Methyl chloride in the stratosphere

Abstract

There is much current interest in the chemistry of the stratosphere and the possible impact of chlorine compounds on the Earth's ozone layer. Profiles of anthropogenic compounds such as CFCl3 and CF2Cl2, which are emitted from aerosol spray cans, have already been measured in the stratosphere1. They confirm that substantial photolysis of these compounds is occurring and thereby releasing chlorine atoms which can catalyse ozone removal. The only natural chlorine containing compound which is likely to enter the stratosphere at significant concentrations is methyl chloride. It is therefore important that its profile be measured and compared with a computed profile to ascertain the likely impact on the ozone layer of naturally occurring chlorine. We report here measurements of the methyl chloride concentration profile up to an altitude of 32 km. The concentration falls off with altitude due to reaction with hydroxyl radicals and it confirms that chlorine of anthropogenic origin is now predominant in the stratosphere.