PREDICTION OF NO2 CONCENTRATIONS IN A GAS REFINERY USING AIR DISPERSION MODELING.

Nitrogen dioxide (NO₂) is considered as one of the most important ambient air pollutants in gas refineries. In this study, AERMOD dispersion model was applied for prediction of NO₂ ambient concentrations and dispersion patterns from point sources, including 13 stacks and six flares in a gas refinery located in Asaluyeh, Iran. For this purpose, the NO₂ concentrations exhausted from the stacks were measured by a portable emission analyzer and the NO₂ concentrations resulted from the flares were estimated using the emission factors. Moreover, the amounts of ambient NO₂ concentrations in 10 monitoring stations were measured in four seasons. Then, the ambient NO₂ concentrations and dispersion patterns were predicted using the AERMOD model within a domain of 10 × 10 km², in 1-hr and 12 months averages and the unhealthy zones in the study area were defined. The results revealed that for both annual observed and predicted values, ambient NO₂ concentrations were higher than WHO standard limits but they did not exceed the US EPA standard limits. However, the hourly observed and predicted concentrations were lower than the standard levels. Statistical methods were used for comparing the predicted and observed NO₂ concentrations. Simulation results indicated that the predicted concentrations were underestimated by a factor of 20% in comparison to the measured ones which revealed the estimated contribution of other sources including mobile sources and neighbor sources located in the vicinity of the gas refinery. [ABSTRACT FROM AUTHOR]