8.4 LIMITATIONS

        The complex terrain components use approximations based on average conditions to improve the accuracy of simulation of environmental conditions. Although the components described above will provide a reasonable estimate of the average exposures, these components involve gross simplifications of the atmospheric processes. Case studies of air movements in complex terrain demonstrate the need for much more sophisticated models to predict detailed exposure patterns. The MEPAS atmospheric component is only designed to provide order-of-magnitude estimates of exposures in complex terrain.

        The computation of the maximum individual exposure generally will be more sensitive to the effects of complex terrain than the population exposure. However, in situations where the tendency for air to flow (or not to flow) from the release to surrounding population centers is controlled by terrain effects, the complex terrain features can significantly affect population exposures.