Isotopic composition of H2 from wood burning: Dependency on combustion efficiency, moisture content, and δD of local precipitation

Abstract

Differences in isotopic composition between the various sources of H2 are large, but only a few measurements have been carried out to constrain them. Two conflicting values have been published for H2 from biomass burning. Both rely on the assumption that the isotopic composition of H2 should scale with the isotopic composition of the precipitation at the location where the biomass grew. Here we test this hypothesis using 18 wood samples collected from various locations around the globe. The sample locations cover a range of δD content of H2 in precipitation, from below −120‰ in Siberia and Canada to −15‰ in Zimbabwe. The results confirm the predicted dependence of the H2 isotopic composition on the precipitation in the sampling region. The water content itself is found to at most slightly affect the results. Furthermore, δD of H2 depends strongly on combustion efficiency. Thus, the isotopic composition of H2 from biomass burning shows a strong variability around the globe and between different stages of a fire. It is suggested that, rather than a global bulk number, global models that attempt to reproduce the spatial and temporal distribution of δD in H2 should incorporate explicitly the variability of δD(H2) from biomass burning on δD in precipitation.