Journal of Atmospheric Chemistry 25: 167-199, 1996. 167 © 1996 Kluwer Academic Publishers. Printed in the Netherlands. Two-Dimensional Modelling of Some CFC Replacement Compounds OLIVER WILD,* OLIVER V. RATFIGAN,** RODERIC L. JONES, JOHN A. PYLE and R. ANTHONY COX Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge CB2 I EW, U.K. (Received: 2 November 1995; in final form: 17 June 1996) Abstract. The Cambridge 2-D Eulerian model has been used to study the potential atmospheric distributions and lifetimes of a number of CFC replacement compounds and their degradation prod- ucts. The study has focused on I-IFC 134a and HCFCs 123, 141b and 142b and the major products formed by their atmospheric degradation. The loss of these compounds and their products by hydrox- yl radical attack, photolysis and in-cloud hydrolysis have been investigated. The study has shown that HCFCs 141b and 142b have sufficiently long lifetimes to enter the stratosphere in significant quantities, where degradation leads to an increase in the total stratospheric chlorine concentration. The study has also highlighted areas where further experimental work would be valuable, in partic- ular characterisation of the product channels for the degradation reactions and deter'ruinationof the removal rates of the products in the aqueous phase. Key words: CFC replacement compounds, distributions, tropospheric lifetimes, trifluoroacetic acid. 1. Introduction Since their discovery in the late 1930s chlorofluorocarbons (CFCs) have been used extensively both in industry and domestically as refrigerants, solvents and propellants. Their physical properties and volatility make them ideal for these purposes, and their chemically inert nature makes them safe for everyday use. However, a number of studies over the past few years have indicated that the heavy use of these compounds has been responsible for a significant build up of chlorine in the lower stratosphere, and that this is one of the major factors in the observed depletion of ozone in the polar lower stratosphere (Farman et aL, 1985; SORG, 1993). A number of substitute compounds have been proposed with simi- lar physical properties (WMO, 1989), but with little or no effect on stratospheric chlorine or ozone levels. The most important of these are the hydrochlorofluorocar- bons (HCFCs) and hydrofluorocarbons (HFCs). These compounds are preferable to CFCs as they contain at least one hydrogen atom which is susceptible to hydrox- yl attack in the troposphere, and consequently a smaller proportion reaches the stratosphere. The HFCs are particularly important, as they do not contain chlorine, * Now at: Earth System Science, University of California, Irvine CA 92697. ** Now at: Department of Chemistry, Boston College, Boston MA 02167.