Diffusion Model for a Convective Layer. Part II: Plume Released from a Continuous Point Source

Abstract

A two-dimensional diffusion model for a convective planetary boundary layer is presented. Three prognostic equations are employed for the concentration, the concentration flux, and the covariance of temperature and concentration. The environmental background, which includes the mean wind, the mean virtual potential temperature, the turbulent kinetic energy and other second moments, is generated from Part I of this study. For an elevated point source, the plume concentration centerline descends until it intercepts the ground, then it rebounds and returns to the mixed layer, while the material released from a surface point source gradually ascends into the mixed layer, carried aloft by the updrafts of the convective motion. Compared to the laboratory and field experiments, this model simulates well the diffusion of passive pollutants released from a continuous point source into the convective layer.