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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,morethan100citiesintheUnitedStatesstillhavelevelsofcarbonmonoxi
2、de,particulatematter(particulatematter:颗粒物质),andozone(generatedbyphotochemicalreactionswithhydrocarbons(hydrocarbon：n.烃,碳氢化合物)fromvehicleexhaust)thatexceedlegallyestablishedlimits.Thereisagrowingrealizationthattheonlyeffectivewaytoachievefurtherreductionsinve
3、hicleemissions—shortof(shortof:adv.缺乏,只要没有)amassiveshiftawayfrom(awayfrom:远离)theprivateautomobile—istoreplaceconventionaldieselfuelandgasolinewithcleaner-burningfuelssuchascompressednaturalgas,liquefiedpetroleumgas(liquefiedpetroleumgas:n.液化石油气acompressedgast
4、hatconsistsofflammablehydrocarbons(aspropaneandbutane)andisusedespeciallyasfuelorasrawmaterialforchemicalsynthesis),ethanol,ormethanol.Allofthesealternativesarecarbon-basedfuelswhosemoleculesaresmallerandsimplerthanthoseofgasoline.Thesemoleculesburnmorecleanl
5、ythangasoline,inpartbecausetheyhavefewer,ifand,carbon-carbonbonds,andthehydrocarbonstheydoemitarelesslikelytogenerateozone.Thecombustionoflargermolecules,whichhavemultiplecarbon-carbonbonds,involvesamorecomplexseriesofreactions.Thesereactionsincreasetheprobab
6、ilityofincompletecombustionandaremorelikelytoreleaseuncombustedandphotochemicallyactivehydrocarboncompoundsintotheatmosphere.Ontheotherhand,alternativefuelsdohavedrawbacks.Compressednaturalgaswouldrequirethatvehicleshaveasetofheavyfueltanks—aseriousliabilityi
7、ntermsofperformanceandfuelefficiency—andliquefiedpetroleumgasfacesfundamentallimitsonsupply.Ethanolandmethanol,ontheotherhand,haveimportantadvantagesoverothercarbon-basedalternativefuels:theyhaveahigherenergycontent(energycontent:能含量；内能)pervolumeandwouldrequi
8、reminimalchangesintheexistingnetworkfordistributingmotorfuel.Ethanoliscommonlyusedasagasolinesupplement,butitiscurrentlyabouttwiceasexpensiveasmethanol,thelowcostofwhichisoneofitsattracti
