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| Titel |
Stable carbon isotope fractionation in the UV photolysis of CFC-11 and CFC-12 |
| VerfasserIn |
A. Zuiderweg, J. Kaiser, J. C. Laube, T. Röckmann, R. Holzinger |
| 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 ; 12, no. 10 ; Nr. 12, no. 10 (2012-05-16), S.4379-4385 |
| Datensatznummer |
250011156
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| Publikation (Nr.) |
 copernicus.org/acp-12-4379-2012.pdf |
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| Zusammenfassung |
| The chlorofluorocarbons CFC-11 (CFCl3) and CFC-12 (CF2Cl2)
are stable atmospheric compounds that are produced at the earth's surface,
but removed only at high altitudes in the stratosphere by photolytic
reactions. Their removal liberates atomic chlorine that then catalytically
destroys stratospheric ozone. For such long-lived compounds, isotope effects
in the stratospheric removal reactions have a large effect on their global
isotope budgets. We have demonstrated a photolytic isotope fractionation for
stable carbon isotopes of CFC-11 and CFC-12 in laboratory experiments using
broadband UV-C (190–230 nm) light. 13C/12C isotope fractionations
(ε) range from (−23.8±0.9) to (−17.7±0.4) ‰ for CFC-11 and
(−66.2±3.1) to (−51.0±2.9) \permil for CFC-12 between 203 and 288 K, a
temperature range relevant to conditions in the troposphere and
stratosphere. These results suggest that CFCs should become strongly
enriched in 13C with decreasing mixing ratio in the stratosphere,
similar to what has been recently observed for CFC chlorine isotopes. In
conjunction with the strong variations in CFC emissions before and after the
Montréal Protocol, the stratospheric enrichments should also lead to a
significant temporal increase in the 13C content of the CFCs at the
surface over the past decades, which should be recorded in atmospheric air
archives such as firn air. |
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