Determination of Benzene, Toluene and Xylene in Ambient Air of Calcutta for Three Years During Winter

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Abstract
Calcutta is known to have serious air pollution problems. Benzene, toluene and xylene (BTX) in the ambient air were monitored during the winter from 1992 to 1994 inclusive. Activated carbon traps were used for sampling and a simple packed column gas chromatography methodology was used for analyses in this study. Samples were collected in 5 locations in Calcutta. Concentrations were found to be much higher than that found in similar studies performed elsewhere. The average benzene concentrations during the winter in 1992, 1993 and 1994 were 1004 µg m−3, 7082 µg m−3 and 491 µg m−3 respectively. The average compositional ratios of benzene:toluene:xylene (B:T:X) in winter were 1:0.39:0.05, 1:0.16:0.04 and 1:0.26:0.13 for 1992, 1993 and 1994 respectively. The toluene/benzene concentration ratio in the samples varied from 1.033 at the end of summer to 0.092 at the end of winter. This variation has been determined to be the result of variation in atmospheric persistence of the released compounds due to thermal inversion. It is estimated that 5280 coal burning stoves per square kilometre are used for cooking in Calcutta. The median concentration of benzene, toluene and xylene in the smoke plume above the coal burning stove used for cooking, was found to be 5497 µg m−3, 4080 µg m−3, and 962 µg m−3 respectively. The compositional ratio of B:T:X for the coal burning cooking stoves was therefore 1:0.74:0.18. Automobile exhausts from different types of vehicles were also analysed for BTX. This study suggests that the primary sources of this high concentration of benzene are automobile exhaust and large number of coal burning stoves.

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