 |
| Titel |
Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air |
| VerfasserIn |
S. J. Allin, J. C. Laube, E. Witrant, J. Kaiser, E. McKenna, P. Dennis, R. Mulvaney, E. Capron, P. Martinerie, T. Röckmann, T. Blunier, J. Schwander, P. J. Fraser, R. L. Langenfelds, W. T. Sturges |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 12 ; Nr. 15, no. 12 (2015-06-23), S.6867-6877 |
| Datensatznummer |
250119846
|
| Publikation (Nr.) |
 copernicus.org/acp-15-6867-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| The stratospheric degradation of chlorofluorocarbons (CFCs) releases
chlorine, which is a major contributor to the destruction of stratospheric
ozone (O3). A recent study reported strong chlorine isotope
fractionation during the breakdown of the most abundant CFC (CFC-12,
CCl2F2, Laube et al., 2010a), similar to effects seen in nitrous
oxide (N2O). Using air archives to obtain a long-term record of chlorine
isotope ratios in CFCs could help to identify and quantify their sources and
sinks. We analyse the three most abundant CFCs and show that CFC-11
(CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant
stratospheric chlorine isotope fractionation, in common with CFC-12. The
apparent isotope fractionation (ϵapp) for mid- and
high-latitude stratospheric samples are respectively −2.4 (0.5) and −2.3 (0.4) ‰ for CFC-11,
−12.2 (1.6) and −6.8 (0.8) ‰ for CFC-12 and
−3.5 (1.5) and −3.3 (1.2) ‰ for CFC-113, where the number in parentheses
is the numerical value of the standard uncertainty expressed in per mil. Assuming a constant isotope
composition of emissions, we calculate the expected trends in the
tropospheric isotope signature of these gases based on their stratospheric
37Cl enrichment and stratosphere–troposphere exchange. We compare these
projections to the long-term δ (37Cl) trends of all three CFCs,
measured on background tropospheric samples from the Cape Grim air archive
(Tasmania, 1978–2010) and tropospheric firn air samples from Greenland
(North Greenland Eemian Ice Drilling (NEEM) site) and Antarctica (Fletcher
Promontory site). From 1970 to the present day, projected trends agree with
tropospheric measurements, suggesting that within analytical uncertainties, a
constant average emission isotope delta (δ) is a compatible scenario.
The measurement uncertainty is too high to determine whether the average
emission isotope δ has been affected by changes in CFC manufacturing
processes or not. Our study increases the suite of trace gases amenable to
direct isotope ratio measurements in small air volumes (approximately
200 mL), using a single-detector gas chromatography–mass spectrometry
(GC–MS) system. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|