Abstract
Approximately 900 whole air samples were collected and assayed for selected C2‐C10hydrocarbons and seven halocarbons during the 5‐week Arctic Boundary Layer Expedition (ABLE) 3B conducted in eastern Canadian wetland areas. In more than half of the 46 vertical profiles flown, enhanced nonmethane hydrocarbon (NMHC) concentrations attributable to plumes from Canadian forest fires were observed. Urban plumes, also enhanced in many NMHCs, were separately identified by their high correlation with elevated levels of perchloroethene. Emission factors relative to ethane were determined for 21 hydrocarbons released from Canadian biomass burning. Using these data for ethane, ethyne, propane,n‐butane, and carbon monoxide enhancements from the literature, global emissions of these four NMHCs were estimated. Because of its very short atmospheric lifetime and its below detection limit background mixing ratio, 1,3‐butadiene is an excellent indicator of recent combustion. No statistically significant emissions of nitrous oxide, isoprene, or CFC 12 were observed in the biomass‐burning plumes encountered during ABLE 3B. The presence of the short‐lived biogenically emitted isoprene at altitudes as high as 3000 m implies that mixing within the planetary boundary layer (PBL) was rapid. Although background levels of the longer‐lived NMHCs in this Canadian region increase during the fire season, isoprene still dominated local hydroxyl radical photochemistry within the PBL except in the immediate vicinity of active fires. The average biomass‐burning emission ratios for hydrocarbons from an active fire sampled within minutes of combustion were, relative to ethane, ethene, 2.45; ethyne 0.57; propane, 0.25; propene, 0.73; propyne, 0.06;n‐butane, 0.09;i;‐butane, 0.01; 1‐butene, 0.14;cis‐2‐butene, 0.02;trans‐2‐butene, 0.03;i‐butylene, 0.07; 1,3‐butadiene, 0.12;n‐pentane, 0.05;i‐pentane, 0.03; 1‐pentene, 0.06;n‐hexane, 0.05; 1‐hexene, 0.07; benzene, 0.37; toluene, 0.16.
Highlights
Human activities are altering the trace gas content of the atmosphere on a global scale
Based on many vertical characterizationsof the background conditions encountered during this experiment, the general trend was for the concentrations of halocarbons and NM
The vertical profile of isoprene implies that mixing within the boundary layer was rapid to altitudes as high as 3000 m
Summary
Human activities are altering the trace gas content of the atmosphere on a global scale. 1988, 1992;Blake et al, 1992; Singh and Zimmerman, 1992] purpose of assayingthe collected samples as rapidly as and in biomass-burningevents [Crutzen et al, 1979; Green- possible In this manner, most of the available 300 air berg and Zimmerman, 1984;Greenberget al., 1985;Cofer et samplingcanisterswere filled approximately times during al., 1988, 1989;Hegg et al, 1990;Levine, 1991;Wofsyet al., the project. Retention times on the DB-624 column were affected less by becausethe plot and DB-1 columnshave such different varyingamountsof H20 and CO2, qualitativestandards separationcharacteristicsth, eelutionorderof thehydrocar- were added to the whole air standard in the same manner as bonsis quitedissimilarsothat any coelutionof gaseson one weretheNMHCs. Only oneseparationcolumnwasusedin columnwas mostlikely resolvedon the other.This twofold the halocarbonanalysis,but peak symmetrystronglysugdissimilar chromatographyprovided nearly unequivocal geststhat coelutiondid not affectthe mixingratiosof the peakidentificationfor theC2-C6 NMHCs. Responsefactors sevenreported halocarbons. The numbersnext to the traces are the measuredmixing ratios for the particular cases.The average altitudes (in meters) at which the sampleswere collected are given at the end of the chromatograms
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