The distribution of hydrogen, nitrogen, and chlorine radicals in the lower stratosphere: Implications for changes in O₃ due to emission of NO_y from supersonic aircraft

Abstract

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained in the lower stratosphere during SPADE are compared to results from a photochemical model that assimilates measurements of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N 2 O 5 agree well with measured concentrations of NO and ClO, but concentrations of HO 2 and OH are underestimated by 10 to 25%, concentrations of NO 2 are overestimated by 10 to 30%, and concentrations of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO 2 ] are reduced if we allow for higher yields of O( 1 D) from O 3 photolysis and for heterogeneous production of HNO 2 . The data suggest more efficient catalytic removal of O 3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using recommended rates and cross sections. Increases in [O 3 ] in the lower stratosphere may be larger in response to inputs of NO y from supersonic aircraft than estimated by current assessment models.