The process of scavenging below-cloud pollutants (SO₂, H₂O₂, O₃, NH₃, CO₂)by raindrops is studied,based on a physico-chemical model. Besides the aqueous oxidatiom of S(Ⅳ) by H₂O₂ and O₃,the catalyic oxidations of S(Ⅳ) by Fe³⁺ and Mn²⁺ in thefalling drops are also considered. Results indicate: (1)the[SO₄^2-] and pH spectra can bede developed; (2)the scavenging process below clouds is influenced by a number of factors: initial concentration of pollutants in the raindrops,precipitation intensity and NH₃ concentration, and (3) this study can be uded for explaining some phenomena observedfrom field measurements.