Residence time of atmospheric pollutants as dependent on source characteristics, atmospheric diffussion processes and sink mechanisms

A brief discussion of the sink mechanisms of atmospheric pollutants is given and particular emphasis is given to the relative importance of rain-out (wash-out) and dry deposition. The turbulent transfer processes that determine the latter are analyzed in the light of the classical theory for the atmospheric surface boundary layer. The transfer rates to the free atmosphere (where rain-out and wash-out are the sink mechanisms) and to the earth’s surface (when dry deposition occurs) are computed as dependent on height of emission, roughness of the earth’s surface, deposition velocity (or accommodation efficiency) at the earth’s surface and the intensity of the turbulent processes (as dependent on wind velocity). On the basis of such computations the residence time of atmospheric pollutants are computed and the article concludes with a discussion of the relative importance of rain-out (wash-out) and dry deposition in this regard.