On the scavenging of SO2 by cloud and raindrops: III. A theoretical study of SO2 washout by rain falling through a pollution plume

Our previously described absorption model for the scavenging of trace gases by individual cloud and rain drops was applied to an ensemble of drops of given size distribution as found in typical atmospheric rainfalls. This study allowed: (1) determination of the redistribution which a pollution plume suffers as rain falls through it, and (2) determination of the amount of pollutant contained in. the fallen rain. For the present application it was assumed that the pollution plume consisted of SO₂, only, and that its concentration varied vertically as a Gaussian distribution centered 200 m above the ground. Rain of various intensities and corresponding drop size distributions was allowed to pass through this pollution layer.