It is a matter of concern that despite taking measures to control aromatic content in gasoline in India, the levels of volatile organic compounds are rising again in many of the Indian cities. The transport sector has been one of the major sectors which are responsible for worsening the air quality of Delhi city. While thousands of toxic compounds are emitted from automobiles, industries, gasoline stations as well as service stations, however, volatile organic compounds are important due to their significant contribution to ozone formation, cancer, and non-cancer health risks. In this study, roadside levels of benzene, toluene, ethylbenzene and xylenes (BTEX) were investigated at the one of the major arterial road of Delhi city. Air samples were collected by activated coconut shell charcoal adsorbent tubes. The BTEX concentrations were determined by gas chromatography-flame ionization detector (GC-FID) technique. The mean concentrations of benzene, toluene, ethylbenzene and xylenes were, respectively, 60.22, 162.68, 49.42 and 25.25 μg/m 3. The relative concentration distribution pattern and mutual correlation analysis indicated that in BTEX had sources other than vehicle emission at the study site. The samples collected, showed that BTEX had significantly higher concentrations in winter than those in spring and summer.

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ACKNOWLEDGEMENTS. The façade testing facility at IIT Gandhinagar was sponsored by the Underwriters Laboratories. Generous support from IIT Gandhinagar for providing land and for allocating financial resources to enable elaborate instrumentation of the building is acknowledged. We thank Mr Kumud Chandra Suthar (Ahmedabad) for help with the construction of this facility; support from M/s Shah Bhogilal Jethalal and Brothers (Ahmedabad) for providing the necessary fire protection systems.

The present study aims to provide an indication of ambient levels of BTEX in the immediate vicinity of petrol filling stations in Delhi & other road side corridors of Delhi. In this study spatial and seasonal variation of BTEX has been measured at different locations in Delhi. For the measurement of VOCs, passive based diffusion methodology was adopted for the adsorption of BTEX over the activated charcoal. Four categories of sampling sites were chosen (residential, traffic junctions, road side corridors and petrol pumps). The result confirms that the aromatic concentrations in the ambient air of gas stations are appreciably higher than the average values in locations with high vehicular flux. The mean concentration of BTEX at all the locations was 0.622μg/m 3 , 0.361 μg/m 3 , 1.037 μg/m 3 and 0.122 μg/m 3. The average concentration of benzene was highest at petrol pump 3.5 μg/m 3 however at all other sampling sites it was in the range of 0.294 to 0.712 μg/m 3. The mean concentration value shows that the xylene concentration dominates more in Delhi as compared to benzene. The total average BTEX concentration at road side corridors was 0.594 μg•m −3 , at residential corridors was 0.262 μg•m −3 , at intersections it was 0.649 μg•m −3 and at petrol filling stations it was 1.457 μg•m −3. The concentration was in the order of petrol filling stations > intersections > road side corridors > residence. These data show the predominance of diesel driven vehicles in Delhi since xylene mainly comes from diesel exhausts. The influential VOC species in case of diesel engine exhaust are benzene, ethylbenzene, xylenes, propane, n-decane and undecane and in case of gasoline vehicle exhaust influential species are benzene, ethylbenzene, 1,2,4-methylbenzene, 1,3,5-methylbenzene, n-hexane and 2-methylhexane. So xylene is mainly coming from diesel exhaust since gasoline vehicle exhaust doesn't show this species.