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EnvironmentalImplicationofElectricVehiclesinChinaHONGHUO,*,QIANGZHANG,MICHAELQ.
WANG,§DAVIDG.
STREETS,|ANDKEBINHE*,⊥InstituteofEnergy,EnvironmentandEconomy,TsinghuaUniversity,Beijing100084,China,CenterforEarthSystemScience,TsinghuaUniversity,Beijing100084,China,CenterforTransportationResearch,ArgonneNationalLaboratory,9700SouthCassAvenue,Argonne,Illinois60439,DecisionandInformationSciencesDivision,ArgonneNationalLaboratory,9700SouthCassAvenue,Argonne,Illinois60439,andStateKeyJointLaboratoryofEnvironmentSimulationandPollutionControl,DepartmentofEnvironmentalScienceandEngineering,TsinghuaUniversity,Beijing100084,ChinaReceivedFebruary15,2010.
RevisedmanuscriptreceivedMay10,2010.
AcceptedMay11,2010.
Today,electricvehicles(EVs)arebeingproposedinChinaasoneofthepotentialoptionstoaddressthedramaticallyincreasingenergydemandfromon-roadtransport.
However,themassuseofEVscouldinvolvemultipleenvironmentalissues,becauseEVsuseelectricitythatisgeneratedprimarilyfromcoalinChina.
Weexaminedthefuel-cycleCO2,SO2,andNOxemissionsofEVsinChinainbothcurrent(2008)andfuture(2030)periodsandcomparedthemwiththoseofconventionalgasolinevehiclesandgasolinehybrids.
EVsdonotpromisemuchbenetinreducingCO2emissionscurrently,butgreaterCO2reductioncouldbeexpectedinfutureifcoalcombustiontechnologiesimproveandtheshareofnonfossilelectricityincreasessignicantly.
EVscouldincreaseSO2emissionsby3-10timesandalsodoubleNOxemissionscomparedtogasolinevehiclesifchargedusingthecurrentelectricitygrid.
Inthefuture,EVswouldbeabletoreachtheNOxemissionlevelofgasolinevehicleswithadvancedemissioncontroldevicesequippedinthermalpowerplantsbutstillincreaseSO2.
EVsdorepresentaneffectivesolutiontoissuesinChinasuchasoilshortage,butcriticalpolicysupportisurgentlyneededtoaddresstheenvironmentalissuescausedbytheuseofEVstomakeEVscompetitivewithothervehiclealternatives.
1.
IntroductionInordertocopewiththeoilsecurityissue,manycountriesworldwidearemakingsubstantialeffortstoreducethedependenceoftheirtransportationsectoronpetroleumresourcesandyetfulllthefueldemandofthetransport(1-3).
Chinafacesthesamechallengesasothercountries.
Sincethe1990s,Chinahasbeenexperiencingveryrapidgrowthinvehiclepopulation.
ThevehiclepopulationinChinawasabout63millionby2008,anditisprojectedtobe550-730millionby2050(4),38-83%higherthanthatoftheU.
S.
in2050(5).
Oneimportantquestionraisedishowtoaccom-modatethislargenumberofvehiclesintermsofenergysources.
TodayinChinaonefrequentlyproposedansweriselectricvehicles(EVs),whichcouldalleviatedependenceonpetroleumbyusingotherenergysourcessuchascoalandhydro.
Nowelectrictwo-wheelers(E-2Ws)andthree-wheelersareverypopularinChina.
SomeE-2Wmanufacturersarealreadyproducingthree-orfour-wheelfullyenclosedEVsusingthesamebatterytechnologyasE-2Ws(6).
Recently,China'slargestelectricityproviderannouncedtheconstruc-tionofchargingstationsforEVsinBeijing,Shanghai,andTianjin.
Also,thesuccessfuldemonstrationofEVsinBeijingduringtheOlympicGamesencouragedthepromotionofEVsinChina(7).
In2009,theChinesegovernmentinitiatedaprogramnamed"TencitiesandThousandVehicles",whichplanstoselectmorethan10citiesandtointroducemorethan1000HEVsandEVs(primarilyusedastaxisandbuses)ineachoftheselectedcitiesinthreeyearswithgovernmentsubsidy.
Thirteencitieswereselectedtoparticipateinthisprogram(seeFigure1forthelocationofthesecities),andthenumberofcitiesisincreasing.
Nowadays,ChinaisconsideredtobeaverypromisingmarketforEVs.
ThepowerofEVsiselectricityfromthegrid.
WhileEVscanofferattractivebenetsinpetroleumreduction,theycouldresultinmoreCO2emissionsthanconventionalvehiclesbecauseofthefactthatthemajorityofelectricityisgeneratedfromcoalinChina.
Anotherconcernassoci-atedwithEVsisthattheycouldincreaseemissionsofcriteriapollutantslikeSO2andNOxbecausepowerplantsarebelievedtobethelargestcontributortoChina'sSO2andNOxemissions(8).
Inviewofthis,weevaluatetheenvironmentalimpactsofEVsbyexaminingtheirpotentialCO2,SO2,andNOxemissionsinChinafromafuel-cyclepointofviewandcomparingthemwiththoseofconventionalgasolineinternalcombustionenginevehicles(ICEVs)andgasolinehybridelectricvehicles(HEVs)onaper-kilometerbasis.
Chinaisinaperiodofrapidchangeincompositionandcombustiontechnologiesofpowerplants,soweexaminetwotimepoints-current(2008)andfuture(2030).
TheGREET(Greenhousegases,RegulatedEmissions,andEnergyuseinTransportation)model(9),whichisdevel-opedbyArgonneNationalLaboratory,isadjustedwithdataforChinaandemployedforthisworktosimulatethefuel-cycleemissionsofthevehicles.
2.
GenerationMixCO2emissionsofEVsaredependentontheCO2-intensityofthegenerationmixforchargingEVs,andtheirSO2andNOxemissionsdependonnotonlythegenerationmixbutalsotheemissioncontroltechnologiesinthermalpowerplants.
Chinaconsistsofsixlargeinterprovincialpowergrids,whicharenamedfortheregionstheyserve:NortheastChina,NorthChina,CentralChina,EastChina,NorthwestChina,andSouthChina.
Thesixgridsarenotstrictlyindependent,asonegridcanbuypowerfromanothergridifneeded.
Figure1presentsthegenerationmixofthesesixpowergridsin2008(10).
CoalandhydroarethetwomajorenergysourcesofpowergenerationinChina,andthesplitbetweenthemvariesbyregion.
Coal-basedpowerdominatesintheNortheastandNorthgenerationmixes,withaproportionashighas95-98%.
TheNorthwest,Central,andSouthmixes*Correspondingauthore-mail:hhuo@tsinghua.
edu.
cn(H.
H.
),hekb@tsinghua.
edu.
cn(K.
H.
).
InstituteofEnergy,EnvironmentandEconomy,TsinghuaUniversity.
CenterforEarthSystemScience,TsinghuaUniversity.
§CenterforTransportationResearch,ArgonneNationalLaboratory.
|DecisionandInformationSciencesDivision,ArgonneNationalLaboratory.
⊥DepartmentofEnvironmentalScienceandEngineering,Tsin-ghuaUniversity.
Environ.
Sci.
Technol.
2010,44,4856–486148569ENVIRONMENTALSCIENCE&TECHNOLOGY/VOL.
44,NO.
13,201010.
1021/es100520c2010AmericanChemicalSocietyPublishedonWeb05/24/2010consistofmorethan22%hydropower,althoughcoalisstillthemajority.
TheSouthandEastgridsalsohave5%nuclearpower.
IntheU.
S.
,theelectricityconsumptionhasremainedstableinrecentdecades.
TheannualincreaserateofelectricityconsumptionintheU.
S.
was0.
5%during2000and2009andisprojectedbytheU.
S.
EnergyInformationAdministration(EIA)tobe0.
8%during2005and2035(11).
U.
S.
studieshavearguedthattheincreasingpenetrationofEVs(orplug-inhybrids)mayrequireadditionalnewpowercapacity,andtheenergyandenvironmentalimpactsofEVsshouldbeevaluatedbasedonthemarginalgenerationmix(12-14),whichisreasonablebecauseEVswillbetheprimaryreasonforthenewcapacity.
ButitisdifferentforthecaseofChina.
TheannualincreaserateofelectricityconsumptioninChinawas13.
5%during2000and2007(15)andisprojectedtobe5%during2010and2030(16).
ThegrowthofgenerationcapacityinChinaisdrivenbytheincreasingelectricitydemandforindustrial,residential,commercial,andtrans-portationsectors(16-18).
ThepotentialgrowthofEVsisoneofthedrivingforcesinChina,butitwillnotbestrongerthanthegrowthinothersectors.
BasedonsomeprojectionsforChinesenationalelectricitysupply(16-18)(EVs'potentialdemandwasnottakenintoaccountintheseprojections),weestimatethatthesparecapacityfromnewlyaddedplantsshouldalwaysbeabletofulllthenewdemandfromEVsfornowandthefuture(seeTable1)(10,14,16-22),whichmeansthatEVsinChinawillnotbeabletocausemajorchangeinpowergenerationcapacityevenwiththemostaggressivescenarioofalllight-dutypassengervehiclesonroadasEVsby2030(whichisfarfrompossible),andthuswillnotproducemarginaleffectsonpowergenerationcapacity.
Inthiswork,therefore,weestimateEVemissionsonthebasisoftheaveragegenerationmixratherthanthemarginalgenerationmix.
WithrespecttoChina'spotentialnewplantsbuiltinthefuture,sinceChinahaslimitedresourcesofoilandnaturalgas,themajorfossilfuelusedinChina'snewplantswillstillbecoal.
Inaddition,Chinaisplanningtoenhancethefractionofnonfossilgeneratingcapacitybyexpandinghydroandnuclearpoweranddevelopingnewplantsbasedonrenew-ableenergyresourcessuchaswindandsolar.
Obviously,thefractionofcoal-basedelectricityisacriticalparameterforevaluatingtheenvironmentalimpactsofEVs.
NumerousstudiesworldwidehavemadeprojectionsofthefutureoptionsforpowersupplyinChina.
EIAandtheInternationalEnergyAgency(IEA)projectedthatcoalwouldremainthepredominantfuelingeneration,and78-81%ofelectricityusedwouldbedrawnfromcoalby2030(17,18).
Domesticinstitutesaremoreoptimisticonthisissue,andtheyprojectthattheshareofcoalpowercouldbereducedto72%by2030(16)oranevenmoreambitioustarget-65%by2020(23).
CO2Emissions.
Theenergyefciencyofcoal-redpowerplantsinChinaiscurrentlyabout32-34%(16,24).
WeestimatetheCO2emissionrateofcoal-redpowerplantstobe1002gCO2/outlet-kWh,accordingtothelowheatingvaluesandcarboncontentofcoal,theproportionofeachtypeofcoalusedinpowergeneration,andtheelectricaltransmissionlosses(25-27),asshowninTableS1(where"S"referstotheSupportingInformation).
Weassumethatthecoalcompositionwouldbeunchangedinthefuture.
TherearenoreportsavailableonHEVs'orEVs'on-roadenergyefcienciesinChina,soweadoptedtheratiosoffuelefciencyvaluesofHEVsandEVstothoseofconventionalvehiclesintheGREETmodelinordertocomparethethreetypesofvehiclesonthebasisofthesameweightanddrivingconditions.
ThefuelconsumptionratesofEVs,ICEVs,andHEVsarepresentedinTable2(28,29).
Thedensityofgasolineis0.
732L/kg,anditscarbonratiois85.
5%(30).
TheGREETmodelshowsthatpowergenerationisresponsiblefor99%oftotalfuel-cycleCO2emissionsofEVspoweredbycoal-basedelectricity,suggestingthatpowergenerationisbyfarthedominantcontributortoCO2emissionsofEVs.
Figure2presentsthecurrentfuel-cycleCO2emissionsofEVspoweredbythesixregionalgridsandcoal-basedelectricityaswellastheCO2emissionsofgasolineICEsandHEVs.
Asshown,theCO2emissionsofEVsvarysignicantlybyregionbecauseofthedifferentregionalgenerationmixes.
EVspoweredbycoal-basedelectricitycouldincreaseCO2emissionsby7.
3%comparedtogasolineICEVs.
Conse-quently,EVsintheregionswherecoalcontributesahighproportionofpowergeneration(theNortheast,North,andEastregions)showverylimitedbenetinCO2reductionorcouldevenincreaseCO2emissions(suchasintheNorthregionwhereBeijingislocated),comparedtoICEVs.
However,inregionsthatpossessabout35%nonfossilelectricity(theSouthregions),EVscouldhavethesameCO2emissionlevelasgasolineHEVs,whichis30%lowerthangasolineICEVs.
So,thechoiceoflocationforusingEVscouldsignicantlyaffecttheCO2reductionbenet,frompositivetonegative.
Inthissense,theregionswithsmallerfractionsofcoal-basedelectricityshouldbethepriorityEVmarkets,suchastheSouth,Central,andNorthwestregions.
Forexample,ofthecitiesthatarechosenforthe"TenCitiesandThousandVehicles"Program(seeFigure1),EVsareagoodchoiceforChongqing(Central)andShenzhen(South),butFIGURE1.
Generationmixofthesixinterprovincialpowergridsin2008.
VOL.
44,NO.
13,2010/ENVIRONMENTALSCIENCE&TECHNOLOGY94857HEVswouldbeabetterchoicethanEVsforBeijing(North)andShanghai(East)intermsofCO2emissionreduction.
Chinaisplanningtodecreasethecarbonintensityofelectricitygenerationbyincreasingtheshareofnonfossilpowercapacity,andthereforeEVscouldbeexpectedtooffergreaterCO2savingsinthelongrun.
Figure3projectstheCO2emissionsofEVsasafunctionofthefractionofcoal-basedelectricity.
Theenergyefciencyofcoal-redpowerplantsisassumedtoriseto40%in2030(16).
Thefuelconsumptionratesofthethreetypesofvehiclesarealsoassumedtoimproveby2030(seeTable2).
AsshowninFigure3,thetheoreticalCO2breakevenpointbetweenEVsandICEVsis87%coalpower,whichmeansthatEVswouldhaveaCO2-reductionadvantageovergasolineICEVsifthecoalfractionisbelow87%.
The78-81%coalfractionsprojectedbyEIAandIEA(17,18)translatetoaCO2reductionof10%comparedtoICEVs.
UnderthemoreaggressiveprojectionsmadebyChineseinstitutes(65-72%)(16,23),theCO2emissionsofEVsare18-25%lowerthanICEVs,but7-18%higherthanHEVs.
Withtherightlocationschosen,theCO2reduction-benetofEVswouldbelarger.
Forinstance,theNorthwest,Central,andSouthregions,whichhaveplentyofhydroandwindresources,arethekeyregionstodevelopnonfossilpowerinChina.
Iftheirnonfossilelectricitysharereaches50%by2030,EVsoperatedintheseregionscouldachieveaveryimpressiveCO2reductionof18%comparedtoHEVs.
SincegasolineHEVscombustpetroleum-basedfuel,EVswouldbemoreattractivethanHEVswithalmostzeropetroleumuseandlowerCO2emissions.
AsshowninFigure3,thebenetcouldbeenlargedbyhigherenergyefciencyofpowerplants.
Onepercentilepointimprovementinenergyefciencywillbring2-5%moreCO2reductioncomparedtoHEVs.
Carboncaptureandsequestration(CCS)technologiescouldhelptoearnmorecarboncreditsforEVs,buttheyaresubjecttomanytechnicaluncertainties.
SO2Emissions.
Powerplantscontributemorethan97%offuel-cycleSO2emissionsofEVschargedwithcoal-basedelectricityaccordingtotheresultsfromGREET.
Thesulfurcontentofcoalandthepenetrationofue-gasdesulfurization(FGD)systemsaretwoimportantfactorsinuencingSO2emissionsfromcoal-redpowerplants.
ThesulfurcontentvariessignicantlyacrossregionsinChina,fromaslowas4.
2g/kgofcoalinthenortheastregiontoashighas14.
7g/kginthecentralregion(31)(seeTableS2).
FGDistypicallyabletoremove85%ofsulfuremissions.
Allunitsbuiltafter2004andalargefractionofexistingonesarerequiredtobeinstalledwithFGDunderChineselaw.
In2005,thecapacityofunitswithFGDwasonly10%ofthetotalcapacityofcoal-redplants(32).
WiththeaggressivetargetsetbytheChinesegovernmenttoreducenationalSO2emissionsby10%from2005to2010,theFGDpenetrationinthepowersectorisrisingrapidly,anditwasreportedtobe60%bytheendof2008(32).
TableS2providesFGDpenetrationestimatesforthesixregionsinChinain2008(32).
Weassumethatallcoal-redpowerplantswouldbeinstalledwithFGDby2030.
CoalwashingisanothertechnologythatcanreduceSO2emissionsby40%,butitisnotwidelyappliedinChinayet.
Thecurrentfractionofwashedcoalusedinpowergenerationisabout2.
5%inChina(15).
Theshareofcoal-basedelectricityinthesixregionalgridswasassumedtorangefrom50%to80%in2030,basedonthediscussionabove.
Duringrecentyears,thesulfurcontentregulationforvehicularfuelshadlaggedbehindthevehicleemissionstandardsinChina.
Thesulfurcontentofgasolinewas500ppminChina(33)exceptinafewlargecities(forexample,thesulfurcontentofgasolineinBeijingwas50ppmafter2008).
However,Chinastartedtoremedythisproblem.
Chinajustissuedanewregulationtorequirethesulfurcontentofgasolinetobebelow150ppm(theEuroIIIfuelstandard)bytheendof2009.
TheEuroVemissionstandardisexpectedtobeimplementedwithin10yearsinChina,soweassumethatthesulfurcontentwoulddecreaseto10ppm(theEuroVfuelstandard)nationwideby2030(seeTable2).
AccordingtotheGREETresult,theshareofvehicleSO2emissionsoutoftotalfuel-cycleemissionsofICEVsandHEVsdecreasesfrom33%to2%asthesulfurcontentofgasolinedeclinesfrom500ppmto10ppm.
Figure4illustratesthefuel-cycleSO2emissionsofEVsunderthesixregionalmixes,comparedtothoseofgasolineICEVsandHEVs.
Asshown,poweredbythecurrentelectricitymix,EVscouldcauseasignicantincreaseinSO2emissionsby3-6timesrelativetoICEVsand5-10timesrelativetoHEVs.
GasolinevehicleexhaustscontributeverylittletototalnationalSO2emission(0.
2%in2006)(8),butiftheyarereplacedbyEVs,thecontributionwouldriseto2-4%(theSO2emissionsofEVsare9-18timestheemissionsofICEVsatvehicleoperationstage).
EVswillposeanewchallengetoChina'stargetofcontrollingthetotalamountofSO2emissions.
Inthefuture,evenwithmoreadvancedcombus-tiontechnologiesand100%FGDpenetration,theSO2emissionsofEVswouldstillbe1.
3-5timestheemissionsofICEVsand3-7timestheemissionsofHEVs.
Evenwithanadditional100%coalwashing,whichisinfeasibleinpractice,itisnotpossibletobringtheSO2emissionsofEVsdowntothelevelofICEVsandHEVsformostregionsinChina.
NOxEmissions.
NOxemissionratesincoal-redpowerplantsvarybyboilersize,levelofNOxcontroltechnology,andcoalquality.
TheaverageNOxemissionfactorsofcoal-redpowerplantsinChinadeclinedgraduallyfrom8.
9g/kgofcoalin1995to7.
4g/kgofcoalin2004asaresultoftheincreasedshareoflargeboilersandthespreadoflow-NOxburner(LNB)technology(26).
TheNOxremovalefciencyofLNBwasreportedtobe30%(34).
TheLNB-installedunitsTABLE1.
NumberofEVsThatCouldBeSupportedbytheGenerationCapacity20082030totalgenerationcapacity(GW)a7931500-1800usablecapacityforchargingEVs(GW)b4075-90energyefciencyofEVs(kWh/100km)c18-2512-20kilometerstraveledperyear18,000d12,000emaximumnumberofEVs(million)77-107273-548numberoflightpassengervehicles(million)f30186-217aCurrentcapacityvalueisfromref10,futurevalueswereprojectedbyrefs16-18.
bIdeally,rechargingofEVsshouldtakeplaceatnight-time.
Stephanetal.
estimatedthatnight-timesparecapacityis9-20%ofnetgenerationforchargingplug-inhybridsintheU.
S(14),andthisvaluecouldbelargerforChinabecausethepowergridhaslargerpeak-to-valleydifferences(19).
Conservatively,5%oftotalgenerationcapacityisassumedasthemaximumthatEVscouldutilizeinChina.
cEstimatedbyauthorsbasedonthecommercialreportsonperformanceofcurrentEVs.
TherangesrepresentthepossiblemaximumandminimumfueleconomyvaluesofallsizesofEVsinChinatoestimatehowmanyelectricvehiclescouldbesupportedbynight-timesparecapacity.
dTheassumptionismadeonthebasisofsurveyresultsreportedinref20.
eAccordingtoWangetal.
(21),thelevelofvehicleuseinChinain2030wouldbethesameasthecurrentlevelinEuropeancountries.
Vehicleusecouldbereducedinthefuture,becauseChinaisinaperiodofrapidgrowthinvehiclestock,andwhenpeopleownmorecars,eachindividualcarwouldbeusedlessintensively.
Pleaserefertoref21foradetailedexplanationforthisassumption.
fCurrentvaluewasprovidedbyref22;futurevalueswereprojectedbyref21.
48589ENVIRONMENTALSCIENCE&TECHNOLOGY/VOL.
44,NO.
13,2010accountedfor62%ofthetotalcapacityin2005,anditwasestimatedtoincreaseto77%by2010(35).
AsnewplantsarerequiredtoinstallLNB,theLNBpenetrationislikelytoreach90%orevenmoreby2030,andbythen,theNOxemissionfactorofcoal-redpowerplantscouldbeaslowas5g/kg.
Advancedtechnologiessuchasselectivecatalyticreduction(SCR)coulddecreaseNOxemissionsevenmoresignicantly.
Atpresent,thepenetrationrateofSCRinChinawasestimatedtobelowerthan10%(34).
TheremovalefciencyofSCRvariesfrom40%to90%inChina(34,36).
Inthiswork,weassumethattheremovalefciencyofSCRcouldreach70%-90%,andforthepurposeofsensitivityanalysis,100%removalefciencyofSCRforNOxisalsotakenintoconsiderationasaboundingcase.
ChinaisimplementingtheEuroIIIvehicleemissionstandardnationwide(exceptforsomelargecitieswhereEuroIVisalreadyineffect,suchasBeijing),andtheEuroIVandVstandardsareexpectedtobeinplacewithin10years.
By2030,gasolinevehiclesinChinawouldhavealreadymetEuroVIorevenstricterstandards.
Table2showstheemissionfactorsofgasolinevehiclesundertheEuroIII,IV,andV/VIstandards.
TableS3summarizestheadjustedparametersintheGREETmodelandotherkeyvariables.
Figure5presentsthecurrentfuel-cycleNOxemissionsofEVs,andthefutureemissionsrelatedtothepenetrationofSCRunderthethreegenerationmixscenarios,inwhichthesharesofcoalplantsare80%,65%,and50%,respectively.
Asshown,ifchargedbythecurrentelectricitymix,EVswoulddoubletheNOxemissionsofEuroIIIgasolinevehicles.
By2030,EVswillstillincreaseNOxemissionsby16-86%comparedtoEuroVgasolinevehiclesiftheSCRpenetrationiszero.
IftheapplicationratioofSCRreaches20%,EVschargedbythegenerationgridwith50%coal-basedelectricityTABLE2.
AssumptionsAssociatedwithFuels,FuelEfficiency,andEmissionFactorsofVehiclesgasolineICEVsgasolineHEVsEVsfuelconsumptionrates20088L/100km(28)5.
6L/100kmb24kWh/100kmb20305.
5L/100kma3.
9L/100kmb20kWh/100kmcsulfurcontentofgasoline,ppm2008500500-20301010-NOxemissionfactorsd,g/kmEuroIII0.
15-EuroIV0.
08-EuroV/VI0.
06-aFuturefueleconomyofICEVsisestimatedonthebasisofpolicytendencyinChina.
bFueleconomyvaluesofHEVsandEVsarecalculatedbyusingthefueleconomyratiosofHEVsandEVstoICEVsintheGREETmodel.
Thepossibleincreasedcongestioninthefuturewouldaffectthefueleconomyofthethreevehicletechnologiesindifferentways,butthedifferenceintheimpactsofpotentialcongestionontheirfueleconomyisverysmall(29)andthusisneglectedinthiswork.
cTheimprovementinfueleconomyofEVsinfuturereferstotheestimationintheGREETmodel.
dHereweusedthestandardlimitvaluesinsteadofon-roademissionfactors.
Accordingtotheon-boardvehicleemissionmeasurementsconductedbyTsinghuaUniversityduring2008-2009(unpublisheddata),theon-roadNOxemissionfactorofEuroIIIcarswas0.
11(0.
05g/km,whichisclosetothestandardlimitvalues.
FIGURE2.
Fuel-cycleCO2emissionsofEVswiththecurrentelectricitygenerationmixinChina.
FIGURE3.
Futurefuel-cycleCO2emissionsofEVsasafunctionofthefractionofcoal-basedelectricity.
FIGURE4.
Fuel-cycleSO2emissionsofEVscomparedtothoseofgasolineICEVsandHEVsinChina.
VOL.
44,NO.
13,2010/ENVIRONMENTALSCIENCE&TECHNOLOGY94859couldhavelowerNOxemissionsthangasolinevehicles.
EVschargedbyhighercoal-intensitygenerationgridswouldrequirehigherSCRpenetration,e.
g.
,electricitywith80%coalwillneedatleast44%SCRpenetration.
ThewidespreadapplicationofSCRwillbethekeyforEVstocompetewithgasolinevehiclesintermsofNOxemissions.
ImplicationsforEVs.
EVsdorepresentaverypromisingsolutiontoenergyissuesduetotheirsolidmeritsinsubstitutingforpetroleumfuels.
Butfornowthehighpollutionlevelsofcoal-redpowerplantswilltradeoffEVs'potentialenergybenetsinChina.
NotethattheemissionsassociatedwiththeconstructionofEVrecharginginfra-structurewerenottakenintoconsiderationinthiscalculation,whichcouldmakeEVsevenmoreunfavorableascomparedtoICEVsandHEVs.
Inaddition,otherenvironmentalimpactsassociatedwithcoal-redpowerplants,suchasmercuryemissions(byaroughestimation,EVscouldcause0.
01mgofmercuryemissionsforeverykilometerdriven)(37),maybecomeenvironmentalconcernsforEVstoo.
Chinaisexperiencingexplosivegrowthinitsvehiclepopulation,anditisprojectedtoexceedtheU.
S.
within20years(4).
Now,policymakershavetoconsiderwhattypesofenergysourceswillbeusedtopowerthesevehicles.
Theenergy-relateddecisionswillinevitablyinvolvecompromiseamongmultipleobjectives.
Asanalyzedinthiswork,itisthecurrenthighemissionsofpowerplantsthataregoingtomakeEVsalessfavorableoptionthanotheralternativesinChina,suchasHEVs,whicharemoreenvironmentallyfriendly,morecommerciallymature,andlesscost-intensive.
Currently,intheChinesevehiclemarket,takingproductsoftheBYDCompanyasanexample,HEVs(20,000-25,000U.
S.
dollars)aremuchmoreexpensivethanconventionalICEVs(8000-10,000U.
S.
dollars)ofequivalentsize,butthepriceofEVsisevenhigher(>30,000U.
S.
dollars).
Thecostsandbenetsofdifferenttechnologicaloptionsneedtobefurtherexplored.
InordertomakeEVsanattractiveoptionforChina,specialstrategiesforemissioncontrolofcoal-redpowerplantswillberequiredasthedevelopmentofEVsprogresses.
ThegovernmentshouldnominateappropriateplaceswithlowcarbonelectricityfortheintroductionofEVs.
Also,advancedcoalcombustiontechnologies,aswellastechnicalmeasurestoremovepollutants(suchasSCRandcoalcleaning),thoughcost-intensive,butnottechnicallydifcultanymore,shouldbeappliedwidelywiththenancialsupportofthegovern-ment,especiallyconsideringthefactthattherewouldbehugecobenetstohumanhealthandotherenvironmentissuesiftheperformanceofpowerplantswastobeimproved.
Itshouldbenotedthatbecausepowerplantshavealongerlifetimethanvehicles,thetechnologyshiftinthepowersectorcouldbeslowerthanthatofthetransportationsector.
Therefore,coordinatedpoliciesbetweenthesetwosectorsareneededtoreinforceEVs'progresstowardacleanerfuture.
ThegoodnewsisthatChinahasshownarmcommit-menttopromptrenewableenergyuse,improvingenergyefciencyandreducingpollutantemissionsfrompowerplants.
Greateffortshavebeen,andwillcontinuetobe,madebytheChinesegovernmenttoreducetheemissionsofpowerplants,suchassettinganaggressivetargettoreducenationalSO2emissionsby10%from2005to2010byinstallingFGDandclosingalargenumberofsmallgeneratingunits.
Moreactionsareunderdiscussioninthe"TwelfthFive-YearPlan(2011-2015)"toreduceNOxemissions.
AsthemassuseofEVswillplacefurtherpressuresonpowerplants,thereisanurgentneedtoacceleratethisprocess.
AnotherimportantissueworthmentioningisthatEVswouldprobablyimproveurbanairqualitybyreplacinggasolinevehicles,becausevehicleexhaustshavebecometheprimarycontributortoemissionsandambientconcentrationsofairpollutantsinmanyChinesecities(38).
Powerplants,especiallythenewones,areusuallylocatedfartherawayfromurbancentersthanvehicletailpipes.
Fromthepointofviewofhealthimpacts,urbanemissionsshouldbeoneoftheindicatorsoftheenvironmentalimpactsofEVs(39).
ThenextstepofourworkwillbetobetterunderstandtheimpactsofEVsonurbanairqualitybyintegratinglife-cycleemissioninventoriesofthevariousvehicletechnologiesintoanairqualitymodelingframeworkforChinesecities.
AcknowledgmentsThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(20625722and20921140409).
SupportingInformationAvailableDataonspecicationofcoalusedinChina,FGDpenetrationinChinesecoal-basedpowerplants,andadjustedparametersintheGREETmodelandotherkeyvariables.
ThismaterialisavailablefreeofchargeviatheInternetathttp://pubs.
acs.
org.
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