A size‐resolved model and a four‐mode parameterization of dry deposition of atmospheric aerosols

Abstract

To deposit on the ground surface, an airborne aerosol particle needs to pass through an aerodynamic resistance layer and a quasi‐laminar sublayer just adjacent to the surface. Traditionally, it is believed that the main mechanisms through which a particle overcomes the resistance from the quasi‐laminar sublayer are Brownian diffusion, interception, inertial impaction, and gravitational settling. In this study, a size‐resolved dry deposition model is formulated, which includes a new proposed dry deposition mechanism, the burst effect of eddy turbulence. The effects on dry deposition of particles by Brownian diffusion and inertial impaction are parameterized through the Schmidt number and the Stokes number, respectively. On the basis of the similarity between deposition of particles on walls of pipes and deposition of atmospheric particles on the ground surface, the burst effect of eddy turbulence is parameterized with the roughness Reynolds number. Through the roughness Reynolds number the effect on dry deposition by the surface roughness is parameterized into the model. Since the dry deposition velocity depends on particle size strongly, a four‐mode parameterization of dry deposition is proposed for use in atmospheric dispersion models. For each aerosol mode the parameterization of the bulk dry deposition velocity is made up of two terms: the Reynolds term and another term that is a power law function of friction velocity. The dry deposition velocities predicted by the model and the four‐mode parameterization are compared with the measurements reported in the literature, and good agreements are achieved.