Retrievals of chlorine chemistry kinetic parameters from Ant

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TitleRetrievals of chlorine chemistry kinetic parameters from Antarctic ClO microwave radiometer measurementsAbstractKey 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 deg S, 166.75 deg 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+2xClOOCl), 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. © 2011 Author(s).AcknowledgementsWe thank Alan Parrish for his significant input in both the development of the ClO microwave radiometer and the initiation of the ground-based measurement program. We thank S. Wood, M. Kotkamp and Antarctica New Zealand for their help in maintaining the ClO microwave radiometer and their help in obtaining the ClO measurements. The ground-based measurement program is funded by NASA, grant NNX09AF40G. R. Schofield was funded by European Union (EU) project WaVES (MIF1-CT-2006-039646). The participation of R. Salawitch and T. Canty was supported by the NASA Aura and ACMAP programs. The SLIMCAT modelling work at Leeds was supported by NERC NCAS and the EU GEOMON project. S. Kremser thanks the German Academic Exchange Service (DAAD) for their support throughout the Doktorandenstipendium, which allowed this work to be conducted. We would like to thank Marc von Hobe and one anonymous reviewer for valuable comments and suggestions that contributed to a much improved manuscript following initial submission.

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1st AuthorKremser, S.AuthorKremser, S.Schofield, R.Bodeker, G.Connor, B.Rex, M.Barret, J.Mooney, T.Salawitch, R.Canty, T.Frieler, K.Chipperfield, M.Langematz, U.Feng, W.Year2011JournalAtmospheric Chemistry and PhysicsVolume11Number11Pages5183-5193DOI10.5194/acp-11-5183-2011URLhttps://www.scopus.com/inward/recor.....ca50727aae92ee574440f68f7Keywordsair temperatureatmospheric chemistryatmospheric pressurechlorine monoxidemicrowave radiometerozonepartitioningphotochemistryphotolysisreaction kineticsstratosphere, Antarctica, rank5

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TypeArticleCitationKremser, S., Schofield, R., Bodeker, G., Connor, B., Rex, M., Barret, J., Mooney, T., Salawitch, R., Canty, T., Frieler, K., Chipperfield, M., Langematz, U. and Feng, W. (2011). Retrievals of chlorine chemistry kinetic parameters from Antarctic ClO microwave radiometer measurements. Atmospheric Chemistry and Physics, 11(11): 5183-5193IdentifierKremser2011Relevancerank5