3-DIMENSIONAL MODEL INTERPRETATION OF NOX MEASUREMENTS FROM THE LOWERSTRATOSPHERE

A three-dimensional off-line chemistry transport model, driven by Euro pean Centre for Medium-Range Weather Forecasts winds and temperatures, is used to interpret measurements of NO and NO2 taken from the DC-8 d uring the second Airborne Arctic Stratospheric Expedition. The model w as run in three configurations: gas phase chemistry alone, inclusion o f the N2O5 aerosol reaction, and inclusion of both N2O5 and ClONO2 aer osol reactions. The run including the N2O5 aerosol reaction alone usua lly agreed best with measured NOx/NOy ratios in midlatitude air masses . The NOx/NOy ratios of the run with both aerosol reactions were alway s too low, while the gas phase ratios were usually too high, especiall y during March. All three simulations generated extremely low NO2/NOy ratios in air parcels that had spent several days or more in the polar night. Measured NO2/NOy ratios in these types of air masses were some times equally low but could also be considerably higher. Observed NO/N O2 ratios differed strongly from known theory.