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Tehran is one of the polluted cities of the world. Among the factors affecting this phenomenon the geographical location and characteristics of the city are very influential and important. The orientation of topography has blocked the city from north and east. The prevailing westerlies bring pollutants from factories to the west into the city. Travelling westerly anticyclones and frequent inversions during winter season retain the pollutants over the city. The physical setting of the city indicates that the managers and planners of the city should consider these constraints and manage the overcrowded population and miss-located factories. The best way is to expand the green space and to encourage the citizens to develop measures to lower the pollution producing activities and widen the green space.

Key words: Pollution, Tehran, Geographical factors and air pollution, Urban air pollution.