Razi University

In recent years, the increasing emission of gaseous pollutants from industrial activities and combustion sources has emerged as a major environmental challenge. Among these pollutants, nitrogen dioxide (NO?) is of particular concern due to its adverse effects on human health and ambient air quality. The aim of this study is to investigate the dispersion behavior of NO? under different flow conditions and environmental parameters using Computational Fluid Dynamics (CFD) simulations. In this study, the effects of inlet wind velocity within the atmospheric boundary layer in the range of 1.5–5 m/s, flue gas outlet temperature in the range of 416–716 K, ambient temperature in the range of 259–323 K, and relative humidity ranging from 0 to 90% were investigated as key parameters influencing pollutant dispersion. The results obtained from velocity contours and NO? mass fraction distributions demonstrated that increasing the flow intensity enhances momentum transfer and promotes mixing of the pollutant with the surrounding air, thereby altering its dispersion pattern. By varying the aforementioned parameters, the maximum NO? mass fraction was evaluated at a distance of 100 m from the last stack. The results showed that increasing the ambient temperature from 0 to +50 °C increased the maximum NO? mass fraction from 0.00030 to 0.00035, corresponding to a 17% increase. Furthermore, increasing the stack outlet temperature from 416 to 716 K resulted in an increase in the maximum NO? mass fraction from 0.00025 to 0.00040, corresponding to a 60% increase. In contrast, increasing the wind velocity from 1.5 to 5 m/s reduced the maximum NO? mass fraction from 0.00025 to 0.00005, corresponding to an 80% decrease, and exhibited the most pronounced effect on pollutant dispersion. The simulation results also indicated that variation in relative humidity over the range of 0–90% had a relatively minor effect on NO? dispersion, with a maximum influence of approximately 5%. Overall, the CFD simulation predictions revealed that wind velocity is the primary controlling factor governing NO? dispersion, while stack outlet temperature has a significant effect, ambient temperature exerts a moderate influence, and relative humidity has the least effect on the intensity of NO? dispersion.