MEASUREMENTS OF PEROXIDES IN THE ATMOSPHERE AND THEIR RELEVANCE TO THE UNDERSTANDING OF GLOBAL TROPOSPHERIC CHEMISTRY

Peroxides are produced as termination products in atmospheric chain re actions involving peroxy radicals, both organic and inorganic. They ar e the principal sink for radicals produced in the troposphere from the photolysis of ozone in the presence of water vapour and as such are e xcellent indicators of the extent of free radical chemistry taking pla ce at any given location. Their measurement is relatively simple and d ata on the concentration of peroxides in the atmosphere with respect t o time and space can be collected easily and extensively. New data on peroxide measurements collected at different parts of the atmosphere, principally by the Meteorological Office C-130 Hercules aircraft are p resented. They indicate that the extent of hydroxyl radical chemistry during the summer is controlled mostly by the water vapour content of the atmosphere. Both negative and positive correlations are observed b etween ozone and peroxide concentrations in vertical profiles over the North Atlantic Ocean and the equatorial Pacific. The negative correla tions demonstrate that the ozone concentration throughout the troposph ere is determined mostly by in situ photochemistry. This is borne out by the close correlation between calculated and measured concentration s of peroxides in vertical profiles. Positive correlations over the No rth Atlantic allow us to make an estimate of the amount of ozone, pres ent there in the summer, which is formed from tropospheric as opposed to stratospheric chemistry.