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Gaussian plume models

The model which is most frequently used as the basis for more complex air pollution calculations is the Gaussian plume model. This model assumes that over short periods of time, say one or a few hours, steady state conditions exists with regard to air pollutant emissions and meteorological changes. Conceptually, the model is symbolised by this figure. Air pollution is represented by an idealised plume coming from the top of a stack. Because the plume is being produced by a burning process, the hot plume will be thrust upward some distance above the top of the stack, to the effective stack height. The actual value of this vertical displacement will depend on the stack gas exit velocity and temperature, and the temperature of the surrounding air. Once the plume has reached effective stack height, dispersion will begin in three dimensions. Dispersion in the downwind direction will be proportional to the mean wind speed and in that direction. Dispersion in the cross-wind direction and in the vertical direction will be governed by the Gaussian plume equations. Model coefficients are related to, and distance from the source. The model assumes that dispersion in these two dimensions will take the form of a normal Gaussian curve, with the maximum concentration in the centre of the plume. The solution of the model involves a semi-empirical solution of a set of partial differential equations.

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