Evaluation of a Dispersion Modeling Software Package (Case Study: Traffic Pollutants in Shiraz Iran)

The AERMOD is one of the EPA preferred and recommended air quality dispersion models. The AERMOD is a steady state dispersion model for estimating the concentration of pollutants in urban, rural, flat and elevated, ground level and elevated receptors from different volumes, areas or point sources. In this study, in order to evaluate the accuracy of software results, the AERMOD was used for estimating the air pollution concentrations at different locations in Emam Hossein Square and Darvazeh Kazeroun Square of Shiraz City, where there are two DOE air quality monitoring stations. The modeling was performed based on hourly annual metrological data of Shiraz airport. The variable air pollutants’ emission rates were used based on different traffic loads at different hours at night and during the day. The modeling results are compared with the values measured at DOE air quality monitoring stations. The results showed that for the maximum daily concentration of pollutants, the AERMOD estimated values were about 5 and 20 percent higher than the values measured for SO2 and CO; also, the estimated values were two times higher than the measured values for NOx and PM10. Furthermore for the average daily concentration of pollutants, the AERMOD estimated values were about 17, 41, 42 and 38 percent lower than the values measured for NOx, CO, SO2 and PM10, respectively. The quality of ambient air in Shiraz City seems to be good since, except for the PM10, the concentrations of CO, NOx and SO2 were in the range of clean air standard. The maximum daily concentrations of PM10, CO, NOx and SO2 were reported as 0.497 mg/m3, 4246 mg/m3, 0.206 mg/m3and 0.037 mg/m3, respectively.