Source: U.S. Environmental Protection Agency (EPA), 1987, Industrial source complex (ISC) dispersion model user's guide—Second edition (Revised), Vol. 1, EPA-450/4-88-002a (Research Triangle Park, N.C.: Office of Air Quality Planning and Standards [December]).

Source: U.S. Environmental Protection Agency (EPA), 1987, Industrial source complex (ISC) dispersion model user's guide—Second edition (Revised), Vol. 1, EPA-450/4-88-002a (Research Triangle Park, N.C.: Office of Air Quality Planning and Standards [December]).

sion models, but it is not as straightforward as Holland's approach. For the Briggs equation, determining the buoyancy flux, Fb, is usually necessary using the following equation:

where:

g = the gravitational constant (9.8 m/s2) vs = the stack gas exit velocity, m/s ds = the diameter of the stack, m Ts = the stack gas temperature, deg. K AT = the difference between Ts and Ta (the ambient temperature), deg. K

When the ambient temperature is less than the exhaust gas temperature, it must be determined whether momentum or buoyancy dominates. Briggs determines a crossover temperature difference (AT)c for Fb > 55, and one for Fb < 55. If AT exceeds (AT)c, then a buoyant plume rise algorithm is used; if less, then a momentum plume rise equation is employed. The actual algorithms developed by Briggs to calculate the plume rise further depend upon other factors, such as the atmospheric stability, whether the plume has reached the distance to its final rise (i.e., gradual rise), and building downwash effects (U.S. EPA 1992d).

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