A two‐dimensional photochemical model of the atmosphere: 2. The tropospheric budgets of the anthropogenic chlorocarbons CO, CH4, CH3Cl and the effect of various NOx sources on tropospheric ozone

Abstract

This paper presents two‐dimensional photochemical model simulations that show the influence of the various NOx sources from industry, lightning, the stratosphere, and aircraft on the tropospheric distributions of NOx, HNO3, and O3. We found that, by far, the best agreement with the global observations is obtained if the industrial sources are included in the calculations. Industrial activities have led to substantial increases of ozone concentrations in the lower troposphere of the northern hemisphere. Emissions of NOx by high‐flying aircraft have only a small effect on ozone concentrations in the troposphere. The ability of the model to simulate the global distributions of the long‐lived chlorocarbons CFCl3 and CF2Cl2 indicates that the interhemispheric exchange is rather well described. The model confirms an earlier finding by Rowland et al. (1982) that the CF2Cl2 emission rates estimated by the Chemical Manufacturers Association (CMA) may be 35–40% lower for the period 1976 through 1980. The model also supports the earlier finding of Hyson et al. (1980) that CFCl3 is apparently increasing roughly 10% faster than the CMA emission rates can account for during the period 1976 through 1980. Although this disparity could be explained by assuming 10% higher emission rates for CFCl3 during the period, the behavior of the interhemispheric gradient indicates that errors in the determination of the absolute concentrations could also be an explanation. The ability of the model to simultaneously simulate measured distributions of the shorter‐lived chlorocarbons CH3CCl3, CH2Cl2, C2HCl3, and C2Cl4 indicates that its average OH concentrations are also about correct. Based on these OH concentrations, the model tropospheric budgets of CO, CH4, and CH3Cl are calculated. The computed losses of CO, CH4, and CH3Cl by reaction with OH are 2.1×1015 g CO yr−1, 3.2×1014 g CH4 yr−1, and 1.9× 012 g CH3Cl yr−1, respectively.