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| Titel |
Understanding the kinetics of the ClO dimer cycle |
| VerfasserIn |
M. Hobe, R. J. Salawitch, T. Canty, H. Keller-Rudek, G. K. Moortgat, J.-U. Grooß, R. Müller, F. Stroh |
| 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 ; 7, no. 12 ; Nr. 7, no. 12 (2007-06-15), S.3055-3069 |
| Datensatznummer |
250005079
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| Publikation (Nr.) |
 copernicus.org/acp-7-3055-2007.pdf |
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| Zusammenfassung |
| Among the major factors controlling ozone loss in the polar vortices in
winter/spring is the kinetics of the ClO dimer catalytic cycle. Here, we
propose a strategy to test and improve our understanding of these kinetics by
comparing and combining information on the thermal equilibrium between ClO
and Cl2O2, the rate of Cl2O2 formation, and the
Cl2O2 photolysis rate from laboratory experiments, theoretical
studies and field observations. Concordant with a number of earlier studies,
we find considerable inconsistencies of some recent laboratory results with
rate theory calculations and stratospheric observations of ClO and
Cl2O2. The set of parameters for which we find the best overall
consistency – namely the ClO/Cl2O2 equilibrium constant suggested
by Plenge et al. (2005), the Cl2O2 recombination rate constant
reported by Nickolaisen et al. (1994) and Cl2O2 photolysis rates
based on absorption cross sections in the range between the JPL 2006
assessment and the laboratory study by Burkholder et al. (1990) – is not
congruent with the latest recommendations given by the JPL and IUPAC panels
and does not represent the laboratory studies currently regarded as the most
reliable experimental values. We show that the incorporation of new Pope et
al. (2007) Cl2O2 absorption cross sections into several models,
combined with best estimates for other key parameters (based on either JPL
and IUPAC evaluations or on our study), results in severe model
underestimates of observed ClO and observed ozone loss rates. This finding
suggests either the existence of an unknown process that drives the
partitioning of ClO and Cl2O2, or else some unidentified problem
with either the laboratory study or numerous measurements of atmospheric ClO.
Our mechanistic understanding of the ClO/Cl2O2 system is grossly
lacking, with severe implications for our ability to simulate both present
and future polar ozone depletion. |
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