A Parameterization of Diffusion into the Mixed Layer

Abstract

The diffusion from a source near the ground into the daytime mixed layer has been deduced from laboratory measurements, making use of boundary-layer free-convection similarity scaling. A parameterization is presented which preserves this similarity scaling for intermediate and long-range diffusion, and which for short-range diffusion incorporates the effects of source height and of near-ground mechanically induced mixing. The parameterization can be applied in steady conditions to the pollution concentration downwind of a steady source, or in unsteady conditions to the concentration in an expanding cylindrical column advected within a multiple puff model. The parameterization applies only to chemically inert, nonbuoyant pollutants having no interaction with the ground.