Comparison of modeled and observed values of NO2 and JNO(2) during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission

Stratospheric measurements of NO, NO2, O-3, ClO, and HO2 were made during s pring, early summer, and late summer in the Arctic region during 1997 as pa rt of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLA RIS) field campaign. In the sunlit atmosphere, NO2 and NO are in steady sta te through NO2 photolysis and reactions involving O-3, ClO, BrO, and HO2. B y combining observations of O-3, ClO, and HO2, observed and modeled values of the NO2 photolysis rate coefficient ((NO2)-N-J), and model estimates of BrO, several comparisons are made between steady state and measured values of both NO2 and (NO2)-N-J An apparent seasonal dependence in discrepancies between calculated and measured values was found; however, a source for thi s dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined unc ertainties (+/-50 to 70%). These results suggest that photochemistry contro lling the NO2/NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory de terminations of the rate coefficient of NO + O-3 --> NO2 + O-2 would aid fu ture analyses of these or similar atmospheric observations.