Forests as Sinks for Air Contaminants: Soil Compartment

Air contaminants may be removed from the atmosphere by a variety of mechanisms. The primary processes are precipitation scavenging, chemical reaction, dry deposition (sedimentation), and absorption (impaction) (Rasmussen et al., 1974). Loss via precipitation may occur in two ways: “rainout” which involves both absorption and particle capture by falling raindrops. Primary and secondary contaminants are subject to a large number of chemical reactions in the atmosphere that may ultimately transform them into an aerosol or oxidized or reduced product. Attachment by aerosols and subsequent deposition on the surface of the earth is termed dry deposition. Absorption by water bodies, soils, or vegetation at the surface of the earth is an additional extremely important removal process.