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One of the important prerequisites for a model to be used in decision making is to perform uncertainty and sensitivity analyses on the outputs of the model. This study presents a comprehensive review of the uncertainty and sensitivity analyses associated with prediction of ground level pollutant concentrations using the USEPA's AERMOD equations for point sources. This is done by first putting together an approximate set of equations that are used in the AERMOD model for the stable boundary layer (SBL) and convective boundary layer (CBL). Uncertainty and sensitivity analyses are then performed by incorporating the equations in Crystal Ball ® software. Various parameters considered for these analyses include emission rate, stack exit velocity, stack exit temperature, wind speed, lateral dispersion parameter, vertical dispersion parameter, weighting coefficients for both updraft and downdraft, total horizontal distribution function, cloud cover, ambient temperature, and surface roughness length. The convective mixing height is also considered for the CBL cases because it was specified. The corresponding probability distribution functions, depending on the measured or practical values are assigned to perform uncertainty and sensitivity analyses in both CBL and SBL cases. The results for uncertainty in predicting ground level concentrations at different downwind distances in CBL varied between 67% and 75%, while it ranged between 40% and 47% in SBL. The sensitivity analysis showed that vertical dispersion parameter and total horizontal distribution function have contributed to 82% and 15% variance in predicting concentrations in CBL. In SBL, vertical dispersion parameter and total horizontal distribution function have contributed about 10% and 75% to variance in predicting concentrations respectively. Wind speed has a negative contribution to variance and the other parameters had a negligent or zero contribution to variance. The study concludes that the calculations of vertical dispersion parameter for the CBL case and of horizontal distribution function for the SBL case should be improved to reduce the uncertainty in predicting ground level concentrations.

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