Weather and climate have considerable influence on the concentration of air pollutants such as particles and gases. The range and concentration of these particles and gases are very dependent on prevailing weather conditions and air currents. This research concentrates on health effects of benzene, one of the air pollutants of Tehran, as a major city. The concentration of benzene emission to air due to deficient oxidation of fuel in vehicles or evaporation of gasoline at gas stations and the gas tanks of the automobiles, at market station in Tehran shows significantly high values than EPA guidelines that is used in Iran. The result of calculation of risk assessment was 3.6 Ã— 10-5 (3.6 cancers per 100000).