Abstract

Hydrochlorofluorocarbons (HCFCs) may be used as alternatives for the chlorofluorocarbons (CFCs). Lifetimes for the HCFCs are predicted here in two ways: integrating their loss with a global model, and scaling to another compound with a better known lifetime. Both approaches are shown here to yield similar results. Three‐dimensional fields of modeled tropospheric OH concentrations are used to calculate lifetimes against destruction by OH for the HCFCs and other hydrogenated halocarbons. The OH fields are taken from a three‐dimensional chemical transport model [Spivakovsky et al., 1990a] that accurately simulates the global measurements of methyl chloroform (derived lifetime of 5.5 yr). The lifetimes of various hydro‐halocarbons are shown to be insensitive to possible spatial variations and seasonal cycles. It is possible to scale the HCFC lifetimes to that of methyl chloroform or methane by using a ratio of the rate coefficients for reaction with OH at an appropriate temperature, about 277 K.

Highlights

  • Uncertainties in the calculated OH concentrations occur not Syntheticaplrloyducedhalocarbonsthatcontaincohnlolyriwneitahnthde kineticmodelb, ut alsowiththe global bromineo,ftencalledchlorofluorocar(bCoFnCssa) ndhalons,climatologoiefstheothetrracegaseasndcloudcovenr eeded posea directhreato thestratospheorziconelayer[e.g., asinputothephotochemmicoaldel.NASA/WMO1,986;Watsonetal., 1988]andalsocontribute TheOH fieldsusedhereweredevelopeadndappliedto substantiatlolythegreenhouesfefect[Ramanatha1n9,75; studymethycl hlorofor(mCH3CC1i3n)a three-dimensionalLacisetal.,1981].A singlceharacterisotfiCcFCsandhalonsChemicaTlransporMt odel(CTM)

  • One key propertyof longitudex altitudex time) is appliedhere to test various thesealternativecompoundms ustbe a shortatmospherichypotheseson the sensitivityof HCFC lifetimes to their residencteime,implyingefficientlossin thetropospheroer at tropospheridcistributioni;t is usedalsoto testthe accuracyof the earth's surface

  • The lifetime of yr4) toatmosphedreisctruct(iyorn-).Theglobalalyveragedm,ethyl chloroformderived from the ALE/GAGE analysisis annuaml eanlifetime(yr) of theHCFCs(againsat tmosphericoftenused[Prinn et al, 1987] andis thenscaledby the ratio loss)is definedastheglobalatmospherciconten(tkg)divided of therate coefficientsfor reactionwith OH [Hampsonet al., bythetotalannualloss(kgyr4)

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Summary

INTRODUCTION

Uncertainties in the calculated OH concentrations occur not Syntheticaplrloyducedhalocarbonsthatcontaincohnlolyriwneitahnthde kineticmodelb, ut alsowiththe global bromineo,ftencalledchlorofluorocar(bCoFnCssa) ndhalons,climatologoiefstheothetrracegaseasndcloudcovenr eeded posea directhreato thestratospheorziconelayer[e.g., asinputothephotochemmicoaldel. Hydrogen (hydrochlorofluorocarbonsor HCFCs), and The secondmethodfor derivingHCFC lifetimesselectsa atmosphericlossof theseHCFCs is dominatedby reaction reference specieswith a global budget and atmospheric with tropospheriOcH. Their abundancien the atmospherelifetime (againstOH destruction)that is thoughtto be well (units: kg) will be controlledby theratioof emission(skg understood [Makide and Rowland, 1981]. In thisreportwe derivethe lifetimeof HCFCs andother lifetime. [1983])andfromobserved of theintegrandvariesnonlinearlyoverthedomain,andthus climatologie(CsO,[03], CH4,NOx,H20 above500mbar,and thelossL will notbeequalto theproducotf theaveragesa, stratospheroiczonecolumn).Theobservationdaal tabasfeor pointmadebyMakideandRowland[,1981]. It ismisleading mostof thesespeciesis insufficiento definethe necessaryto reporta single"globalaverageOH concentratio(n)". The volume-averaOgeHddensitiys smalles6t,5 x 104cm-3, becausethe large volumesof low densityair in the upper tropospherehavelow OH concentrations

GLOBALOL SOSFCH3CCA1N3 DCH4
SENSITIVITY OF HCFC LIFETIME
Findings
Sensitivityto SeasonalCycles
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