A sensitivity study of photolysis rate coefficients during POLARIS

Recent improvements in the agreement between observation-derived and modele d photolysis rate coefficients (j-values) have allowed for the close examin ation of the sensitivity of j-values to variations in physical parameters i nfluencing their magnitude and temporal/spatial variability. Altitude and s olar zenith angle profiles of j-values for two photolytic processes, NO2 -- > NO + O(P-3) and O-3 --> O-2 + O(D-1), are modeled, varying surface albedo , atmospheric baseheight, total column ozone, and ozone and temperature alt itude profiles over the ranges observed during the NASA Photochemistry of O zone Loss in the Arctic Region In Summer (POLARIS) high-altitude ER-2 aircr aft campaign. The effect of atmospheric refraction at high solar zenith ang les is also addressed. Modeled j-values using measured ozone/albedo input f rom the Composition and Photodissociative Flux Measurement (CPFM) spectrora diometer on board the ER-2 exceed those derived from CPFM flux measurements by 6% for jNO(2) and 14% for jO(3), within experimental uncertainties. The individual effects of albedo, baseheight, and ozone on j-values along spec ific ER-2 flight tracks are modeled and related to the temporal and spatial variability observed. For jNO(2), surface albedo has the greatest effect; for jO(3), the ozone above the aircraft and surface albedo are the most imp ortant.