Downwind and Crosswind Distances
The model uses a Cartesian receptor network. All receptor points are converted to Cartesian (X,Y) coordinates prior to performing the dispersion calculations. In the Cartesian coordinate system, the X axis is positive to the east of the user-specified origin and the Y axis is positive to the north. The user must define the location of each source with respect to the origin of the grid using Cartesian coordinates. If the X and Y coordinates of the source are X(S) and Y(S), the downwind distance x to the receptor, along the direction of plume travel, is given by:
where WD is the direction from which the wind is blowing. The downwind distance is used in calculating the distance-dependent plume rise and the dispersion parameters. The crosswind distance y to the receptor from the plume centerline is given by:
Wind Speed Profile
The wind power law is used to adjust the observed wind speed, uref, from a reference measurement height, zref, to the stack or release height, hs. The stack height wind speed, us, is used in the Gaussian plume equation. The power law equation is of the form:
where p is the wind profile exponent. Values of p may be provided by the user as a function of stability category and wind speed class. Default values are as follows:
The stack height wind speed, us, is not allowed to be less than 1.0 m/s.
Air pollution map (XY-Plane) produced by continuous discharge in time (three stacks). The red colour represents high pollutant concentrations. Wind: SE (135 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: E (90 dregrees) and 70 degrees.