Annales Geophysicae
ISSN: 0992-7689 aprinted version)
ISSN: 1432-0576 aelectronic version)
Abstract Volume 13 Issue 4 a1995) pp 406-412
Estimation of heterogeneous reaction rates for stratospheric trace gases
with particular reference to the diffusional uptake of HCl and ClONO2 by
polar stratospheric clouds
S. Ghosh, D. Lary, J. A. Pyle
Centre for Atmospheric Science, Department of Chemistry, Lensfield Road, Cambridge CB2 1EW, England
Received: 1 June 1994/Revised: 13 September 1994/Accepted: 17 October 1994
Abstract. The stratosphere holds a variety of particulates like polar stratospheric clouds aPSCs) and sulphate aerosols which
catalyse chemical reactions. These reactions cause changes in the composition of the stratosphere, including the redistribution of
active chlorine which might lead to ozone destruction. As a result during recent years a lot of effort has been directed towards the
quantification of the uptake of trace gases like ClONO2, HCl, etc. into these particulates. However, it has been observed that
many of the two and three dimensional models used in such studies are constrained by the lack of adequate rate constant data.
This paper describes a theoretical approach to estimate the reaction rate constants for 23 gases on both types of polar
stratospheric clouds atype I and II). It is found that for gases like N2O5, ClONO2 and HCl, diffusional uptake is important and
contributes significantly to the heterogeneous reaction rate. A complete Lennard-Jones calculation is used to accurately compute
the trace gas diffusion coefficients.
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