The D/H content of methane emitted from biomass burning

The D/H content of methane emitted from biomass burning was measured using samples of smoke collected from large‐scale laboratory combustion experiments and from fires typical of slash burning of primary forest and of pasture burning in the Brazilian Amazon. In laboratory experiments, the mean δD of methane emitted fromPinus ponderosaneedle combustion (δDCH4(bb)) was −233 ± 2‰. In Brazilian fires, δDCH4(bb)was −210 ± 16‰. The measured D/H of the fuel biomass ranged from −59 to −125‰ and indicated a significant hydrogen isotope fractionation (ϵDBURN) during combustion. For the laboratory experiments, ϵDBURN(=(D/H)CH4/(D/H)Biomass‐l)1000 = −124‰ and in the field studies, ϵDBURNranged from −130 to −180‰. These results contrast those for δ13C which showed no fractionation during combustion, consistent with earlier studies. The measurements presented here suggest that a relatively narrow range exists for the δD of CH4emitted from biomass burning on a global scale and that δD is an independent tracer for atmospheric CH4. Combining δDCH4(bb)≈‐210‰ with literature values for the strength and δD of the major CH4sources, we estimate a δD for the global CH4source of ‐283 ± 13‰. This result provides a constraint for the D/H kinetic isotope effect associated with removal of atmospheric CH4by atmospheric hydroxyl radicals.