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| Titel |
The isotopic composition of methane in the stratosphere: high-altitude balloon sample measurements |
| VerfasserIn |
T. Röckmann, M. Brass, R. Borchers, A. Engel |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2011-12-21), S.13287-13304 |
| Datensatznummer |
250010303
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| Publikation (Nr.) |
 copernicus.org/acp-11-13287-2011.pdf |
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| Zusammenfassung |
| The isotopic composition of stratospheric methane has been
determined on a large suite of air samples from stratospheric balloon
flights covering subtropical to polar latitudes and a time period of 16 yr.
154 samples were analyzed for δ13C and 119
samples for δD, increasing the previously published dataset for
balloon borne samples by an order of magnitude, and more than doubling the
total available stratospheric data (including aircraft samples) published to
date. The samples also cover a large range in mixing ratio from tropospheric
values near 1800 ppb down to only 250 ppb, and the strong isotope
fractionation processes accordingly increase the isotopic composition up to
δ13C = −14‰ and δD = +190‰, the largest
enrichments observed for atmospheric CH4 so far. When
analyzing and comparing kinetic isotope effects (KIEs) derived from single balloon
profiles, it is necessary to take into account the residence time in the
stratosphere in combination with the observed mixing ratio and isotope
trends in the troposphere, and the range of isotope values covered by the individual
profile. The isotopic composition of CH4 in the stratosphere is affected by
both chemical and dynamical processes. This severely hampers interpretation of
the data in terms of the relative fractions of the three important sink
mechanisms (reaction with OH, O(1D) and Cl). It is shown that a formal sink
partitioning using the measured data severely
underestimates the fraction removed by OH, which is likely due to the
insensitivity of the measurements to the kinetic fractionation in the lower
stratosphere. Full quantitative interpretation of the CH4
isotope data in terms of the three sink reactions requires a global model. |
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