A sensitivity study of photolysis rate coefficients during POLARIS

Abstract

Recent improvements in the agreement between observation-derived and modeled photolysis rate coefficients (j-values) have allowed for the close examination of the sensitivity of j-values to variations in physical parameters influencing their magnitude and temporal/spatial variability. Altitude and solar zenith angle profiles of j-values for two photolytic processes, NO2 → NO + O(3P) and O3 → O2 + O(1D), are modeled, varying surface albedo, atmospheric baseheight, total column ozone, and ozone and temperature altitude profiles over the ranges observed during the NASA Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) high-altitude ER-2 aircraft campaign. The effect of atmospheric refraction at high solar zenith angles is also addressed. Modeled j-values using measured ozone/albedo input from the Composition and Photodissociative Flux Measurement (CPFM) spectroradiometer on board the ER-2 exceed those derived from CPFM flux measurements by 6% for jNO2 and 14% for jO3, within experimental uncertainties. The individual effects of albedo, baseheight, and ozone on j-values along specific ER-2 flight tracks are modeled and related to the temporal and spatial variability observed. For jNO2, surface albedo has the greatest effect; for jO3, the ozone above the aircraft and surface albedo are the most important. Copyright 1999 by the American Geophysical Union.