Partitioning of the reactive nitrogen reservoir in the lower stratosphere of the southern hemisphere: Observations and modeling

Abstract

Measurements of nitric oxide (NO), nitrogen dioxide (NO 2 ), and total reactive nitrogen (NO y = NO + NO 2 + NO 3 + HNO 3 + ClONO 2 + 2N 2 O 5 + …) were made during austral fall, winter, and spring 1994 as part of the NASA Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft mission. Comparisons between measured NO 2 values and those calculated using a steady state (SS) approximation are presented for flights at mid and high latitudes. The SS results agree with the measurements to within 8%, suggesting that the kinetic rate coefficients and calculated NO 2 photolysis rate used in the SS approximation are reasonably accurate for conditions in the lower stratosphere. However, NO 2 values observed in the Concorde exhaust plume were significantly less than SS values. Calculated NO 2 photolysis rates showed good agreement with values inferred from solar flux measurements, indicating a strong self‐consistency in our understanding of UV radiation transmission in the lower stratosphere. Model comparisons using a full diurnal, photochemical steady state model also show good agreement with the NO and NO 2 measurements, suggesting that the reactions affecting the partitioning of the NO y reservoir are well understood in the lower stratosphere.