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

Molecular hydrogen (H₂), its stable isotope signature (&delta;D), 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 &delta;D generally decrease with increasing fuel-to-air ratio, from ambient values of &sim;0.5 ppm and +130&permil; to 0.2 ppm and &minus;206&permil;, 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 &plusmn; 2.1 Tg, 6.3 &plusmn; 1.5 Tg, and 4.1 &plusmn; 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 &plusmn; 0.7 Tg, 2.8 &plusmn; 0.7 Tg, and 3.0 &plusmn; 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

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

“…Moreover, the resulting fossil fuel emission source magnitude of 3.2 TgH 2 /yr is outside the reported range of 5–25 TgH 2 /yr (see Table ) and is therefore considered unrealistic. Vollmer and Walter [] 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 TgH 2 /yr for the global emissions due to road transportation.…”

“…For the year 2005, they reported a value of 6.0±1.5 TgH 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 TgH 2 /yr and therefore equal to the emissions estimated by Vollmer and Walter []. However, the emissions as a result of residential burning processes used in this study (9.0 TgH 2 /yr) are much larger than the value of 2.8±0.7 TgH 2 /yr that was based on measurements performed in Switzerland.…”

“…However, the emissions as a result of residential burning processes used in this study (9.0 TgH 2 /yr) are much larger than the value of 2.8±0.7 TgH 2 /yr that was based on measurements performed in Switzerland. A possible explanation for the discrepancy between our results and those by Vollmer and Walter [] 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.…”

Emission of Hydrogen During Combustion of Plant Biomass Pellets on the Grate of a Low Power Boiler

“…Those papers, along with publications by Olsson and Kjällstrand (2002) and Kraszkiewicz (2016) include information that the use of solid bio-fuels in low-power heating devices makes problems with uncontrolled emission of many gaseous harmful products of incomplete combustion such as carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), volatile organic compounds (LZO) and tars. Works by Schultz et al (2003), Saxen et al (2008, Vollmer et al (2012) and Pieterse et al (2013) indicate the poorly recognized hydrogen (H2) emission, the presence of which in the atmosphere enhances the lifetime of greenhouse gases.…”

“…Kothari et al (2008) point out that the characteristic feature of hydrogen that can be determined its oxidation, thus emission into the atmosphere, is self-ignition temperature of 585 °C, which is even higher than that for methane 540 °C. Vollmer et al (2012) found that hydrogen presence launches other reactions, e.g. decomposition of NO to N2O.…”