Clouds play a major role in the production of oxidants and acids in the atmosphere.
Recent research has shown that clouds also affect tropospheric ozone concentrations on a global basis. Because clouds serve as sinks for many species that produce ozone and because of their affects on the photolysis of nitrogen dioxide and other species it appears that clouds reduce tropospheric ozone on a global basis. Improved cloud models are needed to better understand acid deposition and tropospheric ozone. A cloud is a very complex chemical processor with many different physical and chemical processes. The cloud receives trace gases from its inflow region, its vertical winds redistributes the gases and the cloud transforms the gases through gas and aqueous-phase chemistry.