Atmos. Chem. Phys. Discuss., 12, 6839-6875, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Molecular hydrogen (H2) combustion emissions and their isotope (D/H) signatures from domestic heaters, diesel vehicle engines, waste incinerator plants, and biomass burning
M. K. Vollmer1, S. Walter2, J. Mohn1, M. Steinbacher1, S. W. Bond1, T. Röckmann2, and S. Reimann1
1Empa, Swiss Federal Laboratories for Material Science and Technology, Laboratory for Air Pollution and Environmental Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
2Institute for Marine and Atmospheric research Utrecht, Utrecht University, Princetonplein 5, 3508TA Utrecht, The Netherlands

Abstract. Molecular hydrogen (H2), its stable isotope signature (δD), and the key combustion parameters carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4) were measured from various combustion processes. H2 in the exhaust of gas and oil-fired heaters and of waste incinerator plants was generally depleted compared to ambient intake air, while CO was significantly elevated. These findings contradict the often assumed co-occurring net H2 and CO emissions in combustion processes and suggest that previous H2 emissions from combustion may have been overestimated when scaled to CO emissions. For the heater exhausts, H2 and δD generally decrease with increasing fuel-to-air ratio, from ambient values of ∼0.5 ppm and +130‰ to 0.2 ppm and −206‰, respectively. These results are interpreted as a combination of an isotopically light H2 source from fossil fuel combustion and a D/H kinetic isotope fractionation of hydrogen in the advected ambient air during its partial removal during combustion. Diesel exhaust measurements from dynamometer test stand driving cycles show elevated H2 and CO emissions during cold-start and some acceleration phases. Their molar H2/CO ratios are <0.25, significantly smaller than those for gasoline combustion. Using H2/CO emission ratios, along with CO global emission inventories, we estimate global H2 emissions for 2000, 2005, and 2010. For road transportation (gasoline and diesel), we calculate 8.6 ± 2.1 Tg, 6.3 ± 1.5 Tg, and 4.1 ± 1.0 Tg, respectively, whereas the contribution from diesel vehicles has increased from 5% to 8% over this time. Other fossil fuel emissions are believed to be negligible but H2 emissions from coal combustion are unknown. For residential (domestic) emissions, which are likely dominated by biofuel combustion, emissions for the same years are estimated at 2.7 ± 0.7 Tg, 2.8 ± 0.7 Tg, and 3.0 ± 0.8 Tg, respectively. Our wood combustion measurements are combined with results from the literature to calculate biomass burning emissions. For these estimates, we propose a molar H2/CH4 ratio of 3.3, when using CH4 emission inventories. When using this approach, our resulting global biomass burning H2 emissions agree well with published results, suggesting that CH4 emissions may be a good proxy for H2 emissions.

Citation: Vollmer, M. K., Walter, S., Mohn, J., Steinbacher, M., Bond, S. W., Röckmann, T., and Reimann, S.: Molecular hydrogen (H2) combustion emissions and their isotope (D/H) signatures from domestic heaters, diesel vehicle engines, waste incinerator plants, and biomass burning, Atmos. Chem. Phys. Discuss., 12, 6839-6875, doi:10.5194/acpd-12-6839-2012, 2012.
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