Understanding the kinetics of the ClO dimer cycle

M. von Hobe (1) , R. J. Salawitch (2) , T. Canty (2) , H. Keller-Rudek (3) , G. K. Moortgat (3) , J.-U. Grooss (1) , R. Müller (1) , F. Stroh (1)

1 FZJ - Forschungszentrum Jülich GmbH | Centre de recherche de Jülich | Jülich Research Centre
2 JPL - Jet Propulsion Laboratory
3 Atmospheric Chemistry Department [MPIC]

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).

Domaines: Océan, Atmosphère

M. von Hobe, R. J. Salawitch, T. Canty, H. Keller-Rudek, G. K. Moortgat, et al.. Understanding the kinetics of the ClO dimer cycle. Atmospheric Chemistry and Physics Discussions, 2006, 6 (4), pp.7905-7944. ⟨hal-00302069⟩