Use of a Lennard-Jones calculation for estimation of molecular diffusivity of gases like SO2 for use in scavenging models is recommended. A profile of molecular diffusivity of SO2 in air through the PBL is obtained. Results indicate a change of about 17.5% between the diffusivity values at the surface and at the top of the PBL. The possible changes that could result in scavenging model calculations due to this change are also discussed. © 1986 D. Reidel Publishing Company.