AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

6.6 Source Characterization

AERMOD gives the user the ability to characterize a source as either a point, an area, or a volume. AERMOD additionally has the capability of characterizing irregularly shaped area sources.

Point sources are characterized exactly as in the ISC3 model (USEPA, 1995). The input to the model includes the location, elevation, emission rate, stack height, stack gas temperature, stack gas exit velocity, and stack inside diameter. The temperature, exit velocity, and diameter are required for plume rise calculations.

Similarly, volume sources require the same input as the ISC3 model. This includes the location, elevation height (optional), height of release, emission rate, the initial lateral plume size (y ) and y initial vertical plume size (z ). AERMOD differs from ISC3 in the treatment of volume sources z only in how the initial plume size is implemented. Where ISC3 uses the virtual source technique to account for initial plume size, AERMOD adds the square of the initial plume size to the squareof the ambient plume size:

Equation (128)

The area source treatment is enhanced from that available in ISC3. In addition to being input as squares or rectangles, area sources may be input as circles or polygons. A polygon may be defined by up to 20 vertices. A circle is defined by inputting its center location and radius. The AERMOD code uses this information to create an equivalent nearly-circular polygon of 20 sides, with the same area as the circle.

As with ISC3, AERMOD allows for the calculation of a simple half-life decay.