大氣環(huán)境化學(xué)

會計學(xué)1大氣環(huán)境化學(xué)ATMOSPHERESTRUCTURE&BULKCOMPOSITION

Pressureunits1atm=1.013x106gcm-1s-21mbar=103gcm-1s-21hPa=103gcm-1s-2IdealgaslawpV=RgTp=(RgT)/MaSource:EnvironmentalScience,Cunningham,P.W.andB.W.Saigo,2001第1頁/共35頁ATMOSPHERICTRANSPORTTIMESCALESSource:IntroductiontoAtmosphericChemistry,Jacob,D.J.,1999第2頁/共35頁

TYPICALATMOSPHERICCOMPOSITION(molefraction)

TypicalunitsNumberconcentration:moleculescm-3Mixingratio:ppm,ppb,ppt

MolecularweightofairMa=28.96gmole-1TracechemistryReactantsarepresentintraceamounts第3頁/共35頁OXIDIZINGNATUREOFTHEATMOSPHERE

Earth’satmosphereisoxidizingduetopresenceofO2SO2-->SO42-;CH4-->CO;CO-->CO2;NO2-->HNO3

RadicalsareoxidizingagentsintheatmosphereOHisthecleansingagentoftheatmosphereKeytounderstandingatmosphericoxidantchemistryUnderstandradicalcyclingbutradicalcycleisintimatelyconnectedtooxidantchemistryofothertracecompoundsincludingO3StartwithO3O3isimportantfromchemical,climate,andhealthperspectives第4頁/共35頁ATMOSPHERICO3–ABRIEFHISTORY

1840:Ozonediscoveredin1840byC.F.Sch?nbein–thoughtitwasmadeupofoxygenandhydrogen1848:Systematicmeasurementattempts–curiousity,growinginterestinenv.,healtheffects,‘economyofnature’1861:OdlingsuggestedthatozonewasO31930:ChemicalmechanismforO3layerpostulated1952:O3identifiedascomponentofchemicalsmogChristianFrederichSch?nbein第5頁/共35頁OZONEANDHEALTH

90%ofO3isinthestratosphere;O3layerwithmax~9ppmAbsorptionof=200-320nm(UV-BandUV-C)bystrat.O3Source:StratosphericOzone,NASA/GSFC第6頁/共35頁OZONEANDSTRATOSPHERICTEMPERATURE

LocalheatingofthestratosphereduetoUVabsorptionbyO3TroposphericO3isalsoanimportantgreenhousegasSource:StratosphericOzone,NASA/GSFCSource:EnvironmentalScience,Cunningham,P.W.andB.W.Saigo,2001第7頁/共35頁O3O(1D)O(3P)2OHSolarradiation,wavelength290-320nmH2OO2,N2O2OZONEANDATMOSPHERICCHEMISTRY

O3istheprimarysourceoftroposphericOHOHisatmospheric‘detergent’

第8頁/共35頁LATITUDINAL&TEMPORALVARIATIONOFTOTALO3

TotalO3inrangeof300-400DUPatternsduetostratosphericcirculationLowtotalO3athighsouthernlatinsouthernspringdueto‘ozonehole’Dobsonunits1DU=2.69x1016moleculesO3cm-2Source:StratosphericOzone,NASA/GSFC第9頁/共35頁STRATOSPHERICO3CHEMISTRY第10頁/共35頁THECHAPMANMECHANISMFORSTRATOSPHERICO3

CyclingbetweenO,O2,andO3

Source:StratosphericOzone,NASA/GSFC第11頁/共35頁MISSINGCHEMISTRYINCHAPMANMECHANISM

GlobalO3productionrate=5timesdestructionrateImbalancesuggestsoverest.ofprodn.orunderest.oflossO3productionwellconstrainedbygoodspectroscopicdataImpliesmissingchemicalsinksforOxReactionsofradicalswithOand/orO3

ButradicalswillalsobeconsumedbyreactionmeasuredcalculatedSource:StratosphericOzone,NASA/GSFC第12頁/共35頁CATALYTICOXDESTRUCTIONINTHESTRATOSPHERE

RadicalchainreactionsX+O3

XO+O2XO+OX+O2Net:O+O3

2O2‘X’inthestratosphereH,OH,NO,ClHOx,NOx,andClxHOx=H+OH+HO2NOx=NO+NO2Clx=Cl+ClOReservoirstieupactiveradicalse.g.ClO+NO2ClONO2

StratosphericClxprecursorsSource:StratosphericOzone,NASA/GSFC第13頁/共35頁ColumnO3(DU)

ANTARCTICTOTALOZONEDECREASE

DepletionoftotalcolumnO3startinginmid-tolate-70’sduringSHspringGas-phasechemistrypredictedsmallerdecreases¬overAntarcticaO3Source:StratosphericOzone,NASA/GSFCSource:Farmannetal.,Nature,v.315,May1985第14頁/共35頁

ALTITUDEDEPENDENCEOFANTARCTICO3DECREASE

Strongdepletionbetween12and20kmGasphasechemistrypredicteddecreasenear40kmSource:StratosphericOzone,NASA/GSFC第15頁/共35頁

TEMPORALDEPENDENCEOFANTARCTICO3DECREASE

DepletionbeginsaroundSep1.&minimumisreachedaroundOct1Source:NOAA/CMDL第16頁/共35頁

REACTIONSONPOLARSTRATOSPHERICCLOUDS

ConversionofinactiveCltoactiveClandremovalofNOxSource:StratosphericOzone,NASA/GSFC第17頁/共35頁ROLEOFMETEOROLOGYLowtemps.PSCformationreleaseofactiveClandremovalofNOxStrongvortexIsolatesairfrommid-lats.preventshighO3airinfluxFigureshowsstrongpolarvortex(asshownbysizeofwindvectors)&lowpolartemps.(asshownbycolors)atvariousaltitudesinthesouthernhemispherestratosphereSource:StratosphericOzone,NASA/GSFC第18頁/共35頁NORTHERNvsSOUTHERNHEMISPHEREO3TRENDS

Vortexnotasstrongandtemps.notaslowinNHSource:StratosphericOzone,NASA/GSFC第19頁/共35頁PROJECTEDCHANGESINSTRATOSPHERICClx

MontrealProtocolandsubsequentamendmentswillhavesignifcantimpactsonprojectedClxloadingofstratosphere(ppb)Source:StratosphericOzone,NASA/GSFC第20頁/共35頁

WMO1998ScientificAssessmentofOzoneDepletionOzonedepletionin2050wouldbeatleast50%atmidlatitudesintheNorthernHemisphereand70%atmidlatitudesintheSouthernHemisphere,about10timeslargerthantoday

SurfaceUV-Bradiationin2050wouldatleastdoubleatmidlatitudesintheNorthernHemisphereandquadrupleatmidlatitudesintheSouthernHemispherecomparedwithanunperturbedatmosphere.Thiscomparestothecurrentincreasesof5%and8%intheNorthernandSouthernHemispheres,respectively,since1980ESTIMATEDIMPACTSOFClxCONTROLS第21頁/共35頁TROPOSPHERICO3CHEMISTRYSource:EPA第22頁/共35頁

TroposphericO3generallylessthan100ppbawayfromurbanareasTROPOSPHERICO3Source:Wangetal.,1998第23頁/共35頁O3chemicalproductioninstratospherefollowedbydownwardtransporttothetroposphereO2O(3P)Solarradiation,(<240nm)O3O2Solarradiation(<320nm),MSTRATOSPHERICSOURCEOFTROPOSPHERICO3Strat.chem.destructionbyHOx,NOx,ClxTransporttotrop.第24頁/共35頁NO2NOorO3

OHHO2COO3O2solarradiation,O2Net:CO+2O2-->CO2+O3CatalyticroleofNOx(NO+NO2)inrecyclingHO2toOHCouplingbetweenOHandHO2(HOx)viaNOCOOXIDATIONCYCLE–O3PRODUCTIONCO2O3第25頁/共35頁NOorO3

OHHO2COO2Net:CO+O3-->CO2+O2ChemicalO3destructionCouplingbetweenOHandHO2(HOx)viaO3COOXIDATIONCYCLE–O3DESTRUCTIONCO2O32O2第26頁/共35頁O3+hvO2+O(1D)2.O(1D)+MO+M3.H2O+O(1D)2OH4.RH+OHRO2+H2O5.RO2+NORO+NO26.RO+O2R`CHO+HO27.HO2+NOOH+NO28.HO2+HO2H2O2+O29.OH+NO2+MHNO3+MSCHEMATICOFHYDROCARBONCHEMISRYO2Netrxns1-7:RH+4O2

R’CHO+2O3+H2OSource:IntroductiontoAtmosphericChemistry,Jacob,D.J.,1999canproducemoreO3第27頁/共35頁ROLEOFNOXINO3CHEMICALPRODUCTIONCyclingofHOx(OH+HO2)byNOxvs.radicalterminationreactionsToolittleNOx:Radicaltermination(e.g.HO2+HO2)ratherthanradicalcycling(e.g.HO2+NO)leadingtoO3chemicaldestructionToomuchNOx:Radicalterminationbyalternateroute(e.g.OH+NO2)aswellasshort-termO3destructionbyNO+O3-->NO2==>implicationsforO3peakdownwindofstrongNOXsources第28頁/共35頁NOx-ANDHYDROCARBON-LIMITEDREGIMESNOxlimitedHydrocarbonlimitedComplications:NaturalemissionsofhydrocarbonsareimportantTranportofpollutantsintoandoutofregionSource:IntroductiontoAtmosphericChemistry,Jacob,D.J.,1999第29頁/共35頁Questions: NOxorHCemissioncontrolsorcombination DegreeofemissioncontrolsUncertaintiesReliabilityofemissioninventories(e.g.naturalhydrocarboninventories)Reliabilityofairqualitymodels(e.g.localvstransportedNOx/HC/O3)

ISSUESINO3POLLUTIONCONTROL第30頁/共35頁1998MEASUREDSURFACEOZONECONCENTRATIONS2ndhighestdailymax1-hr(ppb)<6565-1241