Dispersion modeling of particulate matter from ground-level area sources
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abstract
The new National Ambient Air Quality Standards (NAAQS) for particulate matter less than 2.5 m in diameter (PM2.5) and ozone will increase the number of nonattainment areas in the United States. Since a facility is responsible for all PM emissions originating from that property, an increased emphasis will be placed on the regulation of fugitive PM sources, as well. Dispersion modeling is often used by State Air Pollution Regulatory Agencies (SAPRA's) in determining whether the contribution of particulate matter from a facility meets the NAAQS. As such, a facility may be granted or denied an operating permit based on the results obtained from a dispersion model. However, the model currently approved by EPA over-predicts downwind concentrations of PM by as much as ten fold. This results in the possibility that a facility is denied a permit when, in fact, its emissions are well within the NAAQS. Dispersion models that provide accurate estimations of downwind concentrations of pollutant from these fugitive sources are needed to ensure reliable and fair regulation of pollutant sources. The presently accepted Gaussian-based models use dispersion profiles that do not accurately describe dispersion of pollutants from ground-level sources and inaccurately apply time averages to calculated concentrations. A new model, the Fritz-Meister Model, is being developed that contains a dispersion profile in the vertical plane that more accurately reflects dispersion from ground-level releases. The new model also applies a new area integration algorithm and uses a shorter time increment to allow for variation in wind direction and velocity. The result is a model that more accurately predicts concentrations downwind of ground-level sources and gives the modeler a greater degree of flexibility when modeling different pollutant types.
