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1、Lesson14AirpollutionAirpollutionisthehumanintroductionintotheatmosphereofchemicals,particulatematter,orbiologicalmaterialsthatcauseharmordiscomforttohumansorotherlivingorganisms,ordamagesthenaturalenvironment.Airpollutioncausesdeathsandrespiratorydisease.Airpollutionisoftenidentifiedwi
2、thmajorstationarysources,butthegreatestsourceofemissionsismobilesources,mainlyautomobiles.Gasessuchascarbondioxide,whichcontributetoglobalwarming,haverecentlygainedrecognitionaspollutantsbyclimatescientists,whiletheyalsorecognizethatcarbondioxideisessentialforplantlifethroughphotosynth
3、esis.Theatmosphereisacomplex，dynamicnaturalgaseoussystemthatisessentialtosupportlifeonplanetEarth.StratosphericozonedepletionduetoairpollutionhaslongbeenrecognizedasathreattohumanhealthaswellastotheEarth'secosystems.Anairpollutantisknownasasubstanceintheairthatcancauseharmtohumansandth
4、eenvironment.Pollutantscanbeintheformofsolidparticles,liquiddroplets,orgases.Inaddition,theymaybenaturalorman-made.Pollutantscanbeclassifiedasprimaryorsecondary.Usually,primarypollutantsaredirectlyemittedfromaprocess,suchasashfromavolcaniceruption,thecarbonmonoxidegasfromamotorvehiclee
5、xhaustorsulfurdioxidereleasedfromfactories.Secondarypollutantsarenotemitteddirectly.Rather,theyformintheairwhenprimarypollutantsreactorinteract.Animportantexampleofasecondarypollutantisgroundlevelozone—oneofthemanysecondarypollutantsthatmakeupphotochemicalsmog.Notethatsomepollutantsmay
6、bebothprimaryandsecondary:thatis,theyarebothemitteddirectlyandformedfromotherprimarypollutants.Majorprimarypollutantsproducedbyhumanactivityinclude:●Sulfuroxides(SOx)especiallysulfurdioxide,achemicalcompoundwiththeformulaSO2.SO2isproducedbyvolcanoesandinvariousindustrialprocesses.Since
7、coalandpetroleumoftencontainsulfurcompounds,theircombustiongeneratessulfurdioxide.FurtheroxidationofSO2,usuallyinthepresenceofacatalystsuchasNO2,formsH2SO4,andthusacidrain.Thisisoneofthecausesforconcernovertheenvironmentalimpactoftheuseofthesefuelsaspowersources.●Nitrogenoxides(NOx)e
