1Institute of Energy and Climate Research: Stratosphere (IEK-7), Forschungszentrum Jülich GmbH, Jülich, Germany
2Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany
3Department of Physics, University of Wuppertal, Germany
4Institute for Physics of the Atmosphere, Johannes Gutenberg Universität Mainz, Germany
5Particle Chemistry Department, Max Planck-Institute für Chemie, Mainz, Germany
Abstract. The photolysis frequency of dichlorine peroxide (ClOOCl) JClOOCl is a critical parameter in catalytic cycles destroying ozone in the polar stratosphere. In the atmospherically relevant wavelength region, published laboratory measurements of ClOOCl absorption cross sections and spectra are not in good agreement, resulting in significant discrepancies in JClOOCl. Previous investigations of the consistency with atmospheric observations of ClO and ClOOCl have focused on the photochemical equilibrium between ClOOCl formation and photolysis, and thus could only constrain the ratio of JClOOCl over the rate constant of the ClO recombination reaction krec. Here, we constrain the atmospherically effective JClOOCl independent of krec using ClO data sampled in the same air masses before and directly after sunrise. Over sunrise, when the ClO/ClOOCl system comes out of thermal equilibrium and the influence of the ClO recombination reaction is negligible, the rise in ClO concentration is significantly faster than expected from JClOOCl based on the absorption spectrum proposed by Pope et al. (2007), but does not warrant cross sections larger than recently published values by Papanastasiou et al. (2009). In particular, the existence of a significant ClOOCl absorption band longwards of 420 nm, is effectively ruled out by our observations. Additionally, the night-time ClO observations show that the ClO/ClOOCl thermal equilibrium constant can not be significantly higher than the one proposed by Plenge et al. (2005).