1 Microscopic Aspects of Turbulent Transport –Atmospheric Dispersion of

Abstract: A turbulent scalar transport model is proposed which is based on the analytical framework provided by spectral theory of turbulence and penetration theory. The new phenomenological model unifies diffusion and convection terms in a single transport equation, incorporating molecular properties of the diffusing scalar. In describing the turbulent dispersion of gases in atmospheric turbulent boundary layer, a concept of two turbulent time scales is introduced. The dispersive time scale for horizontal dispersion in the atmosphere is taken to be the reciprocal of geostrophic frequency, a well known parameter in earth science. The dissipative time scales for various stability classes are determined using Pasquill-Gifford experimental correlation. Proposed model predicts horizontal dispersion coefficient under various stability conditions within ± 20 % of Random Force theory. Model is extended for vertical dispersion using bulk Richardson number which seems to perform reasonably well