Volatile organic trace gases emitted from North American wildfires

Trace gases from wildfires and prescribed burns were collected from the Nat ional Science Foundation (NSF)/National Center for Atmospheric Research (NC AR) C-130 aircraft at fire locations in temperate forests (Montana, Colorad o) and sage scrub (California). Comprehensive compositions for hydrocarbons , partially oxidized hydrocarbons (POHC), halocarbons, alkyl nitrates, and some sulfur compounds were determined in 99 samples. All of these trace gas emission groups correlated linearly with CO emissions. Fires in temperate forests emitted similar to 28% more nonmethane hydrocarbons (NMHC) and 120% more POHC than the California fire and the molecular weight range of the e mitted hydrocarbons was higher. The POHC contribution relative to NMHC emis sions is significant: 26 and 38% for California and temperate forests, resp ectively. Since the observed POHCs (mostly ketones, aldehydes, and furans) typically react faster than many NMHC and undergo cascades of photochemical degradations, they should be included in calculations of the effect that f ires have on the local and global oxidative capacity of the atmosphere. The composition of the hydrocarbons and POHCs in the plumes varied with combus tion efficiency, displaying a distinct pattern, which reflected fire chemis try. Interfire differences were evident among fires in temperate forests. T he dominant halocarbon emissions from all fires were methyl halides. The em ission ratio was always largest for methyl chloride and was dependent on ve getation and fire location. C-1-C-5 alkyl nitrates were found in all fire e missions and showed little dependence on the location of the fire. The majo r organic sulfur compound measured was carbonyl sulfide. Minor amounts of d imethyl sulfide and dimethyl disulfide were observed. Budget estimates for emissions from fires in temperate forests were made based on the measured e mission ratios and published carbon monoxide estimates.