ESTIMATES OF THE TROPOSPHERIC LIFETIMES OF SHORT-LIVED AND LONG-LIVED ATMOSPHERIC POLLUTANTS

A computer model developed previously in our laboratory has been applied to substances with the potential for chemical reaction in the troposphere by two pathways: direct photolysis by sunlight and oxidation by hydroxyl radicals. A calculated value for the globally- and seasonally-averaged concentration of the hydroxyl radical is in reasonable agreement with previous reports. Compounds of the chlorobenzene, chlorobiphenyl and chlorophenol families are predicted to react with half-lives of several days at mid-latitudes. These lifetimes can be markedly dependent on season and on geographical location, showing the importance of using appropriate geographical and seasonal parameters to model the behaviour of pollutants in the atmosphere. Globally and seasonally averaged parameters have been used to estimate the tropospheric lifetimes of long-lived compounds such as chlorofluorocarbons.