The fluorocarbon-ozone theory—II. Tropospheric lifetimes—an estimate of the tropospheric lifetime of CCl 3F

Abstract

Expected tropospheric CCl 3F concentrations as a function of time, eddy diffusion profile, and tropospheric lifetime have been calculated using production and release data presented earlier. The calculations are compared with the available experimental measurements of Lovelock, which have the advantage of continuous monitoring in the Northern Hemisphere since 1971, a substantial data base for the Southern Hemisphere, and data obtained on an extensive north-south cruise. The latter allow an analysis of the latitudinal dependence of CCl 3F concentrations, an analysis crucial in relating measurements at a given latitude to the global averages produced in model calculations. Data from other workers on CCl 3F concentrations, and earlier attempts at establishing experimental tropospheric lifetimes, are discussed. It is concluded that the most probable lifetime for CCl 3F, assuming the Hunten eddy diffusion profile, lies between 15 and 20 y. The analysis based on the Lovelock data is self-consistent, leaving mainly a question with regard to absolute calibration of the electron capture gas chromatography data. Changes in absolute calibration would lead to revisions in the estimated lifetimes. The data from other workers are, in general, consistent with the above conclusions. In particular, recent measurements from Washington State University and from Stanford Research Institute lead to 10–15 y lifetimes. Faster eddy diffusion than the Hunten scheme would lead to correspondingly longer calculated lifetimes.