
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 crosswind 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 semiempirical solution of a set of partial differential equations.
