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

Where:

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
u_H = average windspeed at effective stack height, m/s
H = effective stack height, m
σ_y = horizontal dispersion coefficient, a standard deviation, m
σ_z = vertical dispersion coefficient, m

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

σ_y(x) = ax^0.894

σ_z(x) = cx^d + f

Note: x is distanced described in km, however, the solutions to σ_z(x) & σ_y(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