Molecular hydrogen (H<sub>2</sub>) combustion emissions and their isotope (D/H) signatures from domestic heaters, diesel vehicle engines, waste incinerator plants, and biomass burning

Abstract

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 gas and oil-fired heater exhausts, H2 and δD generally decrease with increasing CO2, 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. While H2 and CO emissions from diesel vehicles are known to be significantly less than those from gasoline vehicles (on a fuel-energy base), we find that their molar H2/CO ratios (median 0.026, interpercentile range 0.12) are also significantly less compared to gasoline vehicle exhaust. 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 8.3 ± 2.2 Tg, 6.0 ± 1.5 Tg, and 3.8 ± 0.94 Tg, respectively, whereas the contribution from diesel vehicles is low (0.9–1.4%). 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. For biomass burning H2 emissions, we derive a mole fraction ratio ΔH2/ΔCH4 (background mole fractions subtracted) of 3.6 using wildfire emission data from the literature and support these findings with our wood combustion results. When combining this ratio with CH4 emission inventories, the resulting global biomass burning H2 emissions agree well with published global H2 emissions, suggesting that CH4 emissions may be a good proxy for biomass burning H2 emissions.

Reassessing the variability in atmospheric H2 using the two‐way nested TM5 model

“…in Switzerland. A possible explanation for the discrepancy between our results and those by Vollmer et al [2012] may be that the latter are not representative for the entire domain of the EuroHydros observations and that H 2 emissions from natural gas may be significantly larger.…”

“…For the year 2005, they reported a value of 6.0˙1.5 Tg H 2 /yr for the global emissions due to road transportation. Although the aggregated overall fossil fuel emissions in our study are much larger, the part assigned to road transportation is 6.9 Tg H 2 /yr and therefore equal to the emissions estimated by Vollmer et al [2012]. However, the emissions as a result of residential burning processes used in this study (9.0 Tg H 2 /yr) are much larger than the value of 2.80 .7 Tg H 2 /yr that was based on measurements performed The stratospheric correction is part of the overall value for the isotopic composition relative to VSMOW down to 100 hPa.…”

“…Moreover, the resulting fossil fuel emission source magnitude of 3.2 Tg H 2 /yr is outside the reported range of 5-25 Tg H 2 /yr (see Table 3) and is therefore considered unrealistic. Vollmer et al [2012] recently suggested a strong decrease in H 2 fossil fuel related emissions between 2000 and 2010. For the year 2005, they reported a value of 6.0˙1.5 Tg H 2 /yr for the global emissions due to road transportation.…”

Biomass burning emissions of trace gases and particles in marine air at Cape Grim, Tasmania

“…The ER of BC to CO reported here is in good agreement with BC to CO ERs in smouldering fires (MCE < 0.9) reported by Kondo et al (2011) and May et al (2014), which suggests that the excess CO 2 and MCE has been determined reliably. Whole of fire emission factors were calculated according to the carbon mass balance method (Ward and Radke, 1993). Emission factors were calculated relative to combusted fuel mass (Andreae and Merlet, 2001), assuming 50 % fuel carbon content by dry weight according to the following equation:…”

Isotopic signatures of production and uptake of H&lt;sub&gt;2&lt;/sub&gt; by soil

“…The δD of H 2 from various surface sources has been reported as about −290 ‰ for biomass burning (Gerst and Quay, 2001;Haumann et al, 2013) and between −360 and −200 ‰ for fossil fuels combustion (Rahn et al, 2002b;Vollmer et al, 2012). So far no field studies have determined the isotopic composition of H 2 emitted from soil.…”