Figure Showing Rotating Coordinates x and y With Respect to Fixed Coordinates X and Y
This coordinate system rotates with the wind direction. The direction of pollutant emission or pollutant plume will entirely depend on wind direction. Therefore lower case x is the distance downwind and along the direction of plume travel (the plume's centerline) from the downwind edge of the source to a point where the concentration is to be calculated. And lower case y is the cross wind direction from the plume centerline to a point where the concentration is to be calculated. As described in the figure. The point where the concentration is to be calculated is called a receptor. The ISC2 Model centers a grid or mesh of receptors about the user specified origin, that is the fixed axis, upper case X and Y. Notice that when modeling emissions from several area sources each area source will have its own rotating coordinate system. Further notice that the origin of these rotating coordinate systems will vary due to a 180 degree flip in wind direction. Fortunately, we can simplify things by relating the fixed coordinatate system to the rotating coordinate system; as indicated by the figure.
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