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| Titel |
A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation |
| VerfasserIn |
G. Pieterse, M. C. Krol, 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 ; 9, no. 21 ; Nr. 9, no. 21 (2009-11-09), S.8503-8529 |
| Datensatznummer |
250007740
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| Publikation (Nr.) |
 copernicus.org/acp-9-8503-2009.pdf |
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| Zusammenfassung |
| The isotopic composition of molecular hydrogen (H2) produced by
photochemical oxidation of methane (CH4) and Volatile Organic Compounds
(VOCs) is a key quantity in the global isotope budget of (H2). The many
individual reaction steps involved complicate its investigation. Here we
present a simplified structure-activity approach to assign isotope effects to
the individual elementary reaction steps in the oxidation sequence of
CH4 and some other VOCs. The approach builds on and extends the work by
Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and
allows the application, in principle, also to other compounds. The idea is
that the C-H and C-D bonds – seen as reactive sites – have similar relative
reaction probabilities in isotopically substituted, but otherwise identical
molecules. The limitations of this approach are discussed for the reaction
CH4+Cl. The same approach is applied to VOCs, which are important
precursors of H2 that need to be included into models. Unfortunately,
quantitative information on VOC isotope effects and source isotope signatures
is very limited and the isotope scheme at this time is limited to a strongly
parameterized statistical approach, which neglects kinetic isotope effects.
Using these concepts we implement a full hydrogen isotope scheme in a
chemical box model and carry out a sensitivity study to identify those
reaction steps and conditions that are most critical for the isotope
composition of the final H2 product. The reaction scheme is directly
applicable in global chemistry models, which can thus include the isotope
pathway of H2 produced from CH4 and VOCs in a consistent way. |
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