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| Titel |
Molecular hydrogen (H2) emissions and their isotopic signatures (H/D) from a motor vehicle: implications on atmospheric H2 |
| VerfasserIn |
M. K. Vollmer, S. Walter, S. W. Bond, P. Soltic, T. Röckmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 12 ; Nr. 10, no. 12 (2010-06-29), S.5707-5718 |
| Datensatznummer |
250008578
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| Publikation (Nr.) |
 copernicus.org/acp-10-5707-2010.pdf |
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| Zusammenfassung |
| Molecular hydrogen (H2), its isotopic signature (deuterium/hydrogen,
δD), 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.
H2 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 H2 ranged from δD = −140‰ to
δD = −195‰ upstream of the TWC but these values decreased to −270‰
to −370‰ after passing through the TWC. Post-TWC δD values for
the fuel-rich range showed a strong dependence on TWC temperature with more
negative δD for lower temperatures. These effects are attributed to
a rapid temperature-dependent H-D isotope equilibration between H2 and
water (H2O). In addition, post TWC δD in H2 showed a
strong dependence on the fraction of removed H2, suggesting isotopic
enrichment during catalytic removal of H2 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 δD emissions from vehicle exhaust, which may mainly
depend on TWC technology and exhaust temperature regime. This variability is
suggestive of a δD from traffic that varies over time, by season,
and by geographical location. An earlier-derived integrated pure (end-member) δD 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 δD 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. |
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