A PHOTOCHEMICAL MODEL FOR THE SIMULATION OF THE VARIABILITY OF NITRIC-OXIDE AND NITROGEN-DIOXIDE AT SUNSET AND SUNRISE

A two-dimensional, stratospheric, photochemical model is constructed to simulate the variability of nitric oxide and nitrogen dioxide at sunset and sunrise for use in inversion algorithms which attempt to retrieve the concentration profiles of photochemically active species from satellite measurements. The model is applied for altitudes from 70 deg S to 70 deg N, and for altitudes from 10 km to 42 km; results for selected cases are presented, and are also compared to observations to show satisfactory agreement. The sensitivity of the inferred profiles of nitric oxide and nitrogen dioxide due to uncertainties in the used chemical rates, quantum yields, the temperature distribution and albedo are presented. The model provides a useful tool to adequately simulate the distribution of NO and NO2 at sunset and sunrise and also supports the understanding of chemical processes which are important for the abundance of stratospheric ozone.