Introduction: Air pollution, especially in the two pollutants of suspended particles less than 2.5 microns and sulfur dioxide, is one of the important problems of large and industrial cities of Iran, including in Tehran, especially in the cold half of the year, which affects the health and comfort of citizens.
Objectives: The severity and weakness of air pollution in Tehran is related to climatic patterns and the dominance of air masses over the city of Tehran.
Methodology: By following the air pollution during the year 2019, this research investigated the pollutant variables on a monthly, daily and hourly basis for 4 districts 2, 5, 9 and 18 of Tehran city in five pollution measurement stations and based on three climate scenarios: effect of stability, instability and inversion, separate clean and polluted days and investigate the role of air masses dominating the city for both conditions. To better understand the relationship between the weather patterns governing the study area, atmospheric conditions at 1000 and 500 millibar levels, as well as the earth's surface map, have been analyzed. Air pressure, temperature, rain and wind are the elements that have been investigated. Pollutant measurement data were obtained from stations located in the four districts of Tehran municipality and from the air quality control company affiliated to Tehran municipality, and meteorological data were obtained from the country's meteorological organization, and finally, radiosonde data from Mehrabad station were used for the inversion study.
Geographical Context: the area of study in this research is Tehran and its 4 municipal zones 2, 5, 9 and 18.
Result and Discussion: The research results show that the air quality of the study area has a strong dependence on the development of the geopotential ridge in the middle troposphere, the absence of wind blowing at a significant speed on the surface of the earth, the extreme stability of the air and the creation of a dynamic inversion layer or subsidence at high altitude. In other words, periods of air pollution intensity are related to weak pressure gradient, calm wind, air subsidence and temperature inversion.
Conclusion: Finally, during severe and critical pollution, high-pressure air dominates the city surface and the air is stable, and the wind either does not exist or is less than 3 meters per second, which does not have the power to purify the air. In the defined scenarios, the presence of strong wind (over 6 meters per second) is the best solution for having clean air, and rainfall is effective in removing pollution only when it rains heavily and for a long time.