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DFE World: Design & the Global Environment
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Air Pollution

Atmospheric Stability

Dispersion Coefficients

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Central Campus Air Quality Model (CCAQM) Instructions


Horizontal and Vertical Dispersion Coefficients

Dispersion varies from being fastest for very unstable conditions to being slowest for very stable conditions.  Dispersion coefficients are the standard deviations of the horizontal (σy) and vertical (σz) normal distributions in units of meters.  Empirical approximations have been developed to calculate σy(x) and σz(x), where x is the distance downwind from the source in units of kilometers.  These coefficients can be computed using the following information:

σy(x) = ax0.894

σz(x) = cxd + f

Parameters for calculating dispersion coefficients