distribution of monocyclic aromatic hydrocarbons in ambient air of gas pump stations and hamadan city

background: the incomplete burning of fuel in engine of vehicles, evaporation of petrol from gas stations, and also car carburetor cause unburned hydrocarbons to be emitted in ambient air of cities and gas station locations. from unburned hydrocarbons; monocyclic aromatic hydrocarbon influence to citizen's health and benzene is known as carcinogenic compounds. the objectives of this study are to evaluate the distribution benzene, toluene, para-, orto- and meta-xylenes in ambient air of gas station locations and ambient air of hamadan county, iran. methods: for this purpose, a size of 50 samples was obtained with charcoal tube and personal pump sampling. samples were analyzed with gas chromatography equipped with flame ionizing detector. results: the results of data analysis were showed a significant difference between mean concentration of monocyclic aromatic in gas station locations and ambient air of hamadan city (p = 0.005) and the mean concentration of monocyclic aromatic hydrocarbons in ambient air in spring and summer was more than autumn and winter (p = 0.005). conclusion: low fuel prices and old motor technology, imply very large exhaust gas and particulate emissions. other ancillary factors are cited as well, including the relative shortage of modes of public transport, the relatively advanced age of cars and the consequent inefficiencies of their motors.