DETERMINATION OF BENZENE, TOLUENE AND XYLENE IN AMBIENT AIR OF CALCUTTA FOR 3 YEARS DURING WINTER

Calcutta is known to have serious air pollution problems. Benzene, tol uene and xylene (BTX) in the ambient air were monitored during the win ter 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 location s in Calcutta. Concentrations were found to be much higher than that f ound in similar studies performed elsewhere. The average benzene conce ntrations during the winter in 1992, 1993 and 1994 were 1004 mu g m(-3 ), 7082 mu g m(-3) and 491 mu g m(-3) respectively. The average compos itional 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 respectivel y. 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 variati on has been determined to be the result of variation in atmospheric pe rsistence of the released compounds due to thermal inversion. It is es timated that 5280 coal burning stoves per square kilometre are used fo r cooking in Calcutta. The median concentration of benzene, toluene an d xylene in the smoke plume above the coal burning stove used for cook ing, was found to be 5497 mu g m(-3), 4080 mu g m(-3), and 962 mu g m( -3) respectively. The compositional ratio of B:T:X for the coal burnin g cooking stoves was therefore 1:0.74:0.18. Automobile exhausts from d ifferent types of vehicles were also analysed for BTX. This study sugg ests that the primary sources of this high concentration of benzene ar e automobile exhaust and large number of coal burning stoves.