A comparison of observations and model simulations of NOx/NOy in the lowerstratosphere

Extensive airborne measurements of the reactive nitrogen reservoir (NOy) an d its component nitric oxide (NO) have been made in the lower stratosphere. Box model simulations that are constrained by observations of radical and long-lived species and which include heterogeneous chemistry systematically underpredict the NOx (= NO + NO2) to NOy ratio. The model agreement is sub stantially improved if newly measured rate coefficients for the OH + NO2 an d OH + HNO3 reactions are used. When included in 2-D models, the new rate c oefficients significantly increase the calculated ozone loss due to NOx and modestly change the calculated ozone abundances in the lower stratosphere. Ozone changes associated with the emissions of a fleet of supersonic aircr aft are also altered.