8 The Kinetics of the ClO-Dimer Cycle

Monday, 11 January 2016
Ross J. Salawitch, University of Maryland, College Park, MD; and T. Canty

The Kinetics of the ClO-Dimer Cycle

Molina and Molina (JPC, 1987) first proposed that the ClO-dimer cycle would be an important route for the catalytic removal of stratospheric ozone. Here, we use a photochemical model of halogen chemistry, constrained by in-situ aircraft observations of [ClO] and [ClOOCl], to test our understanding of the kinetics of this cycle. We will show simulations of daytime observations for a variety of laboratory determinations of the rate constant for formation of ClOOCl via the self-reaction of ClO as well as for the absorption cross section of ClOOCl (σClOOCl). Nighttime observations of [ClO] and [ClOOCl] will be compared to simulations based on various laboratory and theoretical determinations of the ClO/ClOOCl equilibrium constant. Our analysis suggests ClOOCl photolyzes more quickly than inferred from the most recent laboratory determination of the σClOOCl (Young et al., GRL, 2014), which is the first study to span all wavelengths relevant for atmospheric photolysis. We also show gaps remain in our understanding of the nighttime partitioning of [ClO] and [ClOOCl], for cold conditions typical of the polar lower stratosphere during winter.

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