THE DISTRIBUTION OF HYDROGEN, NITROGEN, AND CHLORINE RADICALS IN THE LOWER STRATOSPHERE - IMPLICATIONS FOR CHANGES IN O(3) DUE TO EMISSION OF NO(Y) FROM SUPERSONIC AIRCRAFT

In situ measurements of hydrogen, nitrogen, and chlorine radicals obta ined in the lower stratosphere during SPADE are compared to results fr om a photochemical model that assimilates measurements of radical prec ursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N2O5 agree well with measured concentrations of NO and ClO, but concentrations of HO2 and OH are underestimated by 10 to 25%, concentrations of NO2 are overestimated by 10 to 30%, and concentrati ons of HCl are overestimated by a factor of 2. Discrepancies for [OH] and [HO2] are reduced if we allow for higher yields of O(1D) from O3 p hotolysis and for heterogeneous production of HNO2. The data suggest m ore efficient catalytic removal of O3 by hydrogen and halogen radicals relative to nitrogen oxide radicals than predicted by models using re commended rates and cross sections. Increases in [O3] in the lower str atosphere may be larger in response to inputs of NO(y) from supersonic aircraft than estimated by current assessment models.