Molecular hydrogen (H2) emissions and their isotopic signatures (H/D) from a motor vehicle: implications on atmospheric H2
Item
Title (Dublin Core)
Molecular hydrogen (H2) emissions and their isotopic signatures (H/D) from a motor vehicle: implications on atmospheric H2
Description (Dublin Core)
Molecular hydrogen (H<sub>2</sub>), its isotopic signature (deuterium/hydrogen, δ<i>D</i>), 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</sub> 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 H<sub>2</sub> ranged from δ<i>D</i> = −140‰ to δ<i>D</i> = −195‰ upstream of the TWC but these values decreased to −270‰ to −370‰ after passing through the TWC. Post-TWC δ<i>D</i> values for the fuel-rich range showed a strong dependence on TWC temperature with more negative δ<i>D</i> for lower temperatures. These effects are attributed to a rapid temperature-dependent H-D isotope equilibration between H<sub>2</sub> and water (H<sub>2</sub>O). In addition, post TWC δ<i>D</i> in H<sub>2</sub> showed a strong dependence on the fraction of removed H<sub>2</sub>, suggesting isotopic enrichment during catalytic removal of H<sub>2</sub> with enrichment factors (ε) ranging from −39.8‰ to −15.5‰ depending on the operating mode. Our results imply that there may be considerable variability in real-world δ<i>D</i> emissions from vehicle exhaust, which may mainly depend on TWC technology and exhaust temperature regime. This variability is suggestive of a δ<i>D</i> from traffic that varies over time, by season, and by geographical location. An earlier-derived integrated pure (end-member) δ<i>D</i> 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 δ<i>D</i> 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.
Creator (Dublin Core)
Vollmer, M. K.
Walter, S.
Bond, S. W.
Soltic, P.
Röckmann, T.
Date (Dublin Core)
2018-01-15
Type (Dublin Core)
Text
Format (Dublin Core)
application/pdf
Identifier (Dublin Core)
10.5194/acp-10-5707-2010
https://acp.copernicus.org/articles/10/5707/2010/
Source (Dublin Core)
eISSN: 1680-7324
Language (Dublin Core)
eng
