Abstract
Elevated concentrations of hydrocarbons, CO, and nitrogen oxides were observed in extensive haze layers over northeastern Canada in the summer of 1990, during ABLE 3B. Halocarbon concentrations remained near background in most layers, indicating a source from biomass wildfires. Elevated concentrations of C2Cl4 provided a sensitive indicator for pollution from urban/industrial sources. Detailed analysis of regional budgets for CO and hydrocarbons indicates that biomass fires accounted for ≈ 70% of the input to the subarctic for most hydrocarbons and for acetone and more than 50% for CO. Regional sources for many species (including CO) exceeded chemical sinks during summer, and the boreal region provided a net source to midlatitudes. Interannual variations and long‐term trends in atmospheric composition are sensitive to climatic change; a shift to warmer, drier conditions could increase the areas burned and thus the sources of many trace gases.
Highlights
OBSERVATIONSIndustrial and urban emissionsprovide massiveinputs of Hydrocarbonasndhalocarbon(sincludingC2C14)[Blakeet al., pollutantsto borealand subarcticlatitudesin winterandspring; this issue] were determinedin grab samples,40 - 50 ratesfor depositionanddegradationare slow,andhigh pollutant electropolishceadnisterfsilledoneach5-hourflight,andanalyzed concentrationsare observed [Rahn, 1981; Bartie et al, 1985; in thelaboratoryusinggaschromatographSya. mpleacquisitionBattle, 1986; Stonehouse,1986; Bottenheim et al, 1986; Li and required30 - 60 s
This paper summarizes observed concentrations of intervalsand analyzedusingan on-boardgaschromatograph hydrocarbonsh,alocarbonsC,O, andnitrogenoxidesin theremote [Singhetal., thisissue]
We cantesthow well thesourcesthus defined accountfor observedbackgroundconcentrationbsy whereotiisthemeanvarianceratioforpollutanit fromTable1; examiningtheratioof termsontheright-handsidein equation(2)
Summary
Industrial and urban emissionsprovide massiveinputs of Hydrocarbonasndhalocarbon(sincludingC2C14)[Blakeet al., pollutantsto borealand subarcticlatitudesin winterandspring; this issue] were determinedin grab samples, - ratesfor depositionanddegradationare slow,andhigh pollutant electropolishceadnisterfsilledoneach5-hourflight,andanalyzed concentrationsare observed [Rahn, 1981; Bartie et al, 1985; in thelaboratoryusinggaschromatographSya. mpleacquisition. HydrocarboenmissionfsrombiomassfiresandratiostoCO and C2H2 are summarizedin Table 3a, determinedfrom hazelayers withunperturbehdalocarbocnoncentration(fslights4, 6-9, 11;see Figure for examples).Hazelayerssampledonflights18and (Table 3a, bottompanel) showedenhancementfsor long-lived speciessimilar to those in flights 4, 6-9, and 11, but no enhancemenot f shorter-livedhydrocarbons.These haze layers had apparentlyagedlong enoughfor short-livedspeciesto be removedby photochemistraynd for significantquantitiesof (CH3)2CO to begenerated. Emissionratiosfor mosthydrocarbonasre remarkablysimilar, the prevalenceof smolderingcombustiont;he associateldow relativeto CO or C2H2,frombiomasfsiresin a widerangeof NOx/hydrocarbroantiois responsibfloer thenegligiblreatesof environmentsin, cludingtundra,taiga, midlatitudesa,nd the ozonephotochemicparloductioonbservedin borealhazelayers tropics(seeTable3b). Nly a rough aredefineudnambiguoufsolryspeciewsithsmalsl patiavlariance;determinatioisnpossibldeueto the limitedgeographaicrea neitheris well definedfor gaseswith shortlifetimesand coveredandthebiasin selectinggrabsamplesF.igure shows concentratesdourcess, inceobservedconcentratiornesflectthetenthpercentlime easuremefonrtCO,C:H:, andC2H6 for particulacr ircumstanceosf dilution,advectiona,nd chemicaleachflightin thesubarctic.Flight 10 sampledgrosslypollutedair, reactionsoccurringafteremission.The presenat nalysisfocuses andflights14-16wereaffectedby anunusuailnfluxof tropicalair [Shiphamet al., this issue;Andersonet al., this issue;Harriss et ABLE-3B Fits 4 & 6/fire plumes al., thisissue,b].
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