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Chamber Simulation of Photooxidation of Dimethyl Sulfide and Isoprene in the Presence of NOx
http://www.atmos-chem-phys-discuss.net/12/14669/2012/acpd-12-14669-2012.html ( Publisher's URL )
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Title: Chamber Simulation of Photooxidation of Dimethyl Sulfide and Isoprene in the Presence of NOx
Series Title: Atmos. Chem. Phys., 12, 1–13, 2012
Physical Description: Journal Article
Creator: Chen, Tianyi
Jang, Myoseon
Publisher: Copernicus Publication
Place of Publication: online
Publication Date: June 8, 2012
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Abstract: To improve the model prediction for the formation of H2SO4 and methanesulfonic acid (MSA), aerosol-phase reactions of gaseous dimethyl sulfide (DMS) oxidation products (e.g., dimethyl sulfoxide (DMSO)) in aerosol have been included in the DMS kinetic model with the recently reported gas phase reactions and their rate constants. To determine the rate constants of aerosol-phase reactions of both DMSO and its major gaseous products e.g., dimethyl sulfone (DMSO2) and methanesulfinic acid (MSIA), DMSO was photooxidized in the presence of NOx using a 2m3 Teflon film chamber. The rate constants tested in the DMSO kinetic mechanisms were then incorporated into the DMS photooxidation mechanism. The model simulation using the newly constructed DMS oxidation mechanims was compared to chamber data obtained from the phototoxiation of DMS in the presence of NOx. Within 120-minute simulation, the predicted concentrations of MSA increase by 200~400% and those of H2SO4, by 50~200% due to aerosol-phase chemistry. This was well substantiated with experimental data. To study the effect of coexisting volatile organic compounds, the photooxidation of DMS in the presence of isoprene and NOx has been simulated using the newly constructed DMS kinetic model integrated with the Master Chemical Mechanism (MCM) for isoprene oxidation, and compared to chamber data. With the high concentrations of DMS (250 ppb) and isoprene (560~2248 ppb), both the model simulation and experimental data showed an increase in the yields of MSA and H2SO4 as the isoprene concentration increased.
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Tianyi Chen.
Publication Status: In Press
Funding: This work was supported by grants from the National Science Foundation (ATM-0852747) and the Alumni Scholarship from the University of Florida. Publication of this article was funded in part by the University of Florida Open-Access Publishing Fund.
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Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: All rights reserved by the submitter.
System ID: IR00001306:00001

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Atmos.Chem.Phys.,12,1 13 ,2012www.atmos-chem-phys.net/12/1/2012/doi:10.5194/acp-12-1-2012Authors2012.CCAttribution3.0License. Atmospheric Chemistry andPhysics ChambersimulationofphotooxidationofdimethylsuldeandisopreneinthepresenceofNOx T.ChenandM.JangDepartmentofEnvironmentalEngineeringSciences,P.O.Box116450,UniversityofFlorida,Gainesville,FL,32611,USACorrespondenceto:M.Jangmjang@u.eduReceived:17February2012PublishedinAtmos.Chem.Phys.Discuss.:8June2012Revised:19October2012Accepted:22October2012Published: Abstract.ToimprovethemodelpredictionfortheformationofH2SO4andmethanesulfonicacidMSA,aerosol-phasereactionsofgaseousdimethylsuldeDMSoxidationprod-ucts[e.g.,dimethylsulfoxideDMSO]inaerosolhavebeenincludedintheDMSkineticmodelwiththerecentlyreportedgas-phasereactionsandtheirrateconstants.Todeterminetherateconstantsofaerosol-phasereactionsofbothDMSOanditsmajorgaseousproducts[e.g.,dimethylsulfoneDMSO2andmethanesulnicacidMSIA],DMSOwasphotooxi-dizedinthepresenceofNOxusinga2m3Teonlmcham-ber.TherateconstantstestedintheDMSOkineticmech-anismswerethenincorporatedintotheDMSphotooxida-tionmechanism.Themodelsimulationusingthenewlycon-structedDMSoxidationmechanimswascomparedtocham-berdataobtainedfromthephototoxiationofDMSinthepresenceofNOx.Within120-minsimulation,thepredictedconcentrationsofMSAincreaseby200%andthoseofH2SO4,by50%duetoaerosol-phasechemistry.Thiswaswellsubstantiatedwithexperimentaldata.Tostudytheeffectofcoexistingvolatileorganiccompounds,thephotoox-idationofDMSinthepresenceofisopreneandNOxhasbeensimulatedusingthenewlyconstructedDMSkineticmodelintegratedwiththeMasterChemicalMechanismMCMforisopreneoxidation,andcomparedtochamberdata.WiththehighconcentrationsofDMSppbandisoprene2248ppb,boththemodelsimulationandexperimentaldatashowedanincreaseintheyieldsofMSAandH2SO4astheisopreneconcentrationincreased.1IntroductionDimethylsuldeDMSisamajorreducedsulfurcompoundofmarineorigin.ThemajoraerosolphaseproductsofDMSaremethanesulfonicacidMSAandsulfuricacidH2SO4 Bardoukietal. 2003 ; Baroneetal. 1995 ; Gastonetal. 2010 ; Lukacsetal. 2009 ,bothofwhicharepostulatedtohavesignicanteffectsontheearth'sradiationbudget Charlsonetal. 1987 .TheDMSphotooxidationmechanismisanimportantfactorforunderstandingtheroleDMSplaysintheearth'ssulfurcycleandclimatesystem,soithasbeenstudiedbymanyresearchers Yinetal. 1990a ; TurnipseedandRavishankara 1993 ; UrbanskiandWine 1999 ; Barnesetal. 2006 .Despitealltheeffortsexertedtounderstandingatmo-sphericDMSchemistry,alargediscrepancystillexistsbe-tweentheambientmeasurementsofDMSproductsandthesimulationresultsforcompoundssuchasDMSOdimethylsulfoxide Chenetal. 2000 ,H2SO4andMSA LucasandPrinn 2002 .ThepoorpredictivecapabilityofthekineticmodelfortheformationofDMSproductswascausedbyuncertaintiesintherateconstantsofDMSreactionsinthegasphase,thelackofaerosolphasereactionsoftheDMSproducts,andmissinginformationregardingtheimpactofvolatileorganiccompoundsVOContheDMSphotooxida-tionthroughboththegasandtheparticlephases.InthepresenceofUVlight,DMSoxidationisinitiatedbyOHradicalreactionsthroughboththehydrogenHab-stractionreactionandtheadditionreaction Atkinsonetal. 1989 .ItisknownthatDMSalsoreactswithO3P,NO3 Atkinsonetal. 1989 andNO2 BallaandHeicklen 1984 .TablesS1S3oftheSupplementsummarizethereactionmechanismsandtheirrateconstantsoftheDMSoxida-tionusedinthisstudy.TablesS1S3havebeenconstructedmainlybasedonthestudybyYinetal.a.Inthisstudy,someofreactionrateconstantshavebeenupdatedus-ingrecentlyreportedvaluesandnewreactionmechanisms PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion.

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2T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene e.g.,theDMSreactionwithDMSoriginradicalspecieshavealsobeenincludedinthisstudy.Forexample,therateconstants)]TJ/F63 7.572 Tf 5.906 0 Td[(1molecules)]TJ/F63 7.572 Tf 5.906 0 Td[(1cm3fortheOHradicalab-stractionreactionofDMSNo.59wassuggestedtobe1:1310)]TJ/F63 7.572 Tf 5.906 0 Td[(11exp.)]TJ/F63 9.963 Tf 7.771 0 Td[(254=T/by Atkinsonetal. 1997 ;therateconstantfortheOHradicaladditionreactiontoDMSONo.2wasupdatedto6:110)]TJ/F63 7.572 Tf 5.905 0 Td[(12exp.800=T/ Sanderetal. 2006 .TwootherinitialreactionsofDMSOoxidationNo.1and3werenewlyadded Sanderetal. 2006 .ThechangeofthereactionrateconstantsmayinuenceboththepredictionoftheDMSdecayanditsproductdistribution.AlthoughthepredictionofMSAandH2SO4isaffectedbydifferentgasmechanismsemployedinthemodel Karletal. 2007 ,thelargediscrepancyintheconcentrationsofMSAandH2SO4betweenobservationandmodelresultscannotbeexplainedsolelybytheuncertaintiesingasphasechemistry.Noexpressionofaerosol-phasereactionsintheDMSmech-anismisanotherreasonwhyMSAandH2SO4havebeenun-derpredictedusingtheexistinggasphasekineticmodel Yinetal. 1990a .Recenteldstudiesindicatethattheaerosol-phasereactionsofDMSproductssignicantlycontributetotheformationofMSAintheaerosol.Forexample,inaeldstudyintheequatorialPacic,Davisetal. 1999 indicatedthattheproductionofMSAthroughgastoparticlepartition-ingaccountforonly1%oftheobservedaerosolphaseMSA.Similarly,throughaneasternMediterraneancampaign,Mi-halopoulosetal. 2007 suggestedthatatleast80%oftheproductionofaerosolphaseMSAmaybeduetoaerosol-phasereactionsofDMSphotooxidationproductspossiblyDMSO.Campolongoetal. 1999 havefoundabettermatchbetweenthemeasuredMSAandthemodelpredictionwhentheaqueousphasereactionsoftheDMSoxidationproductswereconsidered.Bardoukietal. 2002 conrmedthattheliquidphasereactionsofDMSOandmethanesulnicacidMSIAwithOHradicalsproduceMSAwithhighyields.TobetterpredicttheatmosphericfateofDMS,thedevelopmentofanadvancedkineticmodelincorporatingaqueousphasechemistryisneeded.ThelackofconsiderationoftheimpactofVOContheDMSphotooxidationalsoaffectsthemodel'spredictiveabil-ityforDMSoxidationproductsinambientstudies.Inare-centindoorchamberstudy,ChenandJang 2012 discov-eredthattheMSAproductionfromDMSphotooxidationisaffectedbythepresenceofisoprene.However,nofurtherkineticstudiesoftheimpactofcoexistingVOCsonDMSchemistryhasbeenconducted.Inthisstudy,anewDMSkineticmodelwasdevelopedbyincludingnotonlythemostrecentlyreportedreactionsandtheirrateconstants Barnesetal. 2006 ; Sanderetal. 2006 ,butalsotheaerosol-phasereactionsofDMSgaseousproductsinaerosolphase.Todeterminetherateconstantsoftheaerosol-phasereactionsofbothDMSOanditsmajorgaseousproductsdimethylsulfoneDMSO2andmethane-sulnicacidMSIA,themodelwasrstsimulatedonthebasisoftheexperimentaldatafortheDMSOphotooxidationinthepresenceofNOxusinga2m3indoorchamber.TheresultingDMSOreactionswereincorporatedintothekineticmechanismsforsimulatingtheDMS.TostudytheinuenceofatmosphericVOCsonDMSoxi-dation,thenewDMSphotooxidationmechanismswaswerecoupledwiththeisoprenephotooxidationkineticmodelfromincludedintheMasterChemicalMechanismMCMv3.2 Jenkinetal. 1997 ; Saundersetal. 2003 ,whichisavail-able,viathewebsiteat: http://mcm.leeds.ac.uk/MCM/ .Theresultingmodelwasalsosimulatedforthechamberdata.Iso-prenehasbeenchosenasarepresentativeofthebiogenicVOCheremainlybecauseithasalargeemission660TgCyr)]TJ/F63 7.572 Tf 5.905 0 Td[(1 Guentheretal. 2006 anditisalsoknowntobeanimportantVOCfromtheocean Palmer 2005 .Inadditiontothehighuxofisoprene,thesecondaryor-ganicaerosolSOAyieldsfromisoprenearesensitivetotheaerosolacidityfromH2SO4 Czoschkeetal. 2003 ; Edneyetal. 2005 aswellasfromtheDMSphotooxidationprod-ucts ChenandJang 2012 .ItisthereforeinterestingtostudytheimpactofisopreneontheformationofDMSphotooxida-tionproducts.Fieldstudiesshowthatthemeanisopreneconcentrationintheremoteoceansandcoastalwatershedscanbeashighas300ppt,varyingwithtimeofday,seasonandlocation Shawetal. 2010 ,andthecoastalconcentrationofDMSisusually50ppt Ramanathanetal. 2001 .Inourstudythemix-ingratioofisoprenetoDMSwascontrolledbetween2and8tomimictheambientairincoastalwatersheds.TheNOxconcentrationweuseisintherangeof15ppb,repre-sentingareasofdifferentlevelsofanthropogenicairpollu-tion.AlthoughhalogencompoundsareknowntoreactfastwithDMS Barnesetal. 2006 ,inthecoastalareaswithhu-manactivities,OHradicalreactionswithDMSanditsprod-uctswillbedominant.Inthisstudy,wemainlyfocusontheOHradicalreactionwithDMS.2Experimentalsection2.1IndoorTeon-lmchamberexperimentsofphotooxidationofDMSOandDMS2.1.1ExperimentproceduresSincetheDMSOoxidationmechanismisanimportantsub-setofDMSoxidationmechanism,veDMSO/NOxexper-imentswereconductedtoevaluatetheDMSOsubmodel.Theexperimentswereconductedusinga2m3Teonin-doorchamberequippedwith16UVlampsSolarcSystemsInc.,FS40T12/UVBcoveringthewavelengthsbetween280and900nm.ThechamberwasushedusingairfromcleanairgeneratorsAadcoModel737,Rockville,MD;WhatmanModel75-52,Haverhill,MA.Priortoeachphotoirradiationexperiment,thechamberbackgroundairwasanalyzedtode-terminethecarryoverfromthepreviousexperimentse.g., Atmos.Chem.Phys.,12,1 13 ,2012www.atmos-chem-phys.net/12/1/2012/

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T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene3 Table1.ChamberexperimentsofthephotooxidationofDMSandDMSOinthepresenceofNOx. ExpTemp,CRH%aInitialsulfurconc.,ppbInitialNOconc.,ppbInitialNO2conc.,ppb DMSO-12224291.347.91.1DMSO-22226306.5199.10DMSO-3212399.132.01.0DMSO-42424170.079.75.3DMSO-5262775.732.01.0DMS-12428714.0102.71.0DMS-22628210.0116.83.1DMS-32528146.025.41.0DMS-42740134.021.50.5DMS-52560161.061.90 AccuracyofRH:2%;accuracyoftemperature:0.5C. Table2.ChamberexperimentalconditionsforisoprenephotooxidationwithandwithoutDMS. ExpTemp,CaRH%aInitialDMSconc.,ppbInitialisopreneconc.,ppbInitialNOconc.,ppbInitialNO2conc.,ppb iso-124.530064466.710.2iso-225.032060020.06.7iso-DMS-123.52824356077.37.5iso-DMS-223.230265136079.94.6iso-DMS-323.030276224862.03.9iso-DMS-422.0103121039.01.3iso-DMS-523.13020b40b15.60 aAccuracyofRH:%;accuracyoftemperature:.5C.bInitialDMSandisopreneconcentrationsiniso-DMS-5wereestimatedbasedontheamountofinjectedchemicalsduetotheinstrumentaldetectionlimit. DMSOandDMSO2.ThechamberhumiditywascontrolledbyintroducinghumidiedairstreamsintothechamberuntiltherelativehumidityRHinthechamberreachedthede-siredvalue.TheRHwasmeasuredatthebeginningofexper-imentandcorrectedfortemperaturechangeupto5Koverthecourseoftheexperiment.Afterushingthechamberwiththecleanair,thebackgroundaerosolconcentrationwasbe-low0.20gm)]TJ/F63 7.572 Tf 5.906 0 Td[(3andtheconcentrationsoftheDMSOandDMSO2werebelow2%oftheinitialsulfurconcentrationsTables1,2and3ofeachchamberexperiment.DMSOwasaddedtothechamberbypassingcleanairthroughaTunionwhereDMSO.6%,Sigma-Aldrichwasinjectedusingasyringeandgentlyheatedusingaheatgun.CCl4wasinjectedforchamberdilution.NOx.5%nitricoxide,Airgaswasinjectedintothechamberbyinsertingasyringethroughtheinjectionports.WhentheinitialconcentrationofNOxwasstable,UVlampswereturnedon.TheproceduresoftheDMS/NOxexperimentsweresameasthoseoftheDMSO/NOxexperimentsexceptthatDMS.7%,Aldrichwasinjectedintothechamberusingasy-ringewithoutheating.ThedetailedexperimentalconditionsforDMSOandDMSphotooxidationreactionsaresumma-rizedinTable1.2.1.2InstrumentationandsampleanalysisTheconcentrationsofDMS,SO2,NOxandO3inthecham-berweremeasuredusinganHP5890gaschromatography-ameionizationdetectorGC-FID,auorescenceTRSanalyzerTeledyneModel102E,achemiluminescenceNO/NOxanalyzerTeledyneModel200EandaphotometricozoneanalyzerTeledynemodel400E.Particleconcentra-tionsweremeasuredusingascanningmobilityparticlesizerSMPS,TSI,Model3080,MNcombinedwithacondensa-tionnucleicounterCNC,TSI,Model3025A.Aparticle-into-liquidsamplerApplikon,ADI2081coupledwithanionchromatographyMetrohm,761CompactICPILS-ICwasusedtomeasurethemajoraerosolproductse.g.,MSAandH2SO4producedfromDMSphotooxidation.Thedetec-tionlimitofPILS-ICis0.1gm)]TJ/F63 7.572 Tf 5.906 0 Td[(3andtheassociatederroris10%.DMSOandDMSO2werecollectedusingaliquidN2)]TJ/F63 9.963 Tf 17.756 0 Td[(195Ctrapfor8minataowrateof3Lmin)]TJ/F63 7.572 Tf 5.906 0 Td[(1.3mlofacetonitrileoptimagradewithdeuteratedDMSOd6-DMSO,usedasaninternalstandardwerethenaddedtothetrap,whichwassubsequentlycappedandimmersedintohotwater60Cfor10min.TheliquidinthetrapwasthentransferredtoasmallvialforchromatographyiontrapmassspectrometerGC-ITMS,VarianmodelCP-3800GC,Saturnmodel2200MSanalysis.TheanalysisofDMSOand www.atmos-chem-phys.net/12/1/2012/Atmos.Chem.Phys.,12,1 13 ,2012

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4T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene Table3.ModelsimulationoftheyieldsofMSAandH2SO4andtheintegratingreactionratesIRRoftheformationofMSAandH2SO4inthepresenceofdifferentamountofisoprenea. IRRnormalizedby1DMSb ExpIsopreneSim.timec,1DMS,MolaryielddMSAH2SO4 ppbminppbMSAH2SO4gaspathwayeaerosolpathwayfgaspathwayeaerosolpathwayf iso-DMS-1560446.410.3%.3%1.0%.7%0.09700.0090iso-DMS-21360505.912.2%.7%1.2%.8%0.1050.0020.0120iso-DMS-322481636.013.1%.1%2.0%.3%0.1150.0050.0220 aAllthereportedresultsexceptthoseinbracketsinthistablewerebasedonthemodelsimulation.Theexperimentalyielddataareinthebrackets.TheMSAyieldsinthistablewerecalculatedusingthedatafromFig.4withcorrectionsforDMSwalllossandchamberdilution.NotethattheDMSdecayinFig.4containsthedecayduetophotooxidation,walllossandchamberdilution.bReferto3.3.1forthedescriptionofIRR.cThesimulationtimewassetsothattheconsumedDMSwasxedataround6ppbforfaircomparisonamongdifferentsystems.dMolaryieldisdenedastheamountofMSAorH2SO4formeddividedbytheamountaround6ppbofDMSconsumed.eTheIRRforReactionR48andR54inTableS1andReactionR132inTableS2wereaddedupforMSAformationwhiletheIRRforReactionR170andR171inTableS3wereaddedupforH2SO4formation.fTheIRRforMSAformationwasbasedonReactionR8inSect.3.1.2andthatforH2SO4formationwasfromReactionR9inthesamesection. DMSO2insolutionusingGC-ITMShasbeenpresentedbyTakeuchietal. 2010 .TheGCtemperatureproleinourstudyis70Cfor1min;rampto90Cat5Cmin)]TJ/F63 7.572 Tf 5.906 0 Td[(1;rampto280Cat20Cmin)]TJ/F63 7.572 Tf 5.906 0 Td[(1andholdfor8min.FigureS1intheSupplementsummarizestheretentiontimeandmassspectraofDMSO,DMSO2andd6-DMSOfortheGC/MSanalysis.TheconcentrationsofDMSOandDMSO2weredeterminedbythecalibrationcurveproducedusingauthenticstandardswithaninternalstandardd6-DMSO.TheassociatederrorwiththemeasuredconcentrationsofDMSOandDMSO2is%.2.2IndoorTeon-lmchamberexperimentsofDMSphotooxidationinthepresenceofisopreneInadditiontothemonitoringofozone,NOx,andDMS,majorisoprenephotooxidationproducts[methacroleinP1,methylvinylketoneP2,glyoxalP3,andmethylglyoxalP4]weresampledevery30minminsamplingfor2.5hsamplesintotalwithaowrateof1.0Lmin)]TJ/F63 7.572 Tf 5.906 0 Td[(1usinganimpingerthatcontained12mLofacetonitrilewithbornylacetateinternalstandard.Furtherdescrip-tionsofderivatizationmethodsforcarbonylsO-,3,4,5,6-Pentauorobenzyl-hydroxylaminehydrochloride,PFBHAcanbefoundelsewhere Imetal. 2011 .AlltheimpingersampleswereanalyzedbytheGC-ITMSwiththetemperatureprogramasfollows:80Cfor1min;rampto100at5Cmin)]TJ/F63 7.572 Tf 5.906 0 Td[(1;holdfor3min;rampto280Cat10Cmin)]TJ/F63 7.572 Tf 5.906 0 Td[(1andholdfor8min.Thedescriptionofdetailedanalyticalproceduresforthequanticationofproductscanbefoundinthepreviousstudy Imetal. 2011 .TheerrorsassociatedwiththeGC/MSanalysesforisopreneproductsare%.3Resultsanddiscussion3.1Kineticmodel3.1.1ReactionmechanismsofDMSDMSphotooxidationinthepresenceofNOxintheindoorchamberwassimulatedusingexplicitkineticmechanismsin-tegratedwiththeMorphokineticsolverJeffries,1998.Ta-blesS1intheSupplementsummarizethekineticmecha-nismsrelatedtoDMSoxidationalongwiththeirreactionrateconstants,whichwerecollectedfromtherecentliterature.Thereactionrateconstantsoftheoxidationforthenon-sulfurcompoundse.g.,formaldehyde,methanol,andmethane,etcareobtainedfromtheMCMmechanisms Jenkinetal. 1997 ; Saundersetal. 2003 .3.1.2FormationofMSAandH2SO4throughaerosol-phasereactionsofgaseousDMSoxidationproductsForthepredictionofDMSoxidationproductsinaerosol,mostexplicitmodelsexpressingDMSphotooxidatione.g.,Yinetal., 1990a inthegasphaselackthedescriptionofaerosol-phasechemistryofDMSoxidationproducts.Inthemodelofthisstudy,weassumedthatDMSOpro-ducesMSIA,whichconsequentlyformsMSAintheaerosolphase Bardoukietal. 2002 ,andDMSO2producesH2SO4throughaerosol-phasereactions KogaandTanaka 1993 .Theaerosol-phasereactionofSO2inH2SO4aerosolhasbeenfoundinsignicant Rattiganetal. 2000 ,soitisnotincludedinthemodel.ThenucleationofgaseousMSAandH2SO4originatingfromDMSphotooxidationproducesanaerosolmasssuitableforpartitioningoforganiccompounds.Inourmodel,bothMSAandH2SO4arepredominantlypresentintheaerosol Atmos.Chem.Phys.,12,1 13 ,2012www.atmos-chem-phys.net/12/1/2012/

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T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene5 phaseandtheirtotalmassisexpressedasAerosolinthismechanism.TAerosolUDTH2SO4UCTMSAUwheresquaredbracketsdenoteconcentration.TheDMSOpresentinthegasphaseisdenotedasCH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/CH3g.Inthesameway,thegasphaseMSIAisdenotedasCH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/OHgandthegasphaseDMSO2isde-notedasCH3.O/S.O/CH3g.Theparticlephase,DMSO,MSIA,andDMSO2aredescribedasCH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/CH3p,CH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/OHpandCH3.O/S.O/CH3p,respectively.Inordertoincludeaerosol-phasereactionsofgaseousDMSoxidationproducts,theratesofabsorptionikabs,cm3molecules)]TJ/F63 7.572 Tf 5.906 0 Td[(1s)]TJ/F63 7.572 Tf 5.906 0 Td[(1anddesorptionikdes,s)]TJ/F63 7.572 Tf 5.906 0 Td[(1ofthegaseousorganiccompounds Kamensetal. 1999 ,havebeenaddedtothenewmodel.Theikabs/ikdesvalueisequaltotheequilibriumconstant,iKp,forthegas-particleequilibriumofagivenpartitioningcompound.iKpDikabs=ikdesiKpisestimatedusingthefollowingequation Pankow 1994 ,iKpD7:501RT=.109MWiipL/whereMWistheaveragemolecularweightoftheaerosolmediume.g.,45gmol)]TJ/F63 7.572 Tf 5.906 0 Td[(1atrelativehumidity=30%,ipListhevaporpressureofcompoundi,andiistheactivitycoefcientofcompoundiatagivenmedium.TheivaluesforthecompoundsDMSO,DMSO2andMSIAofinterestinthisstudyareunknown.ForDMSO,theivalueisesti-matedfromtherelationshipbetweeniKpandHenry'slawconstantH.iKp HD7:501RTV 109MWwhereVismolarvolumeofthemedium.ThecalculatediKpvalueofDMSOis1.310)]TJ/F63 9.963 Tf 6.404 -3.617 Td[(5gm)]TJ/F63 9.963 Tf 6.404 -3.617 Td[(3andtheestimatediis0.023atTD298K.ThentheiforDMSOwasappliedtotheestimationofiKpvaluesofDMSO2andMSIAusingEq.3althoughtheivalueofDMSOmightbedifferentfromthoseofDMSO2andMSIA.ThedetaileddescriptionofthedeterminationofikabsandikdesisshownintheSupplement.Inbrief,basedontheanal-ysisofthecharacterizationtimes,theequilibriumpro-cesseq=101sgovernedbytheabsorptionandthedes-orptionprocessesofthecompoundbetweenthegasandtheparticleismuchfasterthanthereactioninthegasphasegas=105s.Hence,thedeterminationoftheabsoluteval-uesofikabsandikdesbecomeslessimportantaslongasthevaluesofbothabsorptionanddesorptionaremuchshorterwithincomputerprocesstimethanthatofgas-phasereac-tion.Inthisstudy,thevalueoftheabsorptionprocessissetto10)]TJ/F63 7.572 Tf 5.906 0 Td[(4sandisappliedtotheestimationofbothikabsandikdes.Theofthedesorptionprocessofallthreecompoundsareintheorderof10)]TJ/F63 7.572 Tf 5.906 0 Td[(8s.ThepartitioningprocessesofDMSO,MSIAandDMSO2aredescribedasfollows. CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/CH3.g/CAerosol!CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/CH3.p/CAerosol R1 ikabsD1:410)]TJ/F63 7.572 Tf 5.906 0 Td[(6 CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/CH3.p/!CH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/CH3.g/ R2 ikdesD3:8108 CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/OH.g/CAerosol!CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/OH.p/CAerosol R3 ikabsD1:410)]TJ/F63 7.572 Tf 5.906 0 Td[(6 CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/OH.p/!CH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/OH.g/ R4 ikdesD2:4107 CH3.O/S.O/CH3.g/CAerosol!CH3.O/S.O/CH3.p/CAerosol R5 ikabsD1:410)]TJ/F63 7.572 Tf 5.906 0 Td[(6 CH3.O/S.O/CH3.p/!CH3.O/S.O/CH3.g/ R6 ikdesD3:0107Thereactionsofaerosol-phaseoxidationofDMSO,MSIAandDMSO2inaerosolbulkphasearedescribedasfollows.CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/CH3.p/h)460(!CH3)]TJ/F63 9.963 Tf 7.771 0 Td[(S.O/OH.p/ikr=4:8 R7 CH3)]TJ/F63 9.963 Tf 7.77 0 Td[(S.O/OH.p/h)460(!CH3)]TJ/F63 9.963 Tf 7.771 0 Td[(SO3Hikr=5:6 R8 CH3.O/S.O/CH3.p/h)460(!CH3)]TJ/F63 9.963 Tf 7.771 0 Td[(SO3Hikr=2:410)]TJ/F63 7.572 Tf 5.906 0 Td[(3 R9 whereikrs)]TJ/F63 7.572 Tf 5.906 0 Td[(1istherateconstantfortheaerosol-phasereactionofcompoundi.ikrvaluesinReactionsR7R9wereempiricallydeterminedbyttingthepredictedconcen-trationsofMSAandH2SO4totheexperimentallyobservedconcentrations.Themajoroxidantsintheaerosolphasere-actionofDMSO,DMSO2andMSIAareOHradicals Bar-doukietal. 2002 .TheproductionofOHradicalsinthepar-ticlephaseiscomplexduetothephotolysisofvariousOHradicalprecursorsROOH,H2O2,andHONOandthepar-titioningofgasphaseOHradicalstotheparticle.HencetheproductionofOHradicalsintheaerosoldependsonlightintensity.Inthisstudy,weassumethattheconcentrationoftheparticlephaseOHradicalisproportionaltolightinten-sity.Theaerosol-phasechemistryiscontrolledbyasingleikrvalueforeachaerosolphasereactioninReactionsR7R9sinceapparentreactionrateconstantsformultiphasereac-tionsareobtainedbyttingtotheexperimentaldata.Basedontheanalysisofthechemicaluxusingtheintegratedre-actionratesinthemodel,theconsumptionofOHradicalsthroughmechanismsReactionsR7R9arelessthan3%ofthetotalOHradicalsinthesystemsuggestingthatcon-sumptionofOHradicalsthroughaerosol-phasereactionsisinsignicant. www.atmos-chem-phys.net/12/1/2012/Atmos.Chem.Phys.,12,1 13 ,2012

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6T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene Fig.1.TimeprolesofDMSO,DMSO2,SO2,NOxandO3forthephotooxidationofDMSOinthepresenceofNOxExpDMSO-1andDMSO-2inTable1.EdenotestheexperimentallyobservedconcentrationsofchemicalspeciesandSforthosesimulatedusingthekineticmodel.ThedecayofDMSOwasnotcorrectedforthewalllossandchamberdilution. 3.1.3IsopreneoxidationmechanismThekineticmechanismsofisopreneoxidationhavebeende-scribedusingtheMCMv3.2Jenkinetal.,1997;Saundersetal.,2003andcomparedtothedatafromtwoexperimentsExpiso-1andExpiso-2inTable2withdifferentNOxconcentrations.Welzetal. 2012 haverecentlymeasuredtheupperlimitoftherateconstantsforthereactionofthestabilizedCriegeeradicalCH2OOwithanumberofim-portantatmosphericspecies,concludingthatthereactionsofCH2OOwithNO2.010)]TJ/F63 7.572 Tf 5.906 0 Td[(12cm3molecules)]TJ/F63 7.572 Tf 5.906 0 Td[(1s)]TJ/F63 7.572 Tf 5.906 0 Td[(1andwithSO2.910)]TJ/F63 7.572 Tf 5.906 0 Td[(11cm3molecules)]TJ/F63 7.572 Tf 5.906 0 Td[(1s)]TJ/F63 7.572 Tf 5.906 0 Td[(1aremuchfasterthanthepreviousestimation.Thesenewreactionratecon-stantswereusedtoupdatetheoriginalconstantsintheMCMv3.2.3.2DMSmodelsimulation3.2.1ChambercharacterizationThephotolysisratesofinorganicspeciesandorganiccom-poundswerecalculatedusingthechemicalsolverintegratedwiththewavelength-dependentabsorptioncross-sectionalareas,quantumyields,andthechamberlightintensity.ThelightspectruminsidethechamberwasmeasuredusingaspectroradiometerPS-300,Apogee.Forthecalibrationofthelightintensityinsidethechamber,anNO2photolysisex-perimentwasseparatelyconductedunderthenitrogengas.95%environment.Thedetaileddescriptionofthelightcharacterizationprocedurecanbefoundinthepreviousstudy Cao 2008 .ThechamberwalllossofoxidantgasessuchasO3andH2O2weredeterminedthroughseveraldarkchamberexper-iments.Theirwalllossratesareestimatedusingarstor-derrateconstants)]TJ/F63 7.572 Tf 5.906 0 Td[(1:2:510)]TJ/F63 7.572 Tf 5.906 0 Td[(5forO3and6:710)]TJ/F63 7.572 Tf 5.906 0 Td[(4forH2O2.ThewalllossrateconstantsofDMS10)]TJ/F63 7.572 Tf 5.905 0 Td[(6s)]TJ/F63 7.572 Tf 5.905 0 Td[(1,SO210)]TJ/F63 7.572 Tf 5.906 0 Td[(5s)]TJ/F63 7.572 Tf 5.905 0 Td[(1,DMSO10)]TJ/F63 7.572 Tf 5.906 0 Td[(5s)]TJ/F63 7.572 Tf 5.906 0 Td[(1andDMSO210)]TJ/F63 7.572 Tf 5.906 0 Td[(5s)]TJ/F63 7.572 Tf 5.906 0 Td[(1werealsoexperimentallydeterminedassumingtherstorderrateandappliedtothereactionmechanismsTa-bleS1tocomparethesimulatedresultstotheexperimen-taldata.TableS4summarizesthewalllossrateconstantsofthecompoundsofthisstudyandthosefoundinliterature Qietal. 2007 ; Ballesterosetal. 2002 ; Yinetal. 1990a .ForMSAandH2SO4,predominantlypresentinaerosol,theirwalllosswascalculatedusingtheaerosoldataassumingtherstorderdecayasafunctionoftheaerosolsize McMurryandGrosjean 1985 .DetailsoftheauxiliarymechanismthatincludesthewallchemistryofNOyspeciesweredescribedbyJeffriesetal. 2000 .Thebackgroundgasesinthechamber,suchasmethane.8ppm,formaldehydeppbandacetaldehydeppb,wereincludedinthemodelsimulation.Methaneisubiq-uitouswithaconstantconcentration.Theconcentrationsofformaldehydeandacetaldehydeinthechamberwere Atmos.Chem.Phys.,12,1 13 ,2012www.atmos-chem-phys.net/12/1/2012/

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T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene7 Fig.2.ModelsimulationofMSAandH2SO4forthephotooxida-tionofDMSOinthepresenceofNOxExpDMSO-1andDMSO-2inTable1withSHandwithoutSNincludingaerosol-phasere-actions.TheexperimentallyobservedconcentrationsEofMSAandH2SO4areshownascomparison.TheproductionofMSAandH2SO4wascorrectedforwallloss. determinedusingGC-ITMSintegratedwithPFBHAderiva-tization.3.2.2DMSOphotooxidationSincetheDMSOphotooxidationmechanismisanimportantpartofDMSphotooxidationmechanism,beforetheevalu-ationoftheDMSphotooxidationmodel,theDMSOsub-modelwasevaluated.FiveDMSOphotooxidationexperi-mentsExpDMSO-1,ExpDMSO-2,ExpDMSO-3,ExpDMSO-4andExpDMSO-5inTable1wereconductedtoconrmtheDMSOsubmodel.ThemodelsimulationofDMSOdecay,theprolesofDMSO2,SO2,NOxandO3agreedwithobservationsExpDMSO-1andExpDMSO-2inFig.1.Withoutincludingtheaerosol-phasereactionsEq.R1R9,MSAconcentrationsaresignicantlyunder-estimated.Asanexample,thesimulationsversusobserva-tionExpDMSO-1andExpDMSO-2beforeandafterin-cludingtheaerosol-phasereactionsareshowninFig.2.Fig-uresS2andS3summarizethecorrespondinginformationforExpDMSO-3,ExpDMSO-4andExpDMSO-5inTable1.TheprolesofNOx,O3andSO2werenotinuencedbytheaerosol-phasereactions.3.2.3DMSphotooxidationTheDMSOsubmodelthatcontainsaerosol-phasereactionsofDMSproductsisincludedintheDMSoxidationmech-anism.ThenewDMSchemistryschemewassimulatedagainstveDMSphotooxidationexperiments.Inthemodelofthisstudy,thereactionofDMSwiththeCH3Sradical,thedecompositionoftheCH3-SO3radicalandthereactionoftheCH3OSOradicalwithNO2werealsoincluded.Thesereactionshavebeeneithermissedorassignedwithimproperestimatesofreactionrateconstantsintheexistingmodels Yinetal. 1990a .ThepredictionofDMSdecayandDMSproductformationareimprovedaftermodicationofthereactions.Barnesetal. 1988 proposedtheDMS+CH3SreactioninordertoexplainthefastdecayofDMSinthepresenceofNOx.Itwasfoundthat,withoutthisreaction,themodelsimulationofDMSdecayissystematicallyslowerthanob-servation.TheDMS+CH3SreactionReactionNo.103inTableS2wasthusaddedtothemodelwithanestimatedrateconstantsothatthedecayofDMSandtheprolesofNOxandO3ofthesimulationresultcouldbebestttedtothatofobservationinourstudy.ThereportedreactionrateconstantofthedecompositionoftheCH3-SO3radicalreactionNo.46inTableS1spansbetween0.004and51s)]TJ/F63 7.572 Tf 5.906 0 Td[(1 Campolongoetal. 1999 .Itwaspreviouslyestimatedtobe0.16s)]TJ/F63 7.572 Tf 5.905 0 Td[(1withoutexperimentalconrmation Yinetal. 1990a .Inthisstudy,itwasfoundthatthechangeofthisrateconstantdoesnotsignicantlyin-uencetheDMSdecayortheNOxprole;rather,itimpactsthedistributionofH2SO4andMSA.Avalueof0.04s)]TJ/F63 7.572 Tf 5.906 0 Td[(1wasfoundtobesttthemeasuredconcentrationsofaerosol-phaseH2SO4andMSA.TherateconstantofthereactionbetweentheCH3OSOradicalandNO2reactionNo.24inTableS1wasreportedtobe.21.110)]TJ/F63 7.572 Tf 5.905 0 Td[(12cm3molecule)]TJ/F63 7.572 Tf 5.906 0 Td[(1s)]TJ/F63 7.572 Tf 5.906 0 Td[(1 Rayetal. 2010 withonestandarddeviationoferror.Inthisstudy,avalueof510)]TJ/F63 7.572 Tf 5.906 0 Td[(13withintwostandarddeviationoferrorofRay'sdatawasfoundtobestttheSO2andacidformationprole.ThemajorgaseousproductsofDMSoxidationweresim-ulatedandareshowninFig.3aforExpDMS-3,ExpDMS-4andExpDMS-5andFig.S4forExpDMS-1andExpDMS-2.Ingeneral,SO2andDMSO2werereasonablypre-dicted.ThemeasuredDMSOconcentrationsintheexperi-mentscontainingDMSwerenotreportedinthisstudyseeArtifactsofDMSOmeasurementinthepresenceofDMSsectionintheSupplement.Foraerosol-phaseproducts,themodelunderestimatedtheconcentrationsofMSAandH2SO4byuptoafactorofthreeduringtherst60minofchamberexperiments,butfollowedthemeasurementsmorecloselyduringtherestoftheexperimentsFigs.3candS4c.Inthemodel,aerosol-phasereactionsassociatedwithDMSO,MSIA,andDMSO2arecontrolledbypartitioningprocessesthataregovernedmainlybytheaerosolmass.However,intheearlystageof www.atmos-chem-phys.net/12/1/2012/Atmos.Chem.Phys.,12,1 13 ,2012

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8T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene Fig.3.TimeprolesofDMS,DMSO2,SO2,MSA,H2SO4,NOxandO3forthephotooxidationofDMSOinthepresenceofNOxExpDMS-3,ExpDMS-4andExpDMS-5inTable1.EdenotestheexperimentallyobservedconcentrationsofchemicalspeciesandSforthosesimulatedusingthekineticmodel. theexperiment,aerosolsaresmallbecausetheyareformedvianucleation,sotheirsurfaceareawouldbemuchmoreimportantthantheirmassinthepartitioningprocesses.Themodel'spredictionslimittheaccommodationofDMSO,MSIA,andDMSO2duetothemass-basedpartitioningpro-cessesinthemodel.Consequently,theproductionofMSAandH2SO4intheearlystageofthechamberexperimentswasunderpredictedinthemodelofthisstudy.3.3ImpactofthecoexistingisopreneonDMSphotooxidation3.3.1IsoprenephotooxidationTheMCMv3.2includescomprehensiveisoprenephotoox-idationmechanismsincludingsomeveryrecentlyproposedmechanismssuchasepoxideformation Paulotetal. 2009 .TheisoprenemodelwassimulatedagainstExpiso-1andExpiso-2.ThemajorproductsP1P4originatingfromisoprenewerealsosimulatedandcomparedtoexperimentallymea-suredconcentrations.Themassspectradataforisoprene'smajorgaseousproductsaresummarizedinFig.S6andthesimulationresultsareplottedagainstobservationinFig.S6.Overall,theMCMmechanismpredictstheisoprenedecay,theformationofseveralisopreneproductsandtheprolesofNOxandO3well.3.3.2DMSphotooxidationinthepresenceofisopreneExperimentsiso-DMS-1,iso-DMS-2andiso-DMS-3werecarriedoutundersimilarinitialconcentrationsofDMSandNOx.ThesimulationprolesofDMS,isoprene,MSAandH2SO4areshowninFig.4incomparisonwiththemeasure-ments.TheconcentrationsofNOx,O3andthegasphaseproductsP1P4originatingfromisopreneoxidationarewellpredictedusingthekineticmodelFig.S7.TounderstandtheimpactofisopreneontheproductionofMSAandH2SO4,molaryieldsdenedastheamountofaproducedproductdividedbytheamountoftheconsumedDMSofMSAandH2SO4werecomparedbetweenexperi-mentswithdifferentinitialisopreneconcentrationswithsim-ilaramountsofDMSconsumption.TheyieldsofMSAandH2SO4inTable3werefoundtoincreaseastheinitialiso-preneincreasesforboththemodelsimulationandexperi-mentaldataaftercorrectionforwalllossandchamberdilu-tion.TounderstandtheimpactofisopreneonyieldsofMSAandH2SO4,thecontributionofgas-phasereactionsandaerosol-phasechemistryofDMSphotooxidationtothefor-mationofMSAandH2SO4wereanalyzedusingtheinte-gratedreactionrateIRRasshowninTable3.Theintegratedreactionrate,expressedasanaccumulateduxofchemicalformationorconsumptionatagivenreactionandanini-tialconcentration,isestimatedusingtheMorphochemical Atmos.Chem.Phys.,12,1 13 ,2012www.atmos-chem-phys.net/12/1/2012/

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T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene9 Fig.4.Timeprolesofisoprene,DMS,MSAandH2SO4forthephotooxidationofDMSandNOxinthepresenceof560ppbExpiso-DMS-1,1360ppbExpiso-DMS-2,and2248ppbExpiso-DMS-3ofisoprene.EdenotestheexperimentallyobservedconcentrationsofchemicalspeciesandSforthosesimulatedusingthekineticmodel.ThedecayofDMSandisoprenewasnotcorrectedforthewalllossandchamberdilutionwhiletheproductionofMSAandH2SO4wascorrectedforwallloss. solver.Overall,theIRRvaluesoftheformationofbothMSAandH2SO4increasewiththeincreasinginitialisoprenecon-centration.TheIRRanalysissuggeststhathigherinitialisoprenecon-centrationsenhancetheformationofSO2,consequentlyin-creasingtheproductionofH2SO4.TheIRRTableS5ofDMSwithO3Pwasfoundtobethemajorvariantamongtheexperimentswithdifferentlevelsofisopreneconcentra-tion.ThecoexistingisopreneefcientlyincreasesNOxcy-clesduringDMSphotooxidationandalsoincreasesthereac-tionofDMSwithO3PReactionNo.61inTableS2,pro-ducingaCH3-SOradicalwithaunityyield.TheresultingCH3-SOisefcientlyoxidizedintoaCH3OSOradicalthatisknowntobeacriticalintermediatefortheformationofSO2andMSA Yinetal. 1990a .TheeffectofisopreneonMSAproductioniscomplicatedbecauseisopreneinuencesbothgas-phasereactionsandaerosol-phasereactions.SimilarlytoH2SO4,MSAforma-tioninthegasphaseisincreasedwithhigherisoprenecon-centrationsduetothehigherproductionoftheCH3OSOradical.MSAandH2SO4producedthroughthegasphasemechanismsprovideadditionalaerosolmassandconse-quentlyincreasetheMSAformationintheaerosolphasethroughtheaerosol-phasereactionsofDMSoxidationprod-ucts.AlthoughthenewlybuiltDMSkineticmodelofthisstudysuccessfullypredictsthetrendTable3intheyieldsofMSAandH2SO4underdifferentinitialisopreneconcentrations,themodel'spredictionssomewhatdeviatefromexperimen-taldatawhentheisopreneconcentrationishigh.Similarly,forExpiso-DMS-1,Expiso-DMS-2andExpiso-DMS-3inFig.4,themodelunderpredictsMSAconcentrations.Thegapbetweenmeasurementandpredictionincreasesastheinitialisopreneconcentrationincreases.ItisexpectedthatthesecondaryorganicaerosolSOAformedfromisoprenephotooxidationwouldinuencetheformationofMSA,pos-siblybecausetheSOAmightincreasethesolubilityofDMSproductssuchasDMSO.Theaerosol-phasechemistryonisopreneSOAisnotincludedinthisstudyandthismaypos-siblyleadtothedeviationofthemodel'spredictionsfromexperimentaldata. www.atmos-chem-phys.net/12/1/2012/Atmos.Chem.Phys.,12,1 13 ,2012

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10T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene Fig.5.TimeprolesofExpiso-DMS-4isoprene,DMS,NOxandO3fromthephotooxidationof31ppbofDMSand40ppbofNOxinthepresenceof210ppbofisopreneandtimeprolesforExpiso-DMS-5NOx,O3,MSAandH2SO4from20ppbofDMSand15ppbofNOxinthepresenceof40ppbofisoprene.EdenotestheexperimentallyobservedconcentrationsofchemicalspeciesandSforthosesimulatedusingthekineticmodel.ThedecayofDMSandisoprenewasnotcorrectedforthewalllossandchamberdilutionwhiletheproductionofMSAandH2SO4wascorrectedforwallloss. 3.4PotentialapplicationofthekineticmodelinambientsimulationToevaluatethemodel'sperformanceforlowerconcen-trationsofisopreneandDMS,Expiso-DMS-4isoprene:210ppb,DMS:31ppbandExpiso-DMS-5isoprene:40ppb,DMS:20ppbwereconducted.ThesimulationagreeswellwithmeasurementsFig.5forbothgas-phaseandaerosol-phaseproducts.Duetothedetectionlimitsofinstruments,chamberexperimentsrelevanttoambientcon-centrationsofisopreneandDMScannotbeconductedinthisstudybutsimulatedusingthekineticmodel.ThesimulationofthephotooxidationoflowerconcentrationsofisopreneandDMSisbenecialtoevaluatetheeffectofbothNOxandisopreneontheyieldsofMSAandH2SO4andtoun-derstandtheroleoftheaerosol-phasereactionsofDMSox-idationproductsinthepredictionoftheproductionofMSAandH2SO4.FigureS8showsthathigherNOxconcentrationincreasestheyieldsofbothMSAandH2SO4for0.5ppbofinitialDMS,whichhasbeendiscussedbyYinetal. 1990b .An-otherconclusionfromFigureS8isthatinthelowconcen-trationexperiment,theyieldofH2SO4ishigherthanthatofMSA.ThisisbecausethedecompositionofCH3-SO3re-actionNo.46thatproducesSO3becomessignicantcom-paredwithitsreactionwithotheroxidantsthatproducesMSA.FigureS9illustratestheimpactoftheisopreneconcen-trationontheyieldsofMSAandH2SO4inthepresenceof0.5ppbofinitialDMS.Intheearlystage,isoprenehasasim-ilarimpactontheyieldsofMSAandH2SO4asobservedinhighconcentrationexperiments.Asreactionsprogress,theyieldsofMSAandH2SO4tendtodecreasewiththeincreaseofinitialisopreneconcentration.BecauseisoprenecompeteswithitsoxidationproductsforatmosphericoxidantssuchasOHandNO3radicals,thereactionsofCH3OSOwithatmsoperhicoxidantsbecomelessimportantandthedecom-positionofCH3OSOreactionNo.27toSO2ismoreimportant.SO2yieldhasbeenconrmedthroughthemodelsimulationshowingsignicantincreaseswithincreasingiso-preneconcentrations.SincethereactionsofCH3OSOwithatmosphericoxidantsarethemainsourcesofMSAandH2SO4,theyieldsofbothMSAandH2SO4decreasesinthelaterstageofexperimentswiththehighconcentrationofiso-prene.Themodelsimulationalsoshowsthattheinclusionofaerosol-phasereactionsinthemodeldoesnotchangethepre-dictionofMSAandH2SO4forthelowconcentrationexper-iments.Apossiblereasonisthattheaerosol-phasereactionsrequireaerosolmass,butinthesimulationtheinitialaerosolmassiszerowhichmakestheaerosol-phasereactionsveryslow.Intheambientaerosol,thereispreexistingaerosolsthatcanfacilitatetheaerosol-phasereactionsofthesemivolatileproductsfromDMSphotooxidation.Inordertotesttheim-portanceoftheaerosol-phasereactionsinthepredictionof Atmos.Chem.Phys.,12,1 13 ,2012www.atmos-chem-phys.net/12/1/2012/

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T.ChenandM.Jang:SimulationofDMSphotooxidationwithisoprene11 acidformation,a4gm)]TJ/F63 7.572 Tf 5.906 0 Td[(3ofinitialseedwasincludedinthemodel.Thesimulationwithandwithoutthepresenceofini-tialseedsisshowninFig.S10.TheMSAconcentrationinthepresenceofinitialseedsincreasesby20%%com-paredtothatwithoutinitialseedwithin4-hoursimulation.WeconcludethatthenewlyconstructedDMSkineticmodelcanimprovethepredictionofMSAintheambientair.4ConclusionandatmosphericimplicationInthisstudy,themodelingofDMSoxidationmechanismshasbeenadvancedbyincludingboththemostrecentreactionrateconstantsandaerosol-phasereactionsofgas-phaseDMSoxidationproductsintheaerosol.Thenewlyconstructedki-neticmodelcloselymatchestheexperimentaldatafortheDMSdecayandtimeprolesofNOx,O3,SO2andDMSO2.ThepredictionofH2SO4andMSAconcentrationshasbeensignicantlyimprovedbythemodelofthisstudyascom-paredwithmodelsthatneglectaerosol-phasereactionsofgaseousDMSoxidationproducts.TheMSAproductionappearstoincreaseinthepresenceofisoprene.TheIRRanalysisinthemodelsuggeststhatthepresenceofisopreneincreasesNOxcyclesduringtheDMSphotooxidation.Subsequently,thereactionofDMSwithO3Pisenhanced,eventuallycausinghigheryieldsofMSAandH2SO4throughgas-phasereactions.Withgreaterpro-ductionofMSAandH2SO4inthepresenceofhighconcen-trationsofisoprene,theaerosol-phasereactionsofDMSOandMSIAwerealsoenhanced,inturnproducingmoreMSA.However,intheambientrelevantconcentrationsthemodelpredictionsuggeststhatisoprenemayincreasetheyieldsofMSAandH2SO4onlyinthebeginningthroughthereactionofDMSwithO3P,butdecreasethemlater.ForverylowconcentrationofDMS,theCH3OSOradicalproducesSO2insteadofreactingwithatmosphericoxidantsandform-ingMSAandH2SO4.Withoutaerosol-phasereactions,thegapbetweentheob-servedMSAconcentrationsandthepredictedconcentrationsbecomelargerastheMSAconcentrationincreases,asshowninDMSO-1inFig.2andDMSO-5inFig.S3.ThistendencyevincesthattheproductionofMSAdependsontheavail-ableaerosolmass,whichdirectlyinuencesaerosol-phasechemistryofbothDMSOanditsoxidationproductssuchasDMSO2andMSIA.TheunderpredictionofbothMSAandH2SO4isalsoobservedintheDMS-isoprenesystemevenwithaerosol-phasechemistryinthekineticmodel.Theun-derpredictionofMSAappearstobegreaterwhenisopreneconcentrationsarehigher.Suchdeviationmightbecausedbythelackofaerosol-phasechemistryofDMSoxidationproductsonisopreneSOA,suggestingthatgas-phasemech-anismsalonecannotcorrectlypredicttheformationofMSA.ForthemixtureofDMSandisoprene,isopreneSOAmod-iesthechemicalandphysicalpropertiesofDMSaerosolandtherefore,inuencesaerosol-phasereactionsofDMSox-idationproducts.Meanwhile,theDMSacidicproductssuchasMSAandH2SO4areabletocatalyzeaerosolphasere-actionsofisopreneoxidationproductsincreasingSOApro-duction Jangetal. 2002 .ToimprovetheDMSoxidationmodel,thesynergeticinteractionbetweenDMSoxidationproductsandisopreneSOAshouldbediscoveredinthefu-ture.InadditiontotheSOAissue,Zhuetal. 2006 indi-catedthattheOHradicalreactionwithMSAconsumesal-most20%ofMSAandproducesabout8%ofH2SO4within3daysundertypicalmarineatmosphericconditions.Inthisstudy,duetotheshortduration3hours,theMSAdecaymightbeinsignicant.However,thisshouldbeconsideredwhenthemodelisappliedtothereactionsintheambientair.SimilartotheMSAproductionthroughaerosol-phasereac-tionsofDMSO,SO2canbeoxidizedinaerosolphasebutwillnotbesignicantbecauseofitslowreactivitywithox-idantse.g.,OHradical.However,intheambientair,theaerosol-phaseproductionofH2SO4throughSO2reactionsonaerosolshouldbeconsiderableespeciallyinthepresenceofatmosphericcatalystssuchasironions Freiberg 1974 Supplementarymaterialrelatedtothisarticleisavailableonlineat: http://www.atmos-chem-phys.net/12/1/2012/acp-12-1-2012-supplement.pdf Acknowledgements. ThisworkwassupportedbygrantsfromtheNationalScienceFoundationATM-0852747andtheAlumniScholarshipfromtheUniversityofFlorida.PublicationofthisarticlewasfundedinpartbytheUniversityofFloridaOpen-AccessPublishingFund.Editedby:D.KnopfReferences Atkinson,R.,Baulch,D.L.,Cox,R.A.,Hampson,R.F.,Kerr,J.A.,andTroe,J.:EvaluatedKineticandPhotochemicalDataforAtmosphericChemistry.3.IupacSubcommitteeonGasKineticDataEvaluationforAtmosphericChemistry,J.Phys.Chem.Ref.Data.,18,881,1989. Atkinson,R.,Baulch,D.L.,Cox,R.A.,Hampson,R.F.,Kerr,J.A.,Rossi,M.J.,andTroe,J.:Evaluatedkineticandphotochemicaldataforatmosphericchemistry:SupplementVI-IUPACsub-committeeongaskineticdataevaluationforatmosphericchem-istry,J.Phys.Chem.Ref.Data,26,1329,1997. Balla,R.J.andHeicklen,J.:OxidationofSulfurCom-pounds.2.ThermalReactionsofNO2withAliphaticSulfur-Compounds,J.Phys.Chem.-US,88,6314,1984. Ballesteros,B.,Jensen,N.R.,andHjorth,J.:FT-IRstudyofthekineticsandproductsofthereactionsofdimethylsulphide,dimethylsulphoxideanddimethylsulphonewithBrandBrO,J.Atmos.Chem.,43,135,2002. www.atmos-chem-phys.net/12/1/2012/Atmos.Chem.Phys.,12,1 13 ,2012

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