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EmissionFactorsandReal-TimeOpticalPropertiesofParticlesEmittedfromTraditionalWoodBurningCookstovesCHRISTOPHA.RODEN*ANDTAMIC.BONDDepartmentofCivilandEnvironmentalEngineering,UniversityofIllinoisatUrbana-Champaign,205NorthMathewsAvenue,Urbana,Illinois61801STUARTCONWAYTreesWater&People,633RemingtonStreet,FortCollins,Colorado80524ANIBALBENJAMINOSORTOPINELAHDESA,ColoniaCountryClub,CallePrincipalCasaNo2245,Comayaguela,MDCHondurasItisestimatedthatthecombustionofbiofuelgenerates20%ofallcarbonaceousaerosols,yettheseparticlesarestudiedlessthanthoseofothercommonsources.Wedesignedandbuiltaportablebattery-operatedemission-samplingcarttomeasurethereal-timeopticalpropertiesandotheremissioncharacteristicsofbiofuelcookstoves.InafieldstudyinHonduras,wemeasuredemissionfactorsaveraging8.5g/kg,higherthanthosefoundinpreviouslaboratorystudies.Strongflamingeventsemittedverydarkparticleswiththeopticalpropertiesofblackparticles.Theelementalcarbontototalcarbonratiosrangedfrom0.07to0.64,confirmingthathighelementalcarbonfractionscanbeemittedfrombiofuelcombustionandmaynotbeusedtodistinguishfossil-fuelfrombiofuelsourceswhencookingisthedominantusage.AbsorptionÅngstro¨mexponents,representingthedependenceofabsorptiononwavelength,rangedfrom1(black)to5(yellow).Stronglyabsorbingparticleswithabsorptioninverselydependentonwavelengthwereemittedseparatelyfromparticleswithweakabsorptionandstrongwavelengthdependence;thelatterprobablycontainedconjugatedaromaticcompounds.Becausecombustionoccursindistinctphases,differenttypesofcarbonaceousaerosolsfrombiofuelcombustionareexternallymixedatemissionandmayhavedifferentatmosphericfates.IntroductionMorethantwobillionpeopleusebiofuelssuchaswood,cropresidue,anddungastheirprimaryenergysourcefordomesticneedssuchasheatingandcooking(1).Biofuelisresponsibleforasignificantfractionofglobalblackcarbon(BC)andorganiccarbon(OC)aerosol.Itisestimatedtocontribute20%ofprimarypyrogenicBCandOCgloballyand33and65%,respectively,ofenergy-relatedpyrogenicBCandOC(2).Althoughthesevaluesaresimilartotheestimatedcontributionofdieselengines,37and16%ofenergy-relatedBCandOC,biofuelsourceshavebeenfarlessstudiedthanvehicularemissions.BCandOCareimportantcontributorstotheEarth’sradiativebalance;estimatesofclimateforcingrangefrom0.27to0.54and-0.04to-0.41W/m2,respectively(3),comparedwithaCO2forcingof1.45W/m2.Inadditiontoemittedquantities,thechemicalcompositionandopticalpropertiesofemissionsmustbeknownforclimatemodeling.Mostoftheparticlesfrombiofuelcombustionarecarbon-aceous(4),andthedifferencebetweenBCandOCisimportant.Blackcarbonabsorbsradiation,warmingtheatmosphereandcoolingtheground,whileorganiccarbonprimarilyscatterslight,coolingboththegroundandatmo-sphere.Someoftheinformationneededforclimateresearchisalsoofinterestforurbanandregionalairqualitystudies.Chemicalcompositionisneededforsourceapportionmentstudies,inwhichtheelementalcarbonfractionmaybeusedasatracerforvehicleexhaust(5).Particlemixing,orthecoexistenceoftwosubstancesinasingleparticle,mayaffecttherateofparticleremovalfromtheatmosphere;BCmayhavealongeratmosphericlifetimethanOC(6).Blackcarbonfromcombustionaffectspollutantpartitioning,particularlyforpolyaromatichydrocarbons(7).IfBCiscoatedbymaterialatemission,itssurfacemaynotbeavailabletoadsorbgaseousoraqueouspollutants.Severalstudieshavemeasuredbiofuelcombustionemis-sions(8-12).However,theseearlystudiesprovideinsuf-ficientinformationforseveralreasons.First,itisnotknownifthelaboratoryexperimentsaresimilartoevery-daycookingpractices.Whereaslaboratoryexperimentsstriveforuniformityandrepeatability,emissionsdependonfueltype,heatrequiredbydifferentfoodtypes,andthecook’sskillandattentionlevel.Fieldstudieshavere-portedgas-phasepollutants(13,14),butnotparticulatematter,exceptforonestudywhichmeasuredsimulatedcooking(15).Second,particulatechemicalcompositionhasonlyrecentlybeenreportedinonelaboratorystudy(16).Climate-relevantpropertiessuchasabsorptionandscat-teringhavebeenexaminedonlyforotherdissimilarsources,suchasopenbiomassburning(17).Finally,noneofthestudieshavereportedreal-timedata.Aswewillshow,suchinformationcanbevaluableininferringthenatureoftheparticles.Twolimitationsaccountfortheminimalfielddata.First,itcanbedifficulttoobtainaccesstorealsources,andsecond,biofuelisoftenusedinremotelocationswherelackofpowerrestrictsmeasurementcapabilities.Thepresentstudyover-comesbothofthesechallenges.Wedesignedandbuiltamobileemissionmeasurementplatform,theambulatoryreal-timeanalyzerforclimateandhealth-relatednoxiousemis-sions(ARACHNE),whichmeasuresemissionfactorsandreal-timeopticalpropertiesofemissionsinremotelocations.Along-standingcollaborationbetweentheUniversityofIllinois,TreesWaterandPeople(aU.S.-basednonprofitorganization),andtheHonduranAssociationforDevelopment(AHDESA),aHondurannonprofitorganization,allowedustoaccessemissionsfromrealcookingfires.Inadditiontotheirclimaticimpacts,biofuelemissionsalsohaveotherimportantadverseeffects.Highexposuresfromindoorcombustioncausehealthproblemssuchasacuterespiratoryillness.Thosemostaffectedarechildren,theelderly,and