Atmos. Chem. Phys. Discuss., 6, 7905-7944, 2006
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Understanding the kinetics of the ClO dimer cycle
M. von Hobe1, R. J. Salawitch2, T. Canty2, H. Keller-Rudek3, G. K. Moortgat3, J.-U. Grooß1, R. Müller1, and F. Stroh1
1Forschungszentrum Jülich GmbH, Institute for Chemistry and Dynamics of the Geosphere (ICG-I), Jülich, Germany
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
3Max-Planck-Institute for Chemistry, Atmospheric Chemistry Division, Mainz, Germany

Abstract. Among the major factors controlling ozone loss in the polar winter is the kinetics of the ClO dimer catalytic cycle. The most important issues are the thermal equilibrium between ClO and Cl2O2, the rate of Cl2O2 formation, and the Cl2O2 photolysis rate. All these issues have been addressed in a large number of laboratory, field and theoretical studies, but large discrepancies between individual results exist and a self-consistent set of parameters compatible with field observations of ClO and Cl2O2 has not been identified. Here, we use thermodynamic calculations and unimolecular rate theory to constrain the ClO/Cl2O2 equilibrium constant and the rate constants for Cl2O2 formation and dissociation. This information is used together with available atmospheric data to examine Cl2O2 photolysis rates based on different Cl2O2 absorption cross sections. Good overall consistency is achieved using a ClO/Cl2O2 equilibrium constant recently suggested by Plenge et al. (2005), the Cl2O2 recombination rate constant reported by Nickolaisen et al. (1994) and Cl2O2 photolysis rates based on averaged absorption cross sections that are roughly intermediate between the JPL 2002 assessment and a laboratory study by Burkholder et al. (1990).

Citation: von Hobe, M., Salawitch, R. J., Canty, T., Keller-Rudek, H., Moortgat, G. K., Grooß, J.-U., Müller, R., and Stroh, F.: Understanding the kinetics of the ClO dimer cycle, Atmos. Chem. Phys. Discuss., 6, 7905-7944, doi:10.5194/acpd-6-7905-2006, 2006.
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