Isotopic composition of H₂from wood burning: Dependency on combustion efficiency, moisture content, andδD of local precipitation

Abstract

[1] Differences in isotopic composition between the various sources of H 2 are large, but only a few measurements have been carried out to constrain them. Two conflicting values have been published for H 2 from biomass burning. Both rely on the assumption that the isotopic composition of H 2 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 dD content of H 2 in precipitation, from below −120‰ in Siberia and Canada to −15‰ in Zimbabwe. The results confirm the predicted dependence of the H 2 isotopic composition on the precipitation in the sampling region. The water content itself is found to at most slightly affect the results. Furthermore, dD of H 2 depends strongly on combustion efficiency. Thus, the isotopic composition of H 2 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 dD in H 2 should incorporate explicitly the variability of dD(H 2 ) from biomass burning on dD in precipitation.

The stable isotopic signature of biologically produced molecular hydrogen (H<sub>2</sub>)

“…As originally proposed by Gerst and Quay (2001) from budget closure, the photochemical sources of H 2 are also enriched in deuterium with δD between ∼ +100 ‰ and +200 ‰, (Rahn et al, 2003;Röckmann et al, 2003Röckmann et al, , 2010bFeilberg et al, 2007;Nilsson et al, 2007Nilsson et al, , 2010Pieterse et al, 2009 (Novelli et al, 1999;Hauglustaine and Ehhalt, 2002;Ehhalt and Rohrer, 2009;Pieterse et al, 2011) the extreme deuterium depletion relative to ambient atmospheric H 2 makes it a quite important contributor to the isotope budget (Price et al 2007;Pieterse et al 2011). An increasing demand and anthropogenic biological production of H 2 by e.g., industrial fermentation of biogenic waste material is associated with an expected release to the atmosphere because of leakage during production, storage, transport and use.…”

“…Tropospheric H 2 is enriched in deuterium with δD ∼ +130 ‰, (Gerst and Quay, 2001;Rhee et al, 2006;Rice et al, 2010;Batenburg et al, 2011) compared to surface emissions from fossil fuel combustion and biomass burning (δD approximately −200 ‰ and −300 ‰, respectively) (Gerst and Quay, 2001;Rahn et al, 2002;Röckmann et al, 2010a;Vollmer et al, 2010). As originally proposed by Gerst and Quay (2001) from budget closure, the photochemical sources of H 2 are also enriched in deuterium with δD between ∼ +100 ‰ and +200 ‰, (Rahn et al, 2003;Röckmann et al, 2003Röckmann et al, , 2010bFeilberg et al, 2007;Nilsson et al, 2007Nilsson et al, , 2010Pieterse et al, 2009 (Novelli et al, 1999;Hauglustaine and Ehhalt, 2002;Ehhalt and Rohrer, 2009;Pieterse et al, 2011) the extreme deuterium depletion relative to ambient atmospheric H 2 makes it a quite important contributor to the isotope budget (Price et al 2007;Pieterse et al 2011).…”

“…The measurements consist of the following steps: (1) The sample is cryogenically separated at −240 • C, which means that all gaseous compounds, with the exception of H 2 and some noble gases, are condensed; (2) The non-condensed fraction of the sample (including H 2 ) is preconcentrated using a 5Å molecular sieve at −210 • C; (3) H 2 is focused on a capillary gas chromatographic column (5Å molecular sieve) and chromatographically purified from remaining contaminants at 50 • C; (4) the D / H ratio of molecular H 2 is determined by continuous flow isotope ratio mass spectrometry using a ThermoFinnigan Delta Plus XL instrument. The analytical system is designed for measurement of air samples with H 2 mixing ratios in the range of typical atmospheric air samples (e.g., Röckmann et al 2003Röckmann et al , 2010bRhee et al 2006;Batenburg et al 2011). The samples obtained from the biogas reactor and the individual cultures have extremely high H 2 molar mixing ratios between 10 ppm and 1.4 % (see Table 1), which are outside the measurement range of our instrument.…”

“…The mixing ratio and isotopic composition of molecular H 2 was determined by using the experimental setup developed by Rhee et al (2004) and modified as described in Röckmann et al (2010b). Due to a lack of international isotope standards for H 2 , calibration is a critical issue.…”

The stable isotopic composition of molecular hydrogen in the tropopause region probed by the CARIBIC aircraft

“…The estimated magnitudes, isotopic signatures and uncertainties (superand subscript numbers) of the different surface sources were based on previous studies. For biomass burning, the estimated source signature was based on measurements that were later published in Röckmann et al (2010a). The magnitudes and isotope effects of the photochemical processes and the soil uptake were calculated from the model output; in this first H 2 study with TM5, no estimates of the uncertainties associated with these terms were made yet.…”