A simple parameterization of the diurnally varying planetary boundary layer (PBL) is developed for use in global scale dispersion and air chemistry models. The parameterization captures the essential features of the convective and stable boundary layers and includes the effects of surface and volumetric sources of pollutants and trace gases. Initial tests are performed with a one-dimensional model. These tests show that the parameterization is mass conserving and gives realistic results. The volumetric source term can be used to model photochemical production of ozone in the convective PBL, and the surface source term can be used to model emissions such as radon or methane. ¿ American Geophysical Union 1994