1National Institute of Water and Atmospheric Research, Lauder, New Zealand
2Stiftung Alfred-Wegener Institut (AWI), Forschungsstelle Potsdam, Potsdam, Germany
3BC Consulting Ltd., Alexandra, New Zealand
4Stony Brook University, Stony Brook, New York, USA
5Department Atmosphere & Ocean Science, University of Maryland, Maryland, USA
6Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany
7Institute for Climate & Atmospheric Science, School of Earth & Environment, University of Leeds, Leeds, UK
8Freie Universität Berlin, Berlin, Germany
*now at: Bodeker Scientific, Alexandra, New Zealand
Received: 10 Sep 2010 – Discussion started: 04 Nov 2010
Abstract. Key kinetic parameters governing the partitioning of chlorine species in the Antarctic polar stratosphere were retrieved from 28 days of chlorine monoxide (ClO) microwave radiometer measurements made during the late winter/early spring of 2005 at Scott Base (77.85° S, 166.75° E). During day-time the loss of the ClO dimer chlorine peroxide (ClOOCl) occurs mainly by photolysis. Some time after sunrise, a photochemical equilibrium is established and the ClO/ClOOCl partitioning is determined by the ratio of the photolysis frequency, J, and the dimer formation rate, kf. The values of J and kf from laboratory studies remain uncertain to a considerable extent, and as a complement to these ongoing studies, the goal of this work is to provide a constraint on that uncertainty based on observations of ClO profiles in the Antarctic. First an optimal estimation technique was used to derive J/kf ratios for a range of Keq values. The optimal estimation forward model was a photochemical box model that takes J, kf, and Keq as inputs, together with a priori profiles of activated chlorine (ClOx = ClO+2×ClOOCl), profiles of ozone, temperature, and pressure. JPL06 kinetics are used as a priori in the optimal estimation and for all other chemistry in the forward model. Using the more recent JPL09 kinetics results in insignificant differences in the retrieved value of J/kf. A complementary approach was used to derive the optimal kinetic parameters; the full parameter space of J, kf, Keq and ClOx was sampled to find the minimum in differences between measured and modelled ClO profiles. Furthermore, values of Keq up to 2.0 times larger than recommended by JPL06 were explored to test the sensitivity of the J/kf ratio to changes in Keq. The results show that the retrieved J/kf ratios bracket the range of 1.23 to 1.97 times the J/kf value recommended by JPL06 over the range of Keq values considered. The retrieved J/kf ratios lie in the lower half of the large uncertainty range of J/kf recommended by JPL06 and towards the upper portion of the smaller uncertainty range recommended by JPL09.
Revised: 13 May 2011 – Accepted: 17 May 2011 – Published: 01 Jun 2011
Kremser, S., Schofield, R., Bodeker, G. E., Connor, B. J., Rex, M., Barret, J., Mooney, T., Salawitch, R. J., Canty, T., Frieler, K., Chipperfield, M. P., Langematz, U., and Feng, W.: Retrievals of chlorine chemistry kinetic parameters from Antarctic ClO microwave radiometer measurements, Atmos. Chem. Phys., 11, 5183-5193, doi:10.5194/acp-11-5183-2011, 2011.