How do Tehran’s surrounding mountains trap polluted air?

Tehran’s geographical location significantly contributes to its persistent air pollution challenges. The city is surrounded by mountains that act as a physical barrier, preventing the dispersal of pollutants generated by motor vehicles, household fuel, and industrial activity.12

This entrapment is exacerbated by specific atmospheric conditions. For approximately two-thirds of the year, pollutants from fossil fuels become locked beneath a dome of hot air. Because the north winds lack the strength to clear this stagnant air, the city remains unable to effectively dissipate its atmospheric waste. Furthermore, the prevailing winds from the west, south, and southeast often transport additional pollutants from industrial areas into the city, compounding the issue. These factors, combined with limited annual precipitation, prevent the natural cleansing of the atmosphere.1