Dry deposition

5.2.1 Dry deposition of aerosol particles

The removal of aerosol particles under dry weather conditions is caused by turbulent diffusion and gravitational sedimentation, which transport particles to the Earth's surface, as well as by impaction on vegetation, buildings and other objects. Turbulent diffusion itself does not remove particles (Twomey, 1977). Soil and other surfaces are bordered by a thin laminar layer (~ 1 mm thick) across which particles must be transported by other processes (e.g. phoretic forces, molecular diffusion, sedimentation).

Disregarding impaction, dry removal of aerosol particles can be described formally by the following equation (e.g. Makhonyko, 1966):

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