A sensitivity study of photolysis rate coefficients during POLARIS

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 yields NO + O(3P) and O3 yields O2 + O(1D), are modeled, varying surface albedo, atmospheric base height, 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 onboard the ER-2 exceed those derived from CPFM flux measurements by 6 percent for j(NO2) and 14 percent for j(O3), within experimental uncertainties. The individual effects of albedo, base height, and ozone on j-values along specific ER-2 flight tracks are modeled and related to the temporal and spatial variability observed. For j(NO2), surface albedo has the greatest effect; for j(O3), the ozone above the aircraft and surface albedo are the most important. (Author)