June32014June182014 pubsacsorgest ID: 356852
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ProgressonUnderstandingAtmosphericMercuryHamperedbyUncertainMeasurementsDanielA.JaSethLyman,HelenM.Amos,MaeS.Gustin,JiaoyanHuang,NoelleE.Selin,LeonardLevin,ArnoutterSchure,RobertP.Mason,RobertTalbot,AndrewRutter,BrandonFinley,LyattJaegleViralShah,CrystalMcClure,JesseAmbrose,LynneGratz,StevenLindberg,PeterWeiss-Penzias,Guey-RongSheu,DaraFeddersen,MilenaHorvat,AshuDastoor,AnthonyJ.Hynes,HuitingMao,JeroenE.Sonke,FranzSlemr,JennyA.Fisher,RalfEbinghaus,YanxuZhang,andGrantEdwardsSchoolofScience,Technology,EngineeringandMathematics,UniversityofWashington,Bothell,Washington98011,UnitedStatesDepartmentofAtmosphericSciences,UniversityofWashington,Seattle,Washington98195,UnitedStatesBinghamEntrepreneurshipandEnergyResearchCenter,UtahStateUniversity,Vernal,Utah84078,UnitedStatesDepartmentofEarthandPlanetaryScience,HarvardUniversity,Cambridge,Massachusetts02138,UnitedStatesDepartmentofNaturalResourcesandEnvironmentalSciences,UniversityofNevada,Reno,Nevada89557,UnitedStatesEngineeringSystemsDivisionandDepartmentofEarth,AtmosphericandPlanetarySciences,MassachusettsInstituteofTechnology,Cambridge,Massachusetts89557,UnitedStatesPaloAlto,California94304,UnitedStatesElectricPowerResearchInstitute,PaloAlto,California94304,UnitedStatesDepartmentofMarineSciences&Chemistry,UniversityofConnecticut,Groton,Connecticut06340,UnitedStatesInstituteforClimateandAtmosphericScience,UniversityofHouston,Houston,Texas77004,UnitedStatesDepartmentofChemistry,CarrollUniversity,Waukesha,Wisconsin53186,UnitedStatesGraeagle,California96103,UnitedStatesDepartmentofMicrobiologyandEnvironmentalToxicology,UniversityofCalifornia,SantaCruz,California95064,UnitedStatesDepartmentofAtmosphericSciences,NationalCentralUniversity,Jhongli,320,TaiwanDepartmentofChemistry,UniversityofNewHampshire,Durham,NewHampshire03824,UnitedStatesDepartmentofEnvironmentalSciences,JozefStefanInstitute,Ljubljana,SloveniaAirQualityResearchDivision,EnvironmentCanada,Dorval,QuebecM3H5T4,CanadaDivisionofMarineandAtmosphericChemistry,RosenstielSchoolofMarineandAtmosphericScience,UniversityofMiami,Miami,Florida33149,UnitedStatesDepartmentofChemistry,StateUniversityofNewYork,CollegeofEnvironmentalScienceandForestry,Syracuse,NewYork13210,UnitedStatesObservatoireMidi-Pyrees,UniversitePaulSabatier,31062,Toulouse,FranceAtmosphericChemistryDivision,MaxPlanckInstituteforChemistry,Mainz,GermanyCentreforAtmosphericChemistry,UniversityofWollongong,Wollongong,NewSouthWales2522,AustraliaDepartmentofEnvironmentalChemistry,InstituteofCoastalResearch,Geesthacht,GermanySchoolofEngineeringandAppliedSciences,HarvardUniversity,Cambridge,Massachusetts02138,UnitedStatesFacultyofScience,MacquarieUniversity,Sydney,NewSouthWales2109,Australia June3,2014June18,2014 pubs.acs.org/est ©2014AmericanChemicalSocietyEnviron.Sci.Technol.2014,48,7204 ercury(Hg)isapotentneurotoxinandgloballyreducingenvironmentallevelsisseenasparamountforprotectinghumanandwildlifehealth.In2013,manycountriesnalizedthenegotiationson,andhavenowsigned,theMinamataConventiononMercury,whichcommitsparticipatingcountriestoreduceemissionsanduseofmercury.Successfulimplementationofthetreatywillrequireadequatevericationthroughglobalmonitoring.Inthepastdecade,thenumberofatmosphericmeasurementsofspeciatedHghasrapidlymultiplied.MercurydataarebeingcollectedbymonitoringnetworksinEurope,Canada,EastAsia,andtheUnitedStates.Thesemeasurementsarerelativelyexpensiveandmountingevidencesuggeststheysuerfromcantbiases.Asacommunity,weareconfrontedwiththeArecurrentanalyticalmethodsforHgadequatetoaddresspolicyrequirements?Weconcludethatbetteranalyticaltechniquesareurgentlyneeded.IntheatmosphereHgoccursasthreeoperationallydeforms:gaseouselementalmercury(GEM),gaseousoxidizedmercury(GOM)andparticle-boundmercury(PBM).GOMandPBMarebelievedtoconsistofHg(II)compounds.OxidationofGEMtoGOMandsubsequentdepositionisthoughttobethemajorpathwaytodeliverHgtoecosystems.Thus,GOMprovidesacriticallinkbetweenhumanemissionsandecosystemexposure.Anumberoflaboratoryandtheoreticalchemicalinvestigationshavebeenperformed,butatpresentthereisnoconsensusonwhatthechemicalform(s)ofGOMis(are),noranyreliablemethodtoidentifythechemicalform(s)intheatmosphere.ItislikelythatmorethanoneformofHg(II)existsintheatmosphere,dependingonitssource.AtpresenttheprimarymethodtoidentifyGOMisuseofaKClcoateddenuderforconcentrationandcollection,followedbythermaldesorptionandatomicuorescencetoquantifythedesorbedGEM.PBMiscollectedonaregenerablequartzlterdownstreamofthedenuderandisquantiedsimilarly.ThismethodhasbeenadoptedbytheCanadianAtmosphericMercuryNetwork,theU.S.AtmosphericMercuryNetworkandtheEuropeanGlobalMercuryObservationSystemforstandardmeasurements.QA/QCprotocolshavebeendevelopedforthesenetworks,buttheseprotocolsdonotprovideawaytocalibrateforGOMorPBM,quantifycollectioneciencyorquantifymeasurementinterferences.AnumberofstudieshavebeenpublishedthatindicatetherearesignicantproblemswiththeexistingmethodsforGOMandPBM.ByusingpossibleGOMcompounds,suchasHgClandHgBr,ithasbeenshownthattheKCldenudermethodissubjecttointerferencesfromozone,watervaporandpossiblyothercompoundsaswell.1,2OtherstudieshavefoundthatKCldenudermeasurementsdonotagreewithmeasurementsmadewithalternativecollectionsurfaces.ItisalsonotclearwhatisthetrueuncertaintyinmeasurementsofPBM,ascom-parisonswithothermethodshaveyieldedlargediscrepanciesbetweencommercial,automatedPBMmeasurementsandmanualmethodswithalternativesamplers.AllofthesepointtosubstantialproblemswithourcurrentmethodstoquantifyGOMandPBM.AtpresentwearenotabletoquantifytheuncertaintyinGOMandPBMmeasurements.Thisisbecause(1)wedonotknowthechemicalformbeingmeasured,(2)thereisnoacceptedcalibrationmethodand(3)wehavealimitedunderstandingofinterferences.ItisnotyetclearwhetherwewillbeabletocorrectGOMandPBMdatacollectedwithcurrentmethodstoaccountforthesebiases.ThiswillrequireamoredetailedunderstandingofHgchemistryanddetailedinterferencetestswithreliableeld-deployablecalibrators.WeacknowledgethatsomemeasurementsofGOMmadewiththeKCldenudermethodhavebeensuccessfullyinterpreted,atleastqualitatively.SomestudieshavedemonstratedaninverserelationshipandapproximatemassconservationbetweenGOMandGEM.However,thesestudiesdonotprovidedenitiveevidencethattheKCldenudermethodisfreefrombias.WorkinvestigatingozoneinterferencehasfoundthattheratioofGOMtoGEMcanbebiasedlowwhilethetotalgaseousHgconcentration(GOM+GEM)isapproximatelyconserved.Inotherwords,GOMcandecomposetoGEMduringsamplingandbeanalyzedasGEM.ItisalsopossiblethattheKCldenudermethodworksbetterinsomeenvironmentsthanothers.Atpresent,webelieveunspeciatedHgmeasurements(i.e.,measurementswithnoupstreamprocessingpriortosampleintroductionintoanatomicuorescenceanalyzer)arewellcalibratedandthetrueuncertaintycanbereasonablydescribed.Thereissomeuncertaintyastowhethercurrentunspeciatedmeasurementscapturetotalgaseousmercury(TGM)orGEM.Ifdesired,totalatmosphericmercury(TAM=GEM+GOM+PBM)canbemeasuredusingapyrolyzinginlet.Inprinciple,measurementsofTAMshouldbemoreaccuratethancurrentmethodstomeasuretheindividualspecies.WorkingwithHg(II)compoundsischallengingduetotheirtoxicity,tendencytodecompose,andstickinessincalibrationsystems.Butwithouthighqualitycalibrationsitisnotpossibletovalidatemeasurements,quantifyuncertaintiesorfullyevaluateatmosphericmodels.CalibrationmethodsforoxidizedHgcom-poundsareimprovingandthesewillimprovethequalityoffutureinterferencestudiesaswellasroutinemeasurementstudiesforGOMandPBM.Inordertohavecondenceinatmosphericchemicalmeasure-ments,wemustbeabletoquantifytheiruncertainty.Thisincludesroutinecalibrationinrealisticconditionsandrigoroustestingforinterferences.Atpresent,theexistingandplannedatmosphericmercurynetworkshaveinadequateattentiontoqualitycontrolforGOMandPBMmeasurements.Toresolvetheseissues,thecommunityneedsto1DevelopcalibrationmethodsforGOMandprovideroutinecalibrationsforeldinstrumentation; EnvironmentalScience&Technology Environ.Sci.Technol.2014,48,7204 2ConductdetailedinvestigationstoquantifyinterferencesintheexistingGOMmethodsanddevelopnewmethod-ologiestomeasureit;and3Conductfundamentalresearchonthechemistry,reactionkineticsandchemicalidentityofthecompoundsthatmakeupGOMandPBMintheatmosphere.Webelievetheseitemsshouldbegivenhighprioritybythemercuryscienticcommunity.Todootherwiseimpedesscientiprogressandenvironmentalmonitoringeorts.Spacelimitationspreventusfromincludingacompletesetofrelevantreferences.Foramorecompletelistofrelevantpublications,pleasegotohttp://atmos.washington.edu/jaegroup/modules/hg/AUTHORINFORMATIONCorrespondingAuthorE-mail:djaTheauthorsdeclarenocompetingnancialinterest.(1)Lyman,S.N.;Jaffe,D.A.;Gustin,M.S.ReleaseofmercuryhalidesfromKCldenudersinthepresenceofozone.Atmos.Chem.Phys.,81978204,DOI:10.5194/acp-10-8197-2010.(2)Gustin,M.S.;Huang,J.;Miller,M.B.;Peterson,C.;Jaffe,D.A.;Ambrose,J.;Finley,B.D.;Lyman,S.N.;Call,K.;Talbot,R.;Feddersen,D.;Mao,H.;Lindberg,S.E.Doweunderstandwhatthemercuryspeciationinstrumentsareactuallymeasuring?ResultsofRAMIX.Environ.Sci.Technol.(13),72957306,DOI:10.1021/(3)Talbot,R.;Mao,H.;Feddersen,D.;Smith,M.;Kim,S.Y.;Sive,B.;Haase,K.;Ambrose,J.;Zhou,Y.;Russo,R.Comparisonofparticulatemercurymeasuredwithmanualandautomatedmethods.20,DOI:10.3390/atmos2010001.(4)Kos,G.;Ryzhkov,A.;Dastoor,A.;Narayan,J.;Steffen,A.;Ariya,P.A.;Zhang,L.Evaluationofdiscrepancybetweenmeasuredandmodelledoxidizedmercuryspecies.Atmos.Chem.Phys.4863,DOI:10.5194/acp-13-4839-2013.(5)Finley,B.D.;Jaffe,D.A.;Call,K.;Lyman,S.;Gustin,M.;Peterson,C.;Miller,M.;Lyman,T.Development,testing,anddeploymentofanairsamplingmanifoldforspikingelementalandoxidizedmercuryduringtheRenoAtmosphericMercuryIntercomparisonExperimentEnviron.Sci.Technol.,DOI:10.1021/es304185a. EnvironmentalScience&Technology Environ.Sci.Technol.2014,48,7204