Modeling Tools for Environmental Engineers and Scientists

In the example shown, a three-dimensional contour plot with 10 contoursis chosen, and the other three options are commented out by the percent (%)sign. In line 33, the hold on command tells MATLAB ® to keep the settingsthe same for all the calculations specified under the for statement. To run thiscode, the user has to type in the call specifying the name of the M-File withthe arguments for MATLAB ® to execute the code in that file. The resultingplots in Figure 9.30 show the spatial distribution of the pollutant at the groundlevel at various times, as the puff is carried away by the wind.This example illustrates some of the mechanics involved in runninga MATLAB ® code interactively. However, for users not familiar with theMATLAB ® environment, this may not be intuitive and easy to adapt. Forexample, accessing the M-File or modifying it to pick the desired type of plot,or changing the grid sizes, etc., requires some familiarity with the MATLAB ®environment. MATLAB ® includes tools to create a user-friendly GUI throughwhich a novice can intuitively run MATLAB ® files interactively, by clickingbuttons and entering inputs through dialog boxes. Such an interface will beincluded in the next example, where the plume model is illustrated.9.11 MODELING EXAMPLE: AIRPOLLUTION—PLUME MODELIn this example, the computer implementation of the plume model to predictspatial concentrations resulting from a continuous source of air pollutantis illustrated. Again, the well-known Gaussian Dispersion Model and its solutionproposed by Pasquill and Gifford are used here. The objective is todevelop a model incorporating a user-friendly interface for novices to run themodel under various scenarios and generate plots to aid in visual appreciationand analysis of the problem.The following equations describe the steady state, spatial distribution,and ground-level concentrations of nonreactive gaseous or aerosol (diameter< 20 µm) pollutants emitted by a stack of effective height, H:Spatial distribution:MC(x,y,z) = 2πσ yσ z U exp – 2yGround-level distribution (z = 0):2σ2 – (z – H22σyC(x,y,z) = πσMz) 2 exp – 2yyσ z U + exp – 2y2Hσ2 – 2 σy22 z2σ2 – (z + Hz2σy) 22where M is the mass rate of emission, U is the mean wind velocity in the x directionand σ y and σ z are the horizontal and vertical dispersion coefficients.© 2002 by CRC Press LLC