The Dispersion Parameters
Point Source Dispersion Parameters:
Equations that approximately fit the Pasquill-Gifford curves are used to calculate sigy and sigz (in meters) for the rural mode. The equations used to calculate sigy are of the form:
sigy=465.11628 x tan (TH) (29)
TH=0.017453293[c - d ln(x)] (30)
In both Equations the downwind distance x is in kilometers. The equation used to calculate sigz is of the form:
where the downwind distance x is in kilometers and sigz is in meters.
Procedures Used to Account for Buoyancy-Induced Dispersion
The method of Pasquill is used to account for the initial dispersion of plumes. With this method, the effective vertical dispersion sze is calculated as follows:
sigze=[sigz2 +(Dh/3.5)]1/2 (32)
where sigz is the vertical dispersion due to ambient turbulence and Dh is the plume rise due to momentum or buoyancy. The lateral plume spread is:
sigye=[sigy2 +(Dh/3.5)]1/2 (33)
where sigy is the lateral dispersion due to ambient turbulence. It should be noted that Dh is the distance-dependent plume rise if the receptor is located between the source and the distance to final rise, and final plume rise if the receptor is located beyond the distance to final rise.
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.