Some trace gas emissions from North American biomass fires with an assessment of regional and global fluxes from biomass burning

Authors

  • Krista K. Laursen,

  • Peter V. Hobbs,

  • Lawrence F. Radke,

  • Rei A. Rasmussen


Abstract

Emission factors for several trace gases were determined using airborne measurements from 13 biomass fires in North America. Emissions of methane (CH4), nonmethane hydrocarbons (NMHC), hydrogen (H2) and ammonia (NH3) were found to be positively correlated with the ratio of carbon monoxide (CO) to carbon dioxide (CO2) emission factors, both within each fire and between fires. This indicates that these four species are produced predominantly when combustion is inefficient. Methyl chloride (CH3Cl) emission factors were positively correlated with the ratio of CO to CO2 emission factors within the majority of the fires. However, a linear regression of the average CH3Cl emission factor for each fire onto the average ratio of the CO to CO2 emission factors produced a negative correlation coefficient. This indicates that the variance in CH3Cl emissions between fires is not due to differences in overall combustion efficiency. (According to previous research, differences in fuel chlorine content are mainly responsible for the differences in emissions of CH3Cl between fires.) The average NOx emission factors for three biomass fires in southern California were found to be significantly higher than the average NOx emission factors for the remaining 10 fires studied. It is suggested that this difference is due to an enhanced nitrogen content (possibly the result of pollutant deposition and in some cases nitrogen fixation) of the fuels consumed, and the consumption of large amounts of foliage during the three fires. The average NOx/CO2 molar ratio determined from this study (2.1 × 10−3) is consistent with results from other airborne and laboratory studies of biomass burning emissions. However, the N2O/CO2 molar ratios resulting from this study are roughly a factor of 2 larger than N2O/CO2 molar ratios obtained from laboratory studies. It is hypothesized that the higher N2O/CO2 molar ratios presented here are primarily due to emissions of N2O from the soil Overall average emission factors derived from this study were used to estimate the fluxes of several trace gases from temperate and boreal biomass fires. In addition, a new method is outlined for estimating fluxes of CH4, NMHC, H2 and NH3 from global biomass burning. The annual emissions of these four species from worldwide biomass burning are determined by this method to be 39, 17, 21 and 4.5 Tg yr−1, respectively. Our results indicate that the worldwide emissions of CH4, NMHC, H2 and NH3 from biomass burning represent 8%, 17%, 24% and 7%, respectively, of the total global emissions of these four species.

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