphere. This discrepancy has been attributed to insufiqcientintrusion of ozone from the stratospherein the model. The globally averagedstratosphericinflux calculatedin

distributionsof radicals(OH, RO2, HO2/RO2) are generally consistent with available measurements. Recent

work has stressedthe important role played by aldehydes, peroxides, and acetone as potential sourcesof

radicalsin the upper troposphere[Singhet al., 1995; Jaegldet al., 1997;Prather and Jacob,1997]. MOZART showsgenerally good agreementfor these specieswith observedmixing ratios. In particular, the model reproduces reasonably well the distribution of acetone in the free troposphere. The model evaluation in the tropics suggeststhat the biomassburning source of these

MOZART (391 Tg/yr) lies on the low sideof previous estimates. The calculatednet photochemicalproduction of ozoneis the difference betweena largegrossphotochemicalproduction(7-8 timeslargerthat the stratosphericinflux) and a largegrossdestruction(2-3 times largerthat the surfacedry deposition).In the boundary

species(e.g., CH20, H202) might be underestimated layer a large net ozoneproduction is calculatedover the continents. However, the short ozone lifetime limits the impact of that production on remote locations. Over The globalbudgetof nitrogenspeciesin the tropo-

in current

emission inventories.

sphereis an important area for future model improve- the oceans a net destruction is calculated in the boundments. MOZART generally reproducesthe observed ary layer, confirmingthat the marine atmosphereacts concentrations of nitric oxide but tends to underestias a chemicalsink for ozone. In the free troposphere mate PAN over continentalregionsin the free tropo- a small net ozone production rate is calculated on the sphere. Previous models overestimated nitric acid and global scale. However,in this regionthe ozonelifetime

HNO3/NOx ratiosin the remotetroposphere [Jaffeet is longer and the accumulation of ozone could be imal., 1997;Thakuret al., 1998;Wanget al., 1998],and I)ortant in terms of global burden. mechanisms not accounted for in the models have been

Although many of the results provided by MOZART

proposed to solvethis discrepancy [Chatfield,1994;Fan are encouraging,the model will continouslyrequire imet al., 1994;Hauglustaine et al., 1996].HNO3isalsosig- proved formulations and parameterizations of physical nificantly overestimated in MOZART over the Pacific during summer in comparisonwith measurementsre-

and photochemicalprocesses.The availability in the future of quasi-globalobservedfieldsprovidedby planned portedduringPEM-WestA. No evidenceis found,how- spaceand airborne projects will be of considerablehelp

ever,for a systematic overestimate by the modelduring

to evaluate

future

versions of this model.

28,332

HAUGLUSTAINE ET AL.: MOZART, MODEL RESULTS AND EVALUATION, 2

Acknowledgments. We thank P. Hess, B. Ridley, and L. Horowitz for their valuable comments on this manuscript. We gratefully acknowledgeA. Marenco and the MOZAIC team, and J. Logan for providing their data prior to publication.

All

GTE

data

were

obtained

from

the

GTE

Data Archive ftp site (http://www-gte.larc.nasa.govand ftp-gte.larc.nasa.gov)oThis work has been supportedin part by the National Aeronautics and Space Administration

(NASA) undercontracts2529-MD/BGA-0017 and AEAP95-014. The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under the sponsorship of the National Science Foundationo

comparisonof data and models, Atmos. Environ., 31, 1851-1904, 1997.

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(Received February20, 1998;revisedJuly7, 1998; acceptedJuly 9, 1998.)