环境化学英文课件6

ParticlesandCloudsCloudalbedoforcing:CoolingTheshortwaveraysfromtheSunarescatteredinacloud;manyoftheraysreturntospace.Theresulting"cloudalbedoforcing”,takenbyitself,tendstocauseacoolingoftheEarth.CloudGreenhouseForcing:WarmingLongwaveradiationWhenacloudabsorbslongwaveradiationemittedbytheEarth'ssurface,thecloudre-emitsaportionoftheenergytospaceandaportionbacktowardthesurface.Thisprocessiscalled"cloudgreenhouseforcing"and,takenbyitself,tendstocauseaheatingor"positiveforcing"oftheEarth'sclimate.OveralleffectofallcloudsCloudalbedoforcingcoolingCloudgreenhouseforcingwarmingTheoveralleffectofallcloudstogetheristhattheEarth'ssurfaceiscoolerthanitwouldbeiftheatmospherehadnocloudsThedominatefactorintheglobalalbedoisclouds.Aerosol:DefinitionAerosolisasuspensionofsolidorliquidparticlesinagas.Atmosphericaerosolsconsistofsmallparticlesofliquidandsolidmaterialsuspendedintheair.Bioaerosol:Anaerosolofbiologicalorigin.(Examples:viruses,bacteria,fungi,spores,andpollens.)Aerosolsizesareusuallymeasuredintheunitofmicrometer(mm)1mm=10–6m1mm=104angstrom(Å)TypicalParticleDiameters(mm)Photochemicalaerosols0.01-1Tobaccosmoke0.25Coalflyash1-50Flourdust15-20Pollens15-70Humanhair:~25-100mmExampleimagesofatmosphericparticlesSource:http://www.mpch-mainz.mpg.de/~kosmo/AerosolsourcesAerosolsourcesWindblowndustfromDesertSulfateaerosolfromvolcanoeruption,fuelcombustionandmicrobialactivities.SeasaltaerosolfromseasprayandbubbleburstingSootfromfuelcombustionSecondaryorganicaerosolfromvolatileorganiccompoundsAerosolRadiativeForcing:directeffectTheeffectofaerosolontheenergyfluxoftheatmospheredependsonparticlesizeandcomposition.Darkparticles(soot–containing)tendtoabsorblight,thuswarmingEarth’satmosphere.Smallparticlestendtoscatterlight,thusincreasingthealbedooftheatmosphere.Aerosolandcloudcondensationnuclei(CCN)CloudCondensationNuclei(CCN)areparticlesthatcanbecomeactivatedtogrowtofogorclouddropletsinthepresenceofasupersaturationofwatervapor.IftheEarth’satmosphereweretotallydevoidofparticles,cloudscouldnotform.Aerosolradiativeforcing:indirecteffectAnincreaseinthenumberofatmosphericparticleswouldincreasethenumberofcloudcondensationnuclei,thereforemorecloudcoverandhigheralbedoShiptrackingphenomenonVolcanoesandclimatechangeLargevolcanoeruptionsprovidedramaticevidenceoftheabilityofaerosolstoaffectglobalclimate.Mt.Pinatuboeruptionmade1992thecoolestyearsince1986Redline:modeledtemperaturechangesBlueline:temperaturechangesobservedfrommeteorologicalgroundstationsVolcanicCoolingLargevolcaniceruptionscancooltheEarthbyincreasingthealbedo.Calculatetheexpectedtemperaturechangeifthealbedoincreasesfrom30to30.5percent.ComparethisestimatewiththetemperaturerecordaftertheMt.Pinatuboeruption.(Textbook,pp150).1816-theyearwithoutasummerIn1815,TamborainIndonesiaexplodedandthevolcanodustblanketedtheNorthernHemisphere.Thefollowingyear,1816,dailyminimumtemperatureswereabnormallylowinthenorthernhemispherefromlatespringtoearlyautumn.Faminewaswidespreadbecauseofcropfailures.Anestimated82,000werekilledindirectlybytheeruptionbystarvation,disease,andhunger.SulfateaerosolformationfromvolcanoeruptionsLargeamountofSO2isinjectedintotheatmospherefromtheforceofthevolcanoeruption.SO2canbeconvertedtosulfateingasandaqueousphase.Ingas-phaseSO2+.OH+MHOSO2.+MHOSO2.+O2HO2.+SO3SO3+H2O+MH2SO4+MSulfateaerosolformationfromvolcanoeruptions(Continued)Inaqueousphase,dissolvedSO2isoxidizedtosulfatebyO3 (dominantpathwaywhenpH>5)H2O2 (dominantpathwaywhenpH<5)organicperoxidesO2catalyzedbyironandmanganeseTheoxidationofSO2(aq)byH2O2proceedsasfollows:HSO3-+H2O2SO2OOH-+H2OSO2OOH-+H+H2SO4SulfateformationfrombiogenicgasesDimethylsulfide(DMS):CH3SCH3MarineoriginProducedinplanktonbytheenzymaticcleavageofdimethylsulfonopropionate,acompoundthathelpplanktonachieveosmoticbalanceinthesaltyoceanwater.OxidationofDMSSO2sulfateH2STerrestrialoriginProducedbysulfate-reducingbacteria.Example:KuwaitOilFires

Airtemperaturesbelowtheplumeswerereportedtobeabout7oClowerthaninadjacentareaswithoutsmoke.ColdestMayin35years.Averagetemperatureswereabout4oClowerthannormal.AerosolEffectsonClimateDirectEffectsAerosolsscatterandabsorbvisibleandinfraredradiationOveralleffect:coolingLig