1. Introduction
In many air pollution problems, it is essential to determine the concentration of
pollutants downwind from a continuous source. The use of Gaussian dispersion
algorithms require the estimation of horizontal and vertical growth of the plumes
for predicting the Ground Level Concentration (GLC). The horizontal and vertical
growth of plumes are generally expressed in terms of standard deviations of concentrations
in lateral (y) and vertical (z) directions, i.e., y and z respectively and
parmeterise the dispersion due to atmospheric turbulence. The values of standard
deviations grow with the diffusion time and their rates of growth depend mainly
on meteorological variables such as Richardson number and wind characteristics.
These relationships may be based on empirical results, or can be inferred from
Taylor’s diffusion theorem (Taylor, 1921). In summary the dispersion coefficients
could be parameterised and classified broadly in the following two categories: