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2.2 NON-POINT SOURCE EMISSIONS

2.2.1 General

As explained in Section 1.2.1, the ISC volume, area and open pit sources are used to simulate the effects of emissions from a wide variety of industrial sources.  Section 1.2.2 provides a description of the volume source model, Section 1.2.3 provides a description of the area source model, and Section 1.2.4 provides a description of the open pit model.  The following subsections give the volume, area and open pit source equations used by the long‑term model.

2.2.2 The Long‑Term Volume Source Model

The ISC Long Term Model uses a virtual point source algorithm to model the effects of volume sources.  Therefore, Equation (2‑1) is also used to calculate seasonal average ground‑level concentrations for volume source emissions.  The user must assign initial lateral (σyo) and vertical (σzo) dimensions and the effective emission height he.  A discussion of the application of the volume source model is given in Section 1.2.2.

2.2.3 The Long‑Term Area Source Model

The ISC Long Term Area Source Model is based on the numerical integration algorithm for modeling area sources used by the ISC Short Term model, which is described in detail in Section 1.2.3.  For each combination of wind speed class, stability category and wind direction sector in the STAR meteorological frequency summary, the ISC Long Term model calculates a sector average concentration by integrating the results from the ISC Short Term area source algorithm across the sector.  A trapezoidal integration is used, as follows:

where:

χi=    the sector average concentration value for the ith sector

 S =    the sector width
 fij =    the frequency of occurrence for the jth wind direction in the ith sector
 ε(θ) =    the error term - a criterion of ε(θ) < 2 percent is used to check for convergence of the sector average calculation
 χ(θij) =    the concentration value, based on the numerical integration algorithm using Equation (1-58) for the jth wind direction in the ith sector
 θij =    the jth wind direction in the ith sector, j = 1 and N correspond to the two boundaries of the sector.

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