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Dispersion Modeling

Definition Overview

Definition

Dispersion modeling is a mathematical simulation of emissions as they are transported throughout the atmosphere.

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AQ System Flow Chart Highlighting AQ Modeling
Overview

Dispersion models replicate atmospheric conditions, (which includes wind speed and direction, air temperature and mixing height), and provide an estimate of the concentration of pollutants as they travel away from an emission source. These models can also generate estimates of secondary formation of pollution by incorporating atmospheric chemistry into the model. Dispersion models can be used to determine whether a new source will adversely impact an area or to predict whether the control of an individual source will have a beneficial effect. Dispersion models are used when a prediction of ambient concentrations is necessary, such as in a new source review or evaluating emissions reduction plans.

The available dispersion models vary in their complexity. At a minimum, most of the models require meteorological data, emissions data, and details about the facilities in question (such as stack height, gas exit velocity, etc). Some of the more complex models require topography information, individual chemical characteristics and land use data. The output from this type of model is a prediction of the concentration of the pollutant in question throughout the appropriate region (which depends on the model chosen).

EPA has detailed recommendations (PDF, 352 KB) regarding which models to use under what circumstances. Briefly, the recommended models include BLP, CALINE3, CALPUFF, CTDMPLUS, ISC3, and OCD. All of these models (and many more) are available for download on the EPA website.

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