A large eddy simulation of buoyant and non-buoyant plume dispersion in the atmospheric boundary layer

Abstract

The dispersion of contaminants in the convective atmospheric boundary layer is calculated with the aid of a large eddy model. Our initial condition is a model simulation of the quasi-stationary convective boundary layer in a horizontal calculation domain of 5 × 5 km. At t = 0 we introduce in this boundary layer an instantaneous line source of contaminants. Subsequently, we calculate the evolution of the line source by integrating the conservation equation of the contaminant simultaneously with the other governing equations of our large eddy model. We consider both a source of passive material with release heights of z s / h = 0.04 and 0.49 and also a source of buoyant material with a dimensionless buoyancy parameter F ∗ = 0.024 and with release heights of z g/ h = 0.16 and 0.49. The buoyant line source is constructed by increasing, at t = 0, the temperature within the source with respect to the mean ambient temperature. When we interpret our instantaneous line-source results in terms of a continuous point source, we may compare our data with the well-established laboratory results of Willis and Deardorff ( Q. Jl R. Met. Soc. 102, 427–445, 1976a; Atmospheric Environment 15, 109–117,1981; 17, 2933-2447, 1983). The agreement with these experimental data is good for the case of the passive source but not as clear for the buoyant source. In the latter case the effects of plume rise are clearly noticeable in our calculation results but they do not seem to obey the standard plume-rise equations.