Isotopic composition of H2 from wood burning: Dependency on combustion efficiency, moisture content, and δD of local precipitation
TL;DR: In this paper, the authors used 18 wood samples collected from various locations around the globe to investigate the dependence of the H2 isotopic composition on the precipitation in the sampling region.
Abstract: [1] 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.
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TL;DR: In this paper, measurements of CO2, CO, N2O and CH4 mole fractions, O2 / N2 ratios and the stable isotopes 13C and 18O in CO2 and CO have been performed in air samples from the Islisberg highway tunnel (Switzerland).
Abstract: . Measurements of CO2, CO, N2O and CH4 mole fractions, O2 / N2 ratios and the stable isotopes 13C and 18O in CO2 and CO have been performed in air samples from the Islisberg highway tunnel (Switzerland). The molar CO : CO2 ratios, with an average of (4.15 ± 0.34) ppb:ppm, are lower than reported in previous studies, pointing to a reduction in CO emissions from traffic. The 13C in CO2 reflects the isotopic composition of the fuel. 18O in CO2 is slightly depleted compared to the 18O in atmospheric O2, and shows significant variability. In contrast, the δ13C values of CO show that significant fractionation takes place during CO destruction in the catalytic converter. 13C in CO is enriched by 3‰ compared to the 13C in the fuel burnt, while the 18O content is similar to that of atmospheric O2. We compute a fractionation constant of (−2.7 ± 0.7)‰ for 13C during CO destruction. The N2O : CO2 average ratio of (1.8 ± 0.2) × 10−2 ppb:ppm is significantly lower than in past studies, showing a reduction in N2O emissions likely related to improvements in the catalytic converter technology. We also observed small CH4 emissions, with an average CH4 : CO2 ratio of (4.6 ± 0.2) × 10−2 ppb:ppm. The O2 : CO2 ratios of (−1.47 ± 0.01) ppm:ppm are very close to the expected, theoretically calculated values of O2 depletion per CO2 enhancement.
66 citations
TL;DR: It is shown that molecular hydrogen (H2) accumulates in silicate sand sediments due to decoupling of bacterial fermentation and respiration processes following anoxia, and that fermentation dominates anoxic carbon mineralization in these permeable sediments and is largely uncoupled from anaerobic respiration.
Abstract: Permeable (sandy) sediments cover half of the continental margin and are major regulators of oceanic carbon cycling. The microbial communities within these highly dynamic sediments frequently shift between oxic and anoxic states, and hence are less stratified than those in cohesive (muddy) sediments. A major question is, therefore, how these communities maintain metabolism during oxic–anoxic transitions. Here, we show that molecular hydrogen (H2) accumulates in silicate sand sediments due to decoupling of bacterial fermentation and respiration processes following anoxia. In situ measurements show that H2 is 250-fold supersaturated in the water column overlying these sediments and has an isotopic composition consistent with fermentative production. Genome-resolved shotgun metagenomic profiling suggests that the sands harbour diverse and specialized microbial communities with a high abundance of [NiFe]-hydrogenase genes. Hydrogenase profiles predict that H2 is primarily produced by facultatively fermentative bacteria, including the dominant gammaproteobacterial family Woeseiaceae, and can be consumed by aerobic respiratory bacteria. Flow-through reactor and slurry experiments consistently demonstrate that H2 is rapidly produced by fermentation following anoxia, immediately consumed by aerobic respiration following reaeration and consumed by sulfate reduction only during prolonged anoxia. Hydrogenotrophic sulfur, nitrate and nitrite reducers were also detected, although contrary to previous hypotheses there was limited capacity for microalgal fermentation. In combination, these experiments confirm that fermentation dominates anoxic carbon mineralization in these permeable sediments and, in contrast to the case in cohesive sediments, is largely uncoupled from anaerobic respiration. Frequent changes in oxygen availability in these sediments may have selected for metabolically flexible bacteria while excluding strict anaerobes. In sandy, permeable sediments, which frequently cycle between oxic and anoxic conditions, there is an uncoupling of fermentative and respiratory bacteria, and bacterial, rather than microalgal, fermentation drives the accumulation of hydrogen in this environment.
63 citations
01 Jan 2013
TL;DR: In this article, measurements of CO 2, CO, N 2 O and CH 4 mole fractions, O 2 /N 2 ratios and the sta-ble isotopes 13 C and 18 O in CO2 and CO have been performed in air samples from the highway tunnel Islisberg (Switzerland).
Abstract: Measurements of CO 2 , CO, N 2 O and CH 4 mole fractions, O 2 /N 2 ratios and the sta- ble isotopes 13 C and 18 O in CO2 and CO have been performed in air samples from the highway tunnel Islisberg (Switzerland). The CO:CO 2 ratios, with an average of (4.15±0.34)ppb:ppm, are lower than reported by previous studies, pointing to a re- 5 duction in CO emissions from tra c. The 13 C in CO2 reflects the isotopic composition of the fuel. 18 O in CO2 is slightly depleted compared to the 18 O in atmospheric O2, and shows significant variability. In contrast, the 13 C values of CO show that significant fractionation takes place during CO destruction in the catalytic converter. 13 C in CO is enriched by 3% compared to the 13 C in the fuel burnt, while the 18 O content is similar 10 to that of atmospheric O 2 . We compute a fractionation constant of ( 2.7±0.7)% for 13 C during CO destruction. The N
49 citations
TL;DR: In this paper, the isotope composition of molecular hydrogen (H 2 ) contains independent information for constraining the global H 2 budget, and a simplified but explicit isotope reaction scheme for the photochemical production of H 2.
Abstract: . The isotopic composition of molecular hydrogen (H 2 ) contains independent information for constraining the global H 2 budget. To explore this, we have implemented hydrogen sources and sinks, including their stable isotopic composition and isotope fractionation constants, into the global chemistry transport model TM5. For the first time, a global model now includes a simplified but explicit isotope reaction scheme for the photochemical production of H 2 . We present a comparison of modelled results for the H 2 mixing ratio and isotope composition with available measurements on seasonal to inter annual time scales for the years 2001–2007. The base model results agree well with observations for H 2 mixing ratios. For δD[H 2 ], modelled values are slightly lower than measurements. A detailed sensitivity study is performed to identify the most important parameters for modelling the isotopic composition of H 2 . The results show that on the global scale, the discrepancy between model and measurements can be closed by adjusting the default values of the isotope effects in deposition, photochemistry and the stratosphere-troposphere exchange within the known range of uncertainty. However, the available isotope data do not provide sufficient information to uniquely constrain the global isotope budget. Therefore, additional studies focussing on the isotopic composition near the tropopause and on the isotope effects in the photochemistry and deposition are recommended.
33 citations
TL;DR: In this article, molecular hydrogen (H2), its isotope signature (deuterium/hydrogen, δD), carbon monoxide (CO), and other compounds were studied in the exhaust of a passenger car engine fuelled with gasoline or methane and run under variable air-fuel ratios and operating modes.
Abstract: . Molecular hydrogen (H2), its isotopic signature (deuterium/hydrogen, δD), carbon monoxide (CO), and other compounds were studied in the exhaust of a passenger car engine fuelled with gasoline or methane and run under variable air-fuel ratios and operating modes. H2 and CO concentrations were largely reduced downstream of the three-way catalytic converter (TWC) compared to levels upstream, and showed a strong dependence on the air-fuel ratio (expressed as lambda, λ). The isotopic composition of H2 ranged from δD = −140‰ to δD = −195‰ upstream of the TWC but these values decreased to −270‰ to −370‰ after passing through the TWC. Post-TWC δD values for the fuel-rich range showed a strong dependence on TWC temperature with more negative δD for lower temperatures. These effects are attributed to a rapid temperature-dependent H-D isotope equilibration between H2 and water (H2O). In addition, post TWC δD in H2 showed a strong dependence on the fraction of removed H2, suggesting isotopic enrichment during catalytic removal of H2 with enrichment factors (e) ranging from −39.8‰ to −15.5‰ depending on the operating mode. Our results imply that there may be considerable variability in real-world δD emissions from vehicle exhaust, which may mainly depend on TWC technology and exhaust temperature regime. This variability is suggestive of a δD from traffic that varies over time, by season, and by geographical location. An earlier-derived integrated pure (end-member) δD from anthropogenic activities of −270‰ (Rahn et al., 2002) can be explained as a mixture of mainly vehicle emissions from cold starts and fully functional TWCs, but enhanced δD values by >50‰ are likely for regions where TWC technology is not fully implemented. Our results also suggest that a full hydrogen isotope analysis on fuel and exhaust gas may greatly aid at understanding process-level reactions in the exhaust gas, in particular in the TWC.
27 citations
References
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TL;DR: In this article, the authors present a set of emission factors for a large variety of species emitted from biomass fires, where data were not available, they have proposed estimates based on appropriate extrapolation techniques.
Abstract: A large body of information on emissions from the various types of biomass burning has been accumulated over the past decade, to a large extent as a result of International Geosphere-Biosphere Programme/International Global Atmospheric Chemistry research activities. Yet this information has not been readily accessible to the atmospheric chemistry community because it was scattered over a large number of publications and reported in numerous different units and reference systems. We have critically evaluated the presently available data and integrated these into a consistent format. On the basis of this analysis we present a set of emission factors for a large variety of species emitted from biomass fires. Where data were not available, we have proposed estimates based on appropriate extrapolation techniques. We have derived global estimates of pyrogenic emissions for important species emitted by the various types of biomass burning and compared our estimates with results from inverse modeling studies.
3,556 citations
"Isotopic composition of H2 from woo..." refers methods in this paper
...Higher values indicate inefficient combustion [Andreae and Merlet, 2001]....
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...The efficiency is quantitatively characterized by the ratio DCO/DCO2 = (COsample−COambient)/(CO2 sample−CO2 ambient) [Andreae and Merlet, 2001]....
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01 Oct 2015
TL;DR: This is the eighteenth in a series of evaluated sets of rate constants, photochemical cross sections, heterogeneous parameters, and thermochemical parameters compiled by the NASA Panel for Data Evaluation as mentioned in this paper.
Abstract: This is the eighteenth in a series of evaluated sets of rate constants, photochemical cross sections, heterogeneous parameters, and thermochemical parameters compiled by the NASA Panel for Data Evaluation. The data are used primarily to model stratospheric and upper tropospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. The evaluation is available in electronic form from the following Internet URL: http://jpldataeval.jpl.nasa.gov/
1,830 citations
TL;DR: In this paper, the accuracy of interpolated bD and δ 1 8 O estimates made using four methods is tested using resampling, and the best method lowers estimation error by 10-15% relative to others tested and gives an average error, using all available data, 2.5% of the global range.
Abstract: An accurate representation of the spatial distribution of stable hydrogen and oxygen isotopes in modern precipitation is required for many hydrological, paleoclimate, and ecological applications. No standardized method for achieving such a representation exists, and potential errors associated with previously employed methods are not understood. Using resampling, we test the accuracy of interpolated bD and δ 1 8 O estimates made using four methods. Prediction error for all methods is strongly related to number of data and will likely decline with the addition of new data. The best method lowers estimation error by 10-15% relative to others tested and gives an average error, using all available data, 2.5% of the global range. We present and interpret global maps of interpolated δD, δ 1 8 O, and deuterium excess in precipitation and the 95% confidence intervals for these values created using the optimal method. These depict global and regional patterns, make evident the robustness of interpolated isotopic patterns, and highlight target areas for future precipitation sampling.
1,071 citations
"Isotopic composition of H2 from woo..." refers methods in this paper
...org/), employing the IAEA database and interpolation algorithms developed by Bowen and Wilkinson [2002] and refined by Bowen and Revenaugh [2003] and Bowen et al....
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TL;DR: The precipitation maps show that the greatest potential for applying hydrogen and oxygen isotope forensics exists in mid- to high-latitude continental regions, where strong spatial isotope gradients exist and where strong, mechanistic relationships link precipitation and isotope ratios in biological tissue exist.
Abstract: Stable isotopes are being increasingly used in wildlife forensics as means of determining the origin and movement of animals. The heavy isotope content of precipitated water and snow (dDp, d 18 Op) varies widely and systematically across the globe, providing a label that is incorporated through diet into animal tissue. As a result, these isotopes are potentially ideal tracers of geo- graphic origin. The hydrogen and oxygen isotope tracer method has excellent potential where (1) spatial variation of precipitation isotopes exist, and (2) strong, mechanistic relationships link precipitation and isotope ratios in biological tissue. Here, we present a method for inter- polation of precipitation isotope values and use it to create global basemaps of growing-season (GS) and mean annual (MA) dDp and d 18 Op. The use of these maps for forensic application is demonstrated using previously published isotope data for bird feathers (dDf) in North America and Europe. The precipitation maps show that the greatest potential for applying hydrogen and oxygen isotope forensics exists in mid- to high-latitude conti- nental regions, where strong spatial isotope gradients exist. We demonstrate that dDf/dDp relationships have significant predictive power both in North America and Europe, and show how zones of confidence for the assignment of origin can be described using these predic- tive relationships. Our analysis focuses on wildlife forensics, but the maps and approaches presented here will be equally applicable to criminal forensic studies involving biological materials. These maps are available in GIS format at http://www.waterisotopes.org.
909 citations
"Isotopic composition of H2 from woo..." refers methods in this paper
...The Online Isotope Precipitation Calculator (OIPC; accessible at http://www.waterisotopes.org/), employing the IAEA database and interpolation algorithms developed by Bowen and Wilkinson [2002] and refined by Bowen and Revenaugh [2003] and Bowen et al. [2005] , was used to calculate annual dD values of meteoric water from wood sampling sites at the respective surface elevations....
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TL;DR: In this article, the authors empirically model relationships between oxygen isotope composition of modern precipitation and latitude and altitude, and then identify geographic areas where large-scale vapor transport patterns give rise to significant deviations from model δ18Oppt compositions based on latitude, altitude.
Abstract: Proxy data reflecting the oxygen isotope composition of meteoric precipitation (δ18Oppt) are widely used in reconstructions of continental paleoclimate and paleohydrology. However, actual geographic variation in modern water compositions is difficult to estimate from often sparse data. A first step toward understanding the geologic pattern of change in δ18Oppt is to describe the modern distribution in terms of principal geographic parameters. To this end, we empirically model relationships between 18O in modern precipitation and latitude and altitude. We then identify geographic areas where large-scale vapor transport patterns give rise to significant deviations from model δ18Oppt compositions based on latitude and altitude. Model value and residual grids are combined to derive a high-resolution global map of δ18Oppt that can serve as a spatial reference against which proxy data for paleoprecipitation can be compared. Reiteration of the procedure outlined here, for paleo-δ18Oppt data, may illuminate past changes in the climatic and physiographic parameters controlling the distribution of δ18O regimes.
756 citations