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1058724 
Journal Article 
Molecular hydrogen (H sub(2)) emissions and their isotopic signatures (H/D) from a motor vehicle: implications on atmospheric H sub(2) 
Vollmer, MK; Walter, S; Bond, SW; Soltic, P; Roeckmann, T 
2010 
Yes 
Atmospheric Chemistry and Physics Discussions
ISSN: 1680-7367
EISSN: 1680-7375 
10 
2 
3021-3051 
English 
Molecular hydrogen (H sub(2)), its isotopic signature (deuterium/hydrogen, delta D), 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. H sub(2) 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, lambda ). The isotopic composition of H sub(2) ranged from delta D=-140ppt to delta D=-195ppt upstream of the TWC but these values decreased to -270ppt to -370ppt after passing through the TWC. Post-TWC delta D values for the fuel-rich range showed a strong dependence on TWC temperature with more negative delta D for lower temperatures. These effects are attributed to a rapid temperature-dependent H-D isotope equilibration between H sub(2) and water (H sub(2)O). In addition, post TWC delta D in H sub(2) showed a strong dependence on the fraction of removed H sub(2), suggesting isotopic enrichment during catalytic removal of H sub(2) with enrichment factors ( epsilon ) ranging from -39.8ppt to -15.5ppt depending on the operating mode. Our results imply that there may be considerable variability in real-world delta D emissions from vehicle exhaust, which may mainly depend on TWC technology and exhaust temperature regime. This variability is suggestive of a delta D from traffic that varies over time, by season, and by geographical location. An earlier-derived integrated pure (end-member) delta D from anthropogenic activities of -270ppt (Rahn et al., 2002) can be explained as a mixture of mainly vehicle emissions from cold starts and fully functional TWCs, but enhanced delta D values by >50ppt 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. 
Pollution Abstracts; Meteorological & Geoastrophysical Abstracts; Isotopes; Gasoline; Motor vehicles; Fuels; Deuterium; Temperature regime; Hydrogen; Emission control equipment; Carbon monoxide; upstream; hydrogen isotopes; Emissions; Seasonal variability; Exhaust emissions; Methane; Chemical composition; anthropogenic factors; Temperature; Atmospheric pollution by motor vehicles; traffic; Atmospheric chemistry; Technology; M2 551.510.42:Air Pollution (551.510.42); P 0000:AIR POLLUTION