Distribution of volatile organic compounds in ambient air of Tehran

Transportation sources have created a major hydrocarbon pollution problem i n the ambient air of Tehran. The authors used a Carbotrap tube to determine volatile organic compounds in air. Such compounds can be desorbed thermall y and analyzed with gas chromatography-mass spectrometry. Samples were obta ined from 8 sites in Tehran at which traffic flow varied between 500 and 2, 500 vehicles/hr. A total of 54 hydrocarbons were identified in the ambient air of Tehran, and the average measured concentrations of benzene, toluene, m- and p-xylene, ethyl benzene, and o-xylene were 127.6 mug/m(3), 201.1 mu g/m(3), 110.7 mug/m(3), 58.1 mug/m(3), and 57.6 mug/m(3), respectively (sta ndard deviation = 3.8-51.7 mug/m(3)). Emissions of individual pollutants in south Tehran exceeded those in north Tehran, and these emissions were high er during the afternoon than during the morning. The geographical parameter s and the photochemical reaction also played important roles in the polluti on conditions.