Winds and convective mixing from a general circulation model of the atmosphere have been applied in a chemical tracer model (CTM) to simulate the global distribution and temporal variability of chlorofluorocarbons (CFCs). The seasonal cycle in moist convection, with maximum activity over continents in summer, leads to an annual cycle in the surface concentration of CFCs. Emissions are retained in the lowest levels of the atmosphere during winter, and surface concentrations peak near sources. In this season, CFCs from European sources are carried by low-level winds into the Arctic. During summer, vertical exchange is more efficient, and pollutants are transported more rapidly to the middle atmosphere. Consequently, concentrations of CFCs during summer are relatively low near the surface and elevated in the middle troposphere. Time series analysis of data from Adrigole, Ireland, indicates that the model accurately simulates long-range transport of air pollution. The model reproduces global distributions and trends for CFC-11 and CFC-12 observed by the ALE experiment; however, subgrid diffusion must be introduced into the model in order to reproduce the observed interhemispheric gradient. Interhemispheric exchange occurs mainly in the upper tropical troposphere, producing a profile which increases with altitude in the southern hemisphere, in agreement with observations. The distribution of CFCs is such that it is necessary to apply important corrections to observations at surface stations in order to derive global distributions.

A three-dimensional chemical tracer model for the troposphere is used to simulate the global distribution of ⁸⁵Kr, a long-lived radioisotope released at northern mid-latitudes by nuclear industry. Simulated distributions for the period 1980–1983 are in excellent agreement with data from six latitudinal profiles measured over the Atlantic. High concentrations of ⁸⁵Kr are predicted over the Arctic in winter, advected from European sources, and somewhat smaller enhancements arising from the same sources are predicted over the tropical Atlantic in summer. Latitudinal gradients are steepest in the northern tropics, with distinctly different seasonal variations over the Pacific, as compared to the Atlantic. The global inventory of ⁸⁵Kr is reconstructed for the period 1980–1983 by combining the concentrations measured over the Atlantic with the global distributions predicted by the model. The magnitude of the Soviet source is derived. The interhemispheric exchange time is calculated as 1.1 years, with little seasonal dependence.

A model for the photochemistry of the global troposphere constrained by observed concentrations of H₂O, O₃, CO, CH₄, NO, NO₂, and HNO₃ is presented. Data for NO and NO₂ are insufficient to define the global distribution of these gases but are nonetheless useful in limiting several of the more uncertain parameters of the model. Concentrations of OH, HO₂, H₂O₂, NO, NO₂, NO₃, N₂O₅, HNO₂, HO₂NO₂, CH₃O₂, CH₃OOH, CH₂O, and CH₃CCl₃ are calculated as functions of altitude, latitude, and season. Results imply that the source for nitrogen oxides in the remote troposphere is geographically dispersed and surprisingly small, less than 10⁷ tons N yr⁻¹. Global sources for CO and CH₄ are 1.5 × 10⁹ tons C yr⁻¹ and 4.5 × 10⁸ tons C yr⁻¹, respectively. Carbon monoxide is derived from combustion of fossil fuel (15%) and oxidation of atmospheric CH₄ (25%), with the balance from burning of vegetation and oxidation of biospheric hydrocarbons. Production of CO in the northern hemisphere exceeds that in the southern hemisphere by about a factor of 2. Industrial and agricultural activities provide approximately half the global source of CO. Oxidation of CO and CH₄ provides sources of tropospheric O₃ similar in magnitude to loss by in situ photochemistry. Observations of CH₃CCl₃ could offer an important check of the tropospheric model and results shown here suggest that computed concentrations of OH should be reliable within a factor of 2. A more definitive test requires better definition of release rates for CH₃CCl₃ and improved measurements for its distribution in the atmosphere.