Numerical study of cloud effects on tropospheric ozone

An elaborate cloud chemistry box model has developed in which gaseous-phase photochemistry is coupled with aqueous-phase chemistry to investigate the variation of ozone concentration and its distribution features above and be low cloud, and in its upper and lower part, with results compared to observ ations. The cloud chemistry model is composed of three parts: gaseous-phase chemistry, aqueous-phase chemistry, and scavenging of soluble gases. The c loud influence on the ozone concentration can be separated into three porti ons: 1) the change of solar radiation flux by cloud which is responsible fo r decreasing or increasing of photochemical reaction in the troposphere and thus reducing or enhancing the concentration; 2) direct absorption of ozon e and its precursors (NOx, NMHC, free radicals, etc.) by in-cloud liquid wa ter; 3) aqueous-phase chemical reaction happening to species absorbed by cl oud, responsible for the change in gaseous-phase ozone concentration. Numer ical simulations show substantial difference in the importance regarding th e effect of these factors on ozone between these levels and a close relatio n of cloud physical structure to the factors. The results agree well with t he observations.