Impact of Accurate Photolysis Calculations on the Simulation of Stratospheric Chemistry

Abstract

The interpretation of atmospheric measurements and the forecasting of the atmospheric composition require a hierarchy of accurate chemical transport and global circulation models. Here, the results of studies using Bremens Atmospheric Photochemical Model (BRAPHO) are presented. The focus of this study is given to the calculation of the atmospheric photolysis frequencies It is shown that the spectral high resolved simulation of the O2 Schumann–Runge bands leads to differences in the order of 10% in the calculated O2 photolysis frequency when compared with parameterizations used in other atmospheric models. Detailed treatment of the NO absorption leads to even larger differences (in the order of 50%) compared to standard parameterizations. Refraction leads to a significant increase in the photolysis frequencies at large solar zenith angles and, under polar spring conditions, to a significant change in the nighttime mixing ratio of some trace gases, e.g., NO3. It appears that recent changes in some important rate constants significantly alter the simulated BrOx- and HOx-budgets in the mid-latitude stratosphere.