Modelling of radiation quantities and photolysis frequencies in the aqueous phase in the troposphere

In order to provide information about photolysis frequencies in the aqueous phase for chemical transport models including wet chemistry a parameterization which can be added to gaseous-phase photolysis models was developed. The actinic fluxes inside cloud droplets are calculated on the basis of rigorous Mie theory taking into account the effect of dissolved particulate aerosol material and 10 representative cloud droplet size distributions. The results show that the actinic flux inside cloud droplets are on the average more than twice as large as compared to the interstitial air. The newly developed parameterization has been applied together with the model STAR (System for Transfer of Atmospheric Radiation). Apart from the parameters influencing gas-phase photolysis frequencies the radiation quantities inside the cloud droplets and therefore the photolysis frequencies in the aqueous phase depend on the droplet size distribution, the mixing ratio of dry aerosol particulate material to c loud droplet water, and the amount of light absorbing material in the droplets. In-droplet radical source strengths have been calculated for the most important photolytic sources of OH and SO(4- ).