A MODEL FOR ESTIMATING THE RATE OF CHEMICAL TRANSFORMATION OF A VOC IN THE TROPOSPHERE BY 2 PATHWAYS - PHOTOLYSIS BY SUNLIGHT AND HYDROXYL RADICAL ATTACK

A simple model has been developed to describe the transformation of a tropospheric constituent by two competing pathways: direct photolysis and attack by hydroxyl radicals. The model makes use of the observations of Platt et al. (1988) that under the condition of low NO(x), the concentration of hydroxyl radicals appears to depend linearly on the rate of photolysis of ozone. It has been used to obtain a rapid but rought estimate of the rate of (photo)-chemical transformation of an organic tropospheric constituent and to estimate the tropospheric hydroxyl radical concentration under various conditions of geographical location, season, and time of day. In this work the model is used to describe the tropospheric chemistry of pentachlorophenol, but it is readily extended to other substances.