Derivation of an eddy diffusivity depending on source distance for vertically inhomogeneous turbulence in a convective boundary layer

Accounting for the current knowledge of the convective boundary layer struc ture and characteristics, a new formulation for the eddy diffusivities to b e used in atmospheric dispersion models has been derived. That is, expressi ons for the eddy diffusivities, depending on source distance, for inhomogen eous turbulence are proposed. The classical statistical diffusion theory, t he observed spectral properties, and observed characteristics of energy-con taining eddies are used to estimate these parameters. In addition, a vertic al eddy diffusivity was introduced into an air pollution model, validated w ith the data of Copenhagen experiments, and compared with an improved Gauss ian model. The results of this new method are shown to agree with the measu rements of Copenhagen and also with those of the Gaussian model. Furthermor e, the current study suggests that the inclusion of the memory effect, impo rtant in regions near an elevated continuous point source, improves the des cription of the turbulent transport process of atmospheric contaminants. Th e major advance shown in this paper is the necessity of including the downw ind distance-dependent eddy diffusivity in air quality modeling, and it is demonstrated that such theory would suggest that it should yield better res ults than the asymptotic solution alone. It, in fact, does yield better res ults in the near and intermediate fields.