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The potential impact of ClOx radical complexes on polar stratospheric ozone loss processes

by B Vogel, W Feng, M Streibel, R Mueller
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The importance of radical-molecule complexes for atmospheric chemistry\nhas been discussed in recent years. In particular, the existence of a\nClO center dot O-2 and ClOx water radical complexes like ClO center dot\nH2O, OClO center dot H2O, OClO center dot(H2O)(2), and ClOO center dot\nH2O could play a role in enhancing the ClO dimer (Cl2O2) formation and\ntherefore may constitute an important intermediate in polar\nstratospheric ozone loss cycles. Model simulations performed with the\nChemical Lagrangian Model of the Stratosphere (CLaMS) will be presented\nto study the role of radical complexes on polar stratospheric ozone loss\nprocesses. The model simulations are performed for the Arctic winter\n2002/2003 at a level of 500 K potential temperature and the results are\ncompared to observed ozone loss rates determined by the Match technique.\nMoreover, recently reported values for the equilibrium constant of the\nClO dimer formation are used to restrict the number of possible model\nresults caused by large uncertainties about radical complex chemistry.\nOur model simulations show that the potential impact of ClO center dot\nO-2 on polar ozone loss processes is small (dO(3)/ dt << 0.5\nppb/sunlight h) provided that the ClO center dot O-2 complex is only\nweakly stable. Assuming that the binding energies of the ClOx water\ncomplexes are much higher than theoretically predicted an enhancement of\nthe ozone loss rate by up to approximate to 0.5 ppb/sunlight h is\nsimulated. Because it is unlikely that the ClOx water complexes are much\nmore stable than predicted we conclude that these complexes have no\nimpact on polar stratospheric ozone loss processes. Although large\nuncertainties about radical complex chemistry exist, our findings show\nthat the potential impact of ClOx radical molecule complexes on polar\nstratospheric ozone loss processes is very small considering pure\ngas-phase chemistry. However the existence of ClOx radical-molecule\ncomplexes could possibly explain discrepancies for the equilibrium\nconstant of the ClO dimer formation found between recent laboratory and\nstratospheric measurements.

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