Turbulent diffusion in complex terrain.

Abstract

This review concentrates on aspects of air flow in complex terrains cocerning worst-case ground level air quality assessment, and phenomena important to pollution transport over scales of order several kilometers are stressed. A brief review is first given of some basic concepts in estimating pollutant concentrations. General considerations of mass conservation and thermodynamics are presented for streamline flow. Flow separation effects and the effects of stable stratification on the flow over objects are explained, and effects of clear air turbulence are discussed. Mathematical models for air craft and pollutant dispersion are discussed these being: potential flow theory (extended to include diffusion); stratified fluid theory; and modified potential flow models, dealing with channeling effects. Simple models for the prediction of ground level concentration ('NOAA', 'EPA' and 'ERT' Point Source Diffusion Model) are presented, though the author states that no well-accepted methodology exists. Details are given of some field measurement programmes on pollutant dispersion, and it is concluded that the rates of distribution of plumes in complex terrains are larger than those over level terrain. (I.F.)