学位论文-—汽车专业 翻译 中英文（全）automobile emissions.doc

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1、Lesson6-AutomobileEmissionsTrafficJamBackgroundInformationEmissionsfromanindividualcararegenerallylow,relativetothesmokestackimagemanypeopleassociatewithairpollutionbutinnumerouscitiesacrossthecountry,thepersonalautomobileisthesinglegreatestpolluterwithemissio

2、nsfrommillionsofvehiclesontheroad.Drivingaprivatecarisprobablyatypicalcitizen’smost“polluting”dailyactivity.TheCleanAirActof1970gaveEPAbroadauthoritytoregulatemotorvehiclepollution,andtheagency’semissioncontrolpolicieshavebecomeprogressivelymorestringentsincet

3、heearly1970’s.EPAstandardsdictatehowmuchpollutionautosmayemitbutautomakersdecidehowtoachievethepollutionlimits.Theemissionreductionsofthe1970’scameaboutbecausefundamentalimprovementsinenginedesignplustheadditionofcharcoalcanisterstocollecthydrocarbonvaporsande

4、xhaustgasrecirculationvalvestoreducenitrogenoxides.Theadventof“firstgeneration”catalyticconvertersin1975significantlyreducedhydrocarbonandcarbonmonoxideemissions.Theuseofconvertersprovidedahugeindirectbenefitaswell.Theconvertersleadtothewidespreadintroductiono

5、funleadedgasolinebecauseleadinactivatesthecatalyst.Thisresultedindramaticreductionsinambientleadlevelsandalleviatedmanyseriousenvironmentalandhumanhealthconcernsassociatedwithleadpollution.Thenextmajormilestoneinvehicleemissioncontroltechnologycamein1980-81.In

6、responsetotighterstandards,manufacturersequippednewcarswithevenmoresophisticatedemissioncontrolsystems.Thesesystemsgenerallyincludea“three-way”catalyst,anon-boardcomputer,andanoxygensensor.Thisequipmenthelpsoptimizetheefficiencyofthecatalyticconverter.Provisio

7、nsofthe1990CleanAirActarefurtherreducingvehicleemissions.Mobilesourceprovisionsincludeeventightertailpipestandards,increaseddurability,improvedcontrolofevaporativeemissions,andcomputerizeddiagnosticsystemsthatidentifymalfunctioningemissioncontrols.Eventhoughef

8、fortsbygovernmentandindustryhavegreatlyreducedtypicalvehicleemissions,thenumberofmilesAmericansdrivehasmorethandoubledsince1970.Theincreaseintravelhasoffsetmuchoftheemissioncontrol