Type Of Release

Four types of releases can be simulated: point, area, line, and volume sources. Some models can be limited to the types of releases they handle. For most applications, line sources can be treated as area or volume sources, as well as in individual line models (see the subsection on mobile and line source modeling). Point sources are the most common modeling application and are defined by height, temperature, diameter, and velocity parameters.

In some cases, small or insignificant point sources may be grouped into either point or area sources to simplify the calculation. Area sources are only defined by a release height and the length of a side (which represents a square area). Models calculate the emissions from area sources using a virtual point source located some distance upwind so that the plume dispersion is equal to the width of the box at the center of the area source (see Figure 5.8.16). The models typically ignore concentrations calculated upwind and over the area source.

Volume sources represent continuous releases over a length, such as a conveyor or monitor. They are defined in the models by a release height, length of a side, and initial dispersions in the y and z directions (oy and oz). Simulation of these sources is similar to the virtual point source used for area sources.

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