PARTITIONING OF THE REACTIVE NITROGEN RESERVOIR IN THE LOWER STRATOSPHERE OF THE SOUTHERN-HEMISPHERE - OBSERVATIONS AND MODELING

Measurements of nitric oxide (NO), nitrogen dioxide (NO2), and total r eactive nitrogen (NOy = NO + NO2 + NO3 + HNO3 + ClONO2 + 2N(2)O(5) + . ..) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements fo r Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitude s. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO2 photolysis rate used in the SS approximation are reasonably accurate for conditions i n the lower stratosphere. However, NO2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self-consistency in our unders tanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model als o show good agreement with the NO and NO2 measurements, suggesting tha t the reactions affecting the partitioning of the NOy reservoir are we ll understood in the lower stratosphere.