RANDOM-WALK MODEL STUDIES OF THE TRANSPORT AND DIFFUSION OF POLLUTANTS IN KATABATIC FLOWS

The flow and turbulence quantities governing dispersion in katabatic f lows vary with both height and downslope distance. This variation cann ot be accounted for in conventional plume dispersion models. In this s tudy, three random-walk models of varying complexity are formulated to simulate dispersion in katabatic flows, and their strengths and weakn esses are discussed. The flow and turbulence parameters required by th ese models are determined from a high-resolution two-dimensional katab atic flow model based on a turbulent kinetic energy closure. Random-wa lk model calculations have been performed for several values of source height and slope angle to examine the influence of these parameters o n dispersion. Finally, we simulated the perfluorocarbon and heavy meth ane tracer releases for Night 4 of the 1980 ASCOT field study over a n early two-dimensional slope in Anderson Creek Valley, California. The observed peak concentrations are generally well-predicted. The effects of the pooling of the drainage air could not be taken into account in our katabatic flow model and, consequently, the predicted concentrati ons decay much more rapidly with time than the observed values.