Seyed Alireza Mostafavi - Department of Mechanical engineering, Faculty of engineering Arak University, Arak, Iran
Ali Karim - Department of Mechanical engineering, Faculty of engineering Arak University, Arak, Iran
Hamed Safikhani - Department of Mechanical engineering, Faculty of engineering Arak University, Arak, Iran

Arak city is considered as one of the most polluted cities in Iran due to the presence of various polluting industries, including refinery, petrochemical and power plant. These pollutants have devastating effects on humans and its reduction is especially important.In this paper, the effect of pollutant Nox released by these industries on Arak city has been analyzed and also the extent of this pollution.The modeling has been done in ermod software which is the state-of-the-science, steady-state Gaussian air dispersion model that is approved by United States Environmental Protection Agency for most refined modeling scenarios. A steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure and scaling concepts, including treatment of both surface and elevated sources, and both simple and complex terrain.Finally, according to the results, the amount of this pollutant only affected the winter and autumn seasons on the city of Arak and in other seasons it has a little impact on the city.