The Decay Term (D)
The Decay Term is a simple method of accounting for pollutant removal by physical or chemical processes. It is of the form:
D=exp(-psi x/us) for psi > 0 (36)
D=0 for psi = 0 (37)
psi= the decay coefficient (s-1) (a value of zero means decay is not considered)
x= downwind distance (m)
For example, if T1/2 is the pollutant half life in seconds, the user can obtain y from the relationship:
The default value for psi is zero. That is, decay is not considered in the model calculations unless y is specified. However, a decay half life of 4 hours (y = 0.0000481 s-1) corresponds to SO2 when modeled.
Air pollution map (XY-Plane) produced by continuous discharge in time (three stacks). The red colour represents high pollutant concentrations. Wind: W (270 degrees).
Air pollution map (XY-Plane) produced by continuous discharge in time. The fucshia lines represents a stacks in the XY-Plane. The red colour represents high pollutant concentrations. Winds: NE (45 dregrees) and 145 degrees.