Evaluation of Flat Versus Complex Terrain Models in Estimating Pollutant Transport and Deposition in Complex Terrain

Abstract

Estimation of potential human health risks associated with pollutants emitted into the atmosphere from the stacks of municipal waste combustors (MWCs), fossil fuel plants, and similar point sources requires accurate knowledge of annual average atmospheric pollutant concentrations and deposition rates in the areas surrounding these facilities. Values for these quantities are most often estimated through the use of atmospheric dispersion models. While a vast number of these models exist and are readily available for use, the risk assessor is generally faced with obstacles such as little or no data on the size and distribution of emitted particles, limited computing capability, crude meteorological measurements, or insufficient knowledge of terrain for the location being modeled. Consequently, common practice when determining exposure to pollutants emitted from these facilities has been to use air dispersion models which require minimal computing power and site specific information. The majority of these models are based on the Gaussian plume formulation and contain only limited provisions for dealing with complicated atmospheric processes such as pollutant deposition and flow in complex terrain (i.e. terrain exceeding the height of the stack). Of these, undoubtedly the most widely used are the U.S. Environmental Protection Agency (EPA) recommended Industrial Source Complex Short Term (ISCST) and Long Term (ISCLT) models (U.S. EPA, 1979).