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/m3,
0.361 μg/m3, 1.037 μg/m3 and
0.122 μg/m3. The average concentration of benzene was
highest at petrol pump 3.5 μg/m3 however at all other sampling sites it was in
the range of 0.294 to 0.712 μg/m3. 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.