Comparison of modeled and observed values of NO₂ and JNO₂ 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 spring, early summer, and late summer in the Arctic region during 1997 as part of the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) field campaign. In the sunlit atmosphere, NO2 and NO are in steady state through NO2 photolysis and reactions involving O-3, ClO, BrO, and HO2. By 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 this dependence could not be identified. Overall, the mean linear fits in the various comparisons show agreement within 19%, well within the combined uncertainties (+/-50 to 70%). These results suggest that photochemistry controlling the NO2/NO abundance ratio is well represented throughout much of the sunlit lower stratosphere. A reduction in the uncertainty of laboratory determinations of the rate coefficient of NO + O-3 --> NO2 + O-2 would aid future analyses of these or similar atmospheric observations.