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1、.1.有篇长阅读 老G改的那个污染汽油乙醇替代石油燃料环保的那篇1993年04AAlthough,recentyearshaveseensubstantialreductionsinnoxiouspollutantsfromindividualmotorvehicles,thenumberofsuchvehicleshasbeensteadilyincreasingconsequently,morethan100citiesintheUnitedStatesstillhavelevelsofcarbonmonoxide,particula
2、tematter(particulatematter:颗粒物质),andozone(generatedbyphotochemicalreactionswithhydrocarbons(hydrocarbon：n.烃,碳氢化合物)fromvehicleexhaust)thatexceedlegallyestablishedlimits.Thereisagrowingrealizationthattheonlyeffectivewaytoachievefurtherreductionsinvehicleemissions—shortof(sh
3、ortof:adv.缺乏,只要没有)amassiveshiftawayfrom(awayfrom:远离)theprivateautomobile—istoreplaceconventionaldieselfuelandgasolinewithcleaner-burningfuelssuchascompressednaturalgas,liquefiedpetroleumgas(liquefiedpetroleumgas:n.液化石油气acompressedgasthatconsistsofflammablehydrocarbons(asp
4、ropaneandbutane)andisusedespeciallyasfuelorasrawmaterialforchemicalsynthesis),ethanol,ormethanol.Allofthesealternativesarecarbon-basedfuelswhosemoleculesaresmallerandsimplerthanthoseofgasoline.Thesemoleculesburnmorecleanlythangasoline,inpartbecausetheyhavefewer,ifand,carb
5、on-carbonbonds,andthehydrocarbonstheydoemitarelesslikelytogenerateozone.Thecombustionoflargermolecules,whichhavemultiplecarbon-carbonbonds,involvesamorecomplexseriesofreactions.Thesereactionsincreasetheprobabilityofincompletecombustionandaremorelikelytoreleaseuncombusteda
6、ndphotochemicallyactivehydrocarboncompoundsintotheatmosphere.Ontheotherhand,alternativefuelsdohavedrawbacks.Compressednaturalgaswouldrequirethatvehicleshaveasetofheavyfueltanks—aseriousliabilityintermsofperformanceandfuelefficiency—andliquefiedpetroleumgasfacesfundamental
7、limitsonsupply.Ethanolandmethanol,ontheotherhand,haveimportantadvantagesoverothercarbon-basedalternativefuels:theyhaveahigherenergycontent(energycontent:能含量；内能)pervolumeandwouldrequireminimalchangesintheexistingnetworkfordistributingmotorfuel.Ethanoliscommonlyusedasagasol
8、inesupplement,butitiscurrentlyabouttwiceasexpensiveasmethanol,thelowcostofwhichisoneofitsattract
