Volatile organic trace gases emitted from North American wildfires

Abstract

Trace gases from wildfires and prescribed burns were collected from the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) C-130 aircraft at fire locations in temperate forests (Montana, Colorado) 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 emission. Fires in temperate forests emitted ∼ 28% more nonmethane hydrocarbons (NMHC) and 120% more POHC than the California fire and the molecular weight range of the emitted hydrocarbons was higher. The POHC contribution relative to NMHC emissions is significant: 26 and 38% for California and temperate forests, respectively. 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 fires have on the local and global oxidative capacity of the atmosphere. The composition of the hydrocarbons and POHCs in the plumes varied with combustion efficiency, displaying a distinct pattern, which reflected fire chemistry. Interfire differences were evident among fires in temperate forests. The dominant halocarbon emissions from all fires were methyl halides. The emission ratio was always largest for methyl chloride and was dependent on vegetation and fire location. C1-C5 alklyl nitrates were found in all fire emissions and showed little dependence on the location of the fire. The major organic sulfur compound measured was carbonyl sulfide. Minor amounts of dimethyl sulfide and dimethyl disulfide were observed. Budget estimates for emissions from fires in temperate forests were made based on the measured emissions ratios and published carbon monoxide estimates.