Simulation of the global CFC 11 using the Los Alamos chemical tracer model

Abstract

A three‐dimensional global chemical tracer model (CTM) with a multiyear circulation provided from the Los Alamos general circulation model (GCM) is developed to simulate the distributions and trends of global CFC 11 concentrations. Realistic geographic emission patterns and parameterized photolysis rates are included in the model. The initial condition corresponds to the observed values in July 1978. The results of six model years from July 1979 to June 1985 are presented. Comparisons with the Atmospheric Lifetime Experiment (ALE) observations show reasonable agreement. The intrinsic features of the five ALE sites can be summarized as follows: Adrigole is sensitive to horizontal diffusion because it is located between the European and North American sources; Samoa and Tasmania are heavily influenced by the interhemispheric transport; and Oregon and Barbados require a better resolved flow pattern to receive the transport from their nearest sources. The modeled global budget in terms of interhemispheric burden difference, stratospheric loss rate, interhemispheric transport, and its associated time constant is comparable with that derived from a previous study. A model sensitivity test using a large (∼3 times) horizontal diffusion shows that it modestly improves certain aspects of the simulations at southern hemisphere ALE sites, however, at the cost of a greatly reduced interhemispheric burden difference and exchange time constant.