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Biosphere-Atmosphere Interactions

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Biosphere-Atmosphere Interactions
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  Chapter2 Biosphere AtmosphereInteractions Leadauthors: MaryC.Scholes·PatriciaA.Matrai. Meinrat O.Andreae· Keith A.Smith·MartinR. Manning Co-authors: Paulo Artaxo . Leonard A.Barrie·TimothyS. Bates ·JamesH.Butler· Paolo C iccioli . Stanislaw A. CieslikRobert J.Delmas·FrankJ. Dentener . Robert A. Duce . David J. Erickson III.IanE. Galbally . Alex B. Guenther Ruprecht Jaenicke· Bernd Iahne. Anthony J. Kettle- Ronald P. Kiene· Jean-Pierre Lacaux . Peter S. Liss .G. Malin Pamela A. Matson ·ArvinR. Mosier ·Heinz -Ulrich Neue ·Hans W. Paerl.Ulrich F. Platt·PatriciaK.Quinn Wolfgang Seiler . Ray F. Weiss 2.1 Introduction Thecontemporaryatmospherewascreatedasaresultofbiologicalactivitysometwobillionyearsago.Tothisday,itsnaturalcompositionissupportedandmodified,mostlythroughbiologicalprocessesoftracegasproductionanddestruction,whilealsoinvolvingphysicalandchemicaldegradationprocesses.Thebiospherehasama jor influenceonpresentenvironmentalconditions,bothonaregionalandglobalscale.Oneofthebestdocumentedandmostimportantindicatorsofglobalchangeistheprogressiveincreaseofanumberoftracegasesintheatmosphere,amongthemcarbondioxide(C0 2), methane(CH 4), andnitrousoxide (N 2 0),allofwhichareofbiosphericorigin.Thereisconsiderableuncertainty,however,regardingtheprocessesthatdeterminetheconcentrationanddistributionoftracegasesandaerosolsintheatmosphereandthecausesandconsequencesofatmosphericchange(AndreaeandSchimel 1989). ToimproveourunderstandingIGACcreatedanenvironmentformulti-disciplinarycollaborationamongbiologists,chemists,andatmosphericscientists.Thiswasessentialtodevelopanalyticalmethods,tocharacteriseecosystems,toinvestigatephysiologicalcontrols,todevelopandvalidatemicrometeorologicaltheory,andtodesignanddevelopdiagnosticandpredictivemodels(MatsonandOjima 1990). Interactionsbetweenthebiosphereandtheatmosphereare part ofacomplex,interconnectedsystem.Theemissionanduptakeofatmosphericconstituentsbythebiotainfluencechemicalandphysicalclimatethroughinteractionswith atmospheric photochemistryand Earth'sradiationbudget.ComparativelysmallamountsofCH 4 andN 20 presentintheatmospheremakesubstantialcontributionstotheglobalgreenhouseeffect.Inaddition,emissionsofhydrocarbons and nitrogenoxidesfrombiomassburningintheTropicsresultinthephotochemical production oflarge amount sofozone(03) and acidityinthetropicalatmosphere.Inturn,climatechangeandatmosphericpollutionaltertheratesandsometimeseventhedirectionofchemicalexchangebetweenthebiosphereandatmospherethroughinfluencesatbothindividualorganismandecosystemlevels.Recentandexpectedfuturechangesinlanduseandlandmanagementpracticesprovidefurtherimpetusforcloselyexaminingclimate-gasfluxinteractions.Anthropogenicinfluences, e.g, tropicaldeforestationandthewidespreadimplementationofagriculturaltechnologies,haveandwillcontinuetomakesignificantalterationsinthesourcesandsinksforthevarioustracegases.Tenyearsago,atthebeginningof IGAC, researcherssoughttoestablishthesourceandsinkstrengthofgasesindifferentkindsofecosystems,indifferentareasoftheworld.Specificgoalsoftheprogramme,relatedtothebiosphereincluded:•tounderstandtheinteractionsbetweenatmosphericchemicalcompositionandbiological and climaticprocesses;•topredicttheimpactofnaturalandanthropogenicforcingsonthechemicalcompositionoftheatmosphere;and•toprovidethenecessaryknowledgeforthepropermaintenanceofthebiosphereandclimate.Earlierextrapolationsofgasfluxesoverspace and timewereoftenbasedonasingle,orverysmall,setofmeasurements, and researcherssoughtfor representative sitesatwhichtomakethosecrucialmeasurements.IGAC brought anewfocusto the variabilityamongecosystems and regionsoftheworld,inordertounderstandbetterthefactorscontrollingfluxes(Galbally 1989). Forexample,studiesofCH 4 fluxfromwetlandsandricepaddiesof N 2 0fluxfromnaturalandmanagedecosystems,andofdimethylsulphide(DMS)emissionsfromoceans,consciouslyspannedgradientsoftemperature,hydrologicalcharacteristics,soiltypes,marinesystems,managementregimes, and nitrogendeposition.Oneresultofthisstrategyhasbeentherecognitionthatthesamebasicprocesseswereresponsibleforgasfluxesacrossregions,latitudinalzones,andenvironments.Thischaptergivesageneraloverviewoftheprogressthathasbeenmadeinthefieldasawholewithinthelastdecade,withemphasisonresearchactivitiesstimulated,initiated, and/or endorsedbytheIGACcommunity. It isnotourintenttoprovidecurrent G. Brasseur et al. (eds.),  Atmospheric Chemistry in a Changing World  © Springer-Verlag Berlin Heidelberg 2002 megan@igacproject.org The complete book is available at: http://www.igacproject.org/sites/all/themes/bluemasters/images/2003_Brasseur_AtmosphericChemistryinaChangingWorld.pdf   : .O M.C.Scholes•P.A.Matrai. M.O.Andreae .K.A.Smith.M.R.Manning assessmentsofalltracegassourceandsinkstrengths.asthosebudgetshavebeencompiled and published(withconsiderablecontributionsby IGAC researchers)inrecentIntergovernmentalPanelonClimateChange(IPCC)documents.ExamplesofresearchnotconductedwithintheIGACframework but relevanttothetopicareCH 4 fromlandfills.ruminantlivestock.andtermites;informationonthesetopicscanbefoundinIPCC(1996,1999)·Exchangesofbiogenictracegasesbetweensurfacesandtheatmospheredependontheproductionandconsumptionofgasesbymicrobialandplantprocesses.onphysicaltransportthroughsoils.sediments. and water.andonfluxacrossthesurface-airboundaries.Thus,tounderstandandpredictfluxes.studiesofwholeecosystemsarerequired.Thegoalsofresearchoverthepastdecadehavebeentodevelopanunderstandingofthefactorsthatcontrolflux,organisethemeasurementssothattheyareusefulforregionalandglobalscalebudgets. and usetheknowledgetopredicthowfluxesarelikelytochangeinthefuture.TheIGACProjectfocussedonissuesofspecificinterestoveranumberofdifferentgeographicalregionsofEarth.Avarietyofprojectshavebeenconductedoverthelasttenyears,manyofwhichaddressedissuesrelatedtoexchangebetweenthebiosphereandtheatmosphere.Severalfieldcampaigns.usingacombinationof measurement and modellingtechniques.have been conductedverysuccessfullyunderthe IGAC umbrella,e.g.insouthernAfrica (SAFARI 1992and2000)andinvariousoceanicregions(ACE-I, ACE-2. andACE-Asia)(seeA.5).Whycertaintracegaseswerestudiedtogetherandwhyvariousscientificapproacheswereadoptedtostudythemisdescribedinthischapter.Researchfindingsspecificallyrelatedtotheexchangeoftracegasesandaerosolsbetweentheatmosphereandtheterrestrial and marinebiosphereswillbegiven.Intheterrestrialsection.specialattentionisgiventobiomassburningandwetdepositionintheTropics.becauseofthesignificantcontributionmadebyIGACtotheseprogrammes.Wealsoconsidersomeoftheanthropogenicactivitiesthatalterbiosphere-atmosphereexchangeanddiscusspotentialfeedbacksrelatedtoclimatechange.regionallevelairpollution, and deposition.Inthemarinesection,emphasisisonthebiogeochemistryofDMS.giventhatthegreatestadvancesweremadeonthistopic.Thechapterconcludesbysummarisingthemajoraccomplishmentsofthelastdecadeandhighlightingsomeoftheremainingresearchchallenges. 2.2KeyBiogenicGasesorFamiliesand their RelevancetoAtmosphericChemistry The study of atmospheric composition haslargelyfocussedontracecompounds that affecteithertheradiativepropertiesoftheatmosphere,orthebiosphereasnutrientsortoxins,or playa keyroleinatmosphericchemistry.Thetracegasesthatareimportantinthisregardhavebeensummarisedintheprecedingchapter.Thischapterconsiderstheroleofthebiosphereinemissionorremovalofsuchcompounds.AlthoughCO 2 andwater(H 2 0) arebothgreenhousegaseswhicharestronglyaffectedbythebiosphere.studiesofthesecompoundshavegenerallybeenconductedinparallelscientificcommunities, and IGAChasmaintainedafocusonthechemicallyreactivegreenhousegases.ThusnoattemptismadeheretocoverthelargebodyofresearchontheglobalcarboncycleandtheinteractionsofCO 2 withthebiosphere. 2.2.1TheCarbonFamily of Gases: CH4' VolatileOrganicCarbonCompounds (VOCs), andCarbonMonoxide (CO) Methane(CH 4) isagreenhousegaswithalifetimeintheatmosphereofaboutnineyears.Itsatmosphericconcentrationislargelycontrolledbythebiosphere,with70%ormoreofcurrentemissionsandvirtuallyallofpre-industrialemissionsbeingbiogenic(Fig. 2.1; Milich1999).ThedominantbiogenicproductionprocessforCH 4 ismicrobialbreakdownoforganiccompoundsin CIl ue: CIl -c: 0 セ セ セ ' we:. CIl 8E if セ 200100 0J---L-.l......:.- .:.......J: --:L.....L.. ..L....l .....L ........ ..L..J ...   --- --   _ セ -100 c c: -200 B c: -300 .Q -400 セ -500 -600 - n I- - Fig.2.1. Estimatedannualanthropogenicandnaturalsourcesandsinksofmethane (thickbars) inmillionsoftons,anduncertaintyranges (thinlines) (Milich1999) megan@igacproject.org  Fig. 2.2. Methanegrowthrates(figurecourtesyoftheNationalOceanic and AtmosphericAdministration(NOAA),ClimateMonitoring and DiagnosticsLaboratory(CMDLl.andCarbonCycle-GreenhouseGases(CCGG))0.5 CII  C   セ .; 0 CII C Vi -0.5 -1 CHAPTER 2. Biosphere -AtmosphereInteractions 21 CH 4 growthrate(nmol mor ' yr· l) 90·30· CII  C o· 3   ;  , ...J 30·90· 8485868788899091929394959697989900 Yearanaerobicconditions.Thisoccursinfloodedsoilssuchasnaturalwetlands and ricepaddies,inthe rumen ofanimalssuchascattle,inlandfills, and inanoxiclayersinthemarinewatercolumn and sediments.Methaneisalsoemitteddirectlytotheatmospherefrom burning vegetationasaproductofpyrolyticbreakdown of organicmaterial.Changesinlanduse,particularlyincreasesinnumbersofdomesticruminants,theextentofricepaddies, and biomassburning,havemore than doubledbiogenicCH 4 emissionssincethepre-industrialera(Milich1999;Ehhaltetal.2001).Fossilfuelrelatedemissions and adecreasein atmospheric oxidationrates (Thompson 1992)have further increasedCH 4 concentrations but thoseaspectsfalloutsidethescopeofthischapter.TheatmosphericconcentrationofCH 4 isnowabout1745 nmol mol' I, comparedtopre-industriallevels of about700nmol mol'. Growthrateshavebeenobserveddirectlyintheatmospheresincethe 1950S (Rinslandetal.198S;Zanderetal.1989) and onanincreasinglysys tematic basis since1978(Blake and Rowland1988;Dlugokenckyetal.1994).Concentrationswereincreasingatabout20nmol mol:' yr inthe1970sbutthatratehasgenerallydeclinedtoanaverageof5nmol mol yr· 1 overtheperiod1992to1998.Highgrowthratesofabout15nmolmol yr· 1 occurredin 1991 and 1998(Fig.2.2,Dlugokenckyetal.1998;Ehhaltetal.2001)andappeartobecausedbyclimaterelatedincreasesinwetlandand orbiomass burning emissions(Dlugokenckyetal.2000;Walter and Matthews2000).IPCC(2001)estimatesitsrateofincreaseat8.4nmol mol yr  . Theevolutionof the CH 4 budgetsincethepre-industrialeraprovidesagoodexampleofinteractionsbetweenlanduse and atmosphericchange.Aschematicofthechangeintotalemissionsfromthe18 th centurytothe present isshowninFig.2.3(basedonStern and Kaufmann1996,Lelieveldetal.1998,andHouwelingetal. Lifetime7.6yr8.4yrRemoval gg luxTgyr- 1 Atmospheric セ 1900Tg (4900Tg II burden (690 nmo l mol   )(1750nmolmOrl) Emission gg luxTgyr- 1 Pre-industrialCurrent Fig.2.3.Schematicofthepre-industrialHolocene andcurrent (1990S) atmosphericmethanebudget.Themeanlifetimederivedfromtheratioofatmosphericburdentoremovalratehasincreasedbyca. 10%, whichisbroadlyconsistentwithestimatesoftherelativedecreaseinOHfromatmosphericchemistrymodels(basedonSternandKaufmann (1996), Lelieveldetal. (1998) andHouwelingetal. (1999) (seealsoFig.7.4.) 1999).Theremovalratesthatarerequiredtobalancethesource-sinkbudgetatpre-industrial and presentconcentrationsimplyanincreaseinthemethanelifetime.Thisisconsistentwithindependentestimatesofadecreaseinatmosphericoxidationratesinferredfromchemistrymodels.Plantsemitarangeofvolatileorganiccarbon(VOCs) compounds, which include hydrocarbons ,alcohols,carbonyls,fattyacids, and esters,togetherwithorganicsulphurcompounds,halocarbons,nitricoxide(NO),CO, and organicparticles.Estimatesofanthropogenicemissionsfor1990areshowninFig.2.4.Accordingtocurrentestimatesplantsemitupto1200TgCyr- I asVOCs(Guentheretal.1995).Theamount of carbonreleasedfromthebiospherethiswaymaybeupto30%ofnetecosystemproductivity(NEP), i.e, theannualaccumulationofcarboninanecosystembeforetakingaccount megan@igacproject.org  22 M. C. Scholes· PA.Matrai.M.O. Andreae· K.A. Smith· M.R.Manning NMVOCfromanthropogenicsourcesin1990 Sources:lEA.UN,FAD,misc. o 60 30 -60 180 90 -30 セ 150 150 120120 90 90 6060 3030 oo -30-30 -60 -60 -90 -90 -120-120-150 -150 o I• 30 -180 90 -60 M Y P セ   ] ⦅ M]M]M ⦅ MMZMZ __ ;; '-_--:-: __ =--_--:-:-_----:-=--_--:-:-   Z Z ⦅ ] ]⦅セ -90-180180 -30 Globaltotal:171TgNVOC(min.=0.0.max.=1.2TG)Tangentcylinderprojection.Unit:GgNMVOClcell o 2 -10 _ 0-0 .110-50_0.1-1_50-1001 -2 _100-6200Calculation:G:NMV·sUM:Anthr.emissionsin1990Dataset(AL.EF):4:PUBLICDATAsET·VersionSource:EDGARlRIM+ Fig.2.4.Anthropogenicyearlynon-methaneVOCemissionsin1990fromtheEDGAR(EmissionDatabaseforGlobalAtmosphericResearch)database(Olivieret a1. 1996) ofecosystem disturbance (e.g.Valentinietal. 1997; Kesselmeieretal. 1998; Crutzenetal. 1999). NeglectofVOCandCOterrestrialemissionsmaycausesignificanterrorsinestimatesofNEPandchangesincarbonstorageforsomeecosystems.WhiletheoceansaresupersaturatedwithCOandsurfaceproductionofVOCsiswidespread,theoceanatmospherefluxesaresmall,butlesswellstudied,comparedwithterrestrialemissionestimates.VOCsshowawiderangeofreactivitiesinthetroposphere,withlifetimesrangingfromminutes(e.g. セ totwoweeks (e.g, methanol)(Atkinson and Arey 1998). Manyareemittedatverylowrates,andinsomecasesareoffsetbyplantuptake,thushavinganegligibleimpactonatmosphericchemistry;othersimpactozoneproduction(seeChap.3),aerosolproduction(seeChap.4),andtheglobalCObudget.Primarypollutantsemittedmainlyasaresultofhumanactivityincludehydrocarbons,CO,andnitrogenoxides.AbouthalftheterrestrialsurfaceemissionsofCOareduetodirectemissionsfromvegetation and biomassburning.Inadditionabout45%ofthetotalCOsourcetotheatmosphereisduetooxidationofmeth-ane and otherorganicsintheatmosphere,whichthemselvesarepredominantlybiogeniccompounds.BecauseCOistheendproductinthemethaneoxidationchainthetwobudgetsarecloselylinked;inaddition,COalsooriginatesfromthebreakdownofVOCs.TheconcentrationsofCOaretemporallyandspatiallyhighlyvariableduetotheshortlifetimeofCOandthenatureofitsdiscontinuouslandbasedsources.EstimatesofanthropogenicCOemissionsfor 1990 areshowninFig. 2.5. 2.2.2TheNitrogenFamily of Gases: Ammonia(NH 3), N 20, andNO Despiteitsimportanceforparticleformationandclimate,relativelylittleefforthas been spent onunderstandingthesourcesandremovalprocessesofNH 3• Mostworkonatmosphericammoniahasbeenperformedwithrespecttoeutrophicationandacidificationclosetotheterrestrialsources;largescaletransportandchemistryofNH 3 andammonium  NHt havereceivedmuchlessattention,especiallyoverremotemarineregions.Theglobalsourcestrengthofammoniaisabout megan@igacproject.org  CHAPTER 2.Biosphere-AtmosphereInteractions 23 COfromanthropogenicsourcesin1990«1kmAlt.) Sources:lEA.UN,FAO,misc. i ..., -18090 30 o -30 -60 -150-120-90 -60 -30 o 30 60901201501809060 30 o -30 セ -60 1502000 0 30 60 90120150   エ   -=- ..::J -90 -180180 Globaltotal:410TgCO-C (min. = 0.0.max. = 1.7TG)Tangentcylinderprojection.Source:EDGARlRIM+Calculation:G:CO-SUM:Anlhr.emissionsIn 1990 Dataset(AL):lEAEnergy 1992 Dataset(EF):GEIAfactorsandTNO-Inputdata 0 .02-0 .10 .1-0 .2.0.2-1.1-2 Unit: 10 9 kg CQ-C /cell o . 0-0 .002•0 .002-0 .010 .01-0 .02 Fi9.2.5.AnthropogenicannualCOemissionsin1990fromtheEDGARdatabase(OlivieretaJ.1996) 55TgNyr- I, whichisofsimilarmagnitudetoglobal NOx-N emission(Bouwmanetal.1997).ThemostrecentestimateforglobalNH 3 emissions(Bouwmanetal.1997)fromanimalsreliedonconstantemissionfactorsandamountedto 21.7 TgN yr , whichisofsimilarmagnitudeasfossilfuelrelatedglobal NOx-N emissions.Thesecondmost important emissioncategoryisN-containingsyntheticfertiliser.Again,hugedifferencesinagriculturalpracticeandenvironmentalconditionscausealargevariationofemissionsfactors.Overallglobalemissionofammoniaderivedfromnitrogenfertiliserwasestimatedtobe9Tgyr- I, whichis 10% ofthe amount applied.Interestingly, ammonia lossesfromapplicationofureafertilisertoricepaddiesseemtocontributestronglytothis.Otheranthropogenicsources,suchasbiomassburning,cropland,andhumansadditionallyemitabout10Tg yr' . Naturalsources,suchassoils,vegetation,andoceans,emitabout10-20Tg yr-I (Bouwmanetal.1997;SchlesingerandHartley iccz) andarehighlyuncertain.Nitrousoxideisanimportantgreenhousegaswithalifetimeofabout120years.ThelargestproductionprocessforN 2 0 is leakage duringmicrobialnitrificationanddentrificationprocessesinsoilandaquaticsystems.Significantemissionsalsooccurfromdecompositionofanimalwaste,oxidationofammonia(NH 3), andbiomassburning.BiogenicsourcesofN 2 0 haveincreasedwithexpansionoffoodproductionsystems,intensificationofagriculture,andanthropogenicmodificationoftheglobalnitrogencycle.Theconcentration ofN 2 0 hasincreasedfromabout270nmol mol inpre-industrialtimes(Kroezeetal.1999)to314nmolmol: today(CMDL2001).Thereissomeevidenceforsmallvariationsingrowthratesintheearly 1990S, butduringtheperiodofprecise insitu measurementsgrowthrateshaveremainednearconstantataround0.8nmol mol yr- I inbothhemispheres(CMDL2001).TheglobalN 2 0 fluxfromtheoceantotheatmospherehasbeencalculatedbasedonmore than 60000 fieldmeasurementsofthepartialpressureofN 2 0 insurfacewater(Fig.2.6).Thesedatawereextrapolatedgloballyandcoupledwithair-seagastransfercoefficientsestimatedonadailybasis(Nevisonetal.1995).Aglobaloceansourceofabout4(1.2-6.8)TgN yr' wasdeterminedandlatitudinalbandsofvaryingemissionweredelimited. megan@igacproject.org
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