Sensitivity of N2O, CFCl3, and CF2Cl2 two‐dimensional distributions to O2 absorption cross sections

The distribution of the trace gases N 2 O, CFCl 3 , and CF 2 Cl 2 is influenced by the O 2 absorption cross sections. There has been a recent indication in the literature that the O 2 cross sections used in past model studies may overestimate the true values. We have used a two‐dimensional model to perform a sensitivity study on the effects of changes in the O 2 cross sections on N 2 O, CFCl 3 , and CF 2 Cl 2 . Decreases in the O 2 cross sections between 180 and 230 nm resulted in altitude‐, latitude‐, and season‐dependent reductions in the computed species' concentrations. The altitude dependence of the reductions at mid‐latitudes agrees qualitatively with similar one‐dimensional model studies (Froidevaux and Yung, 1982; Brasseur et al., 1983). The vertical profiles of CFCl 3 are most affected and the vertical profiles of N 2 O are least affected by the O 2 cross‐section changes. The greatest changes in the trace gases occur above 20 km, at high latitudes, and in the winter. In general, the reduced O 2 cross sections led to better agreement between model calculations and experimental measurements for all three trace gases; however, there still remain some unexplained differences between observations and model predictions. This result implies that the reduced O 2 cross sections may be the better set. The accuracy of the lifetime calculations for the trace gases is not sufficient to recommend either set of O 2 cross sections. More precise measurements of O 2 absorption cross sections are thus required to determine the true values.