Hydrogen and carbon isotopic measurements of methane from agricultural combustion: Implications for isotopic signatures of global biomass burning sources

Abstract

The hydrogen and carbon isotope ratios of CH 4 emitted from one bonfire and two laboratory combustions of agricultural residues were determined in this study as -196 to -262‰ for δD and -19.9 to -35.1‰ for δ 13 C. The isotopic difference between CH 4 emitted from biomass burning and fuel biomass, that is, the apparent isotopic fractionation occurring during combustion (ε Burn), was within -101 to -174‰ for ε Burn D and +6.9 to -8.6‰ for ε Burn 13C. That difference varied according to burning conditions: flaming and smoldering. Variation in ε Burn is correlated with combustion efficiency (CE), defined here as the ratio of emitted CO 2 to the sum of emitted CO 2 and CO. In light of the previously reported global distributions of CE, the implied ε Burn values for global biomass burning sources were -121‰ for ε Burn D and +2.29‰ for ε Burn 13C. Using the relationship between ε Burn and CE and global distributions of CE and isotopic ratios of fuel biomass, we estimated the global isotopic signature for biomass burning sources as -169‰ for δD and -23.6‰ for δ 13 C. Copyright 2006 by the American Geophysical Union.