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DFE World: Design & the Global Environment
Photograph of Nature
Air Pollution

Effective Stack Height

Mixing Height & Inversions

Model Output

Sensitivity Analysis



Central Campus Air Quality Model (CCAQM) Instructions


Point Sources

Point source models are a way to represent a steady stream of pollutants being ejected from a smokestack.  The point source model used in this tutorial is a Gaussian distribution, which is a statistical representation of the dispersion of emissions from the stack in a given space. 



Model Inputs

The Gaussian distribution of a point source is given by the following equation




  • C(x,y) = concentration at ground level at point (x,y) in units mg/m3

  • x = distance directly downwind, km

  • y = horizontal distance from the plume centerline, m

  • Q = emission rate of pollutants, mg/s

  • uH = average windspeed at effective stack height, m/s

  • H = effective stack height, m

  • σy = horizontal dispersion coefficient, a standard deviation, m

  • σz = vertical dispersion coefficient, m

Similarly to the line source model, horizontal and vertical dispersion coefficients are calculated in the following way:


σy(x) = ax0.894

σz(x) = cxd + f 


Note: x is distanced described in km, however, the solutions to σz(x) & σy(x) solve in terms of meters so no conversion needs to take place to input into the Gaussian equation above.


Parameters for calculating dispersion coefficients