Variation in the concentration of ground level ozone at selected sites in Delhi

To improve the quality of air in a city like Delhi which is mainly affected by vehicular exhaust, from 2002 onwards, CNG has been introduced, which shows remarkable change in the concentration of pollutants, but even then there are some pollutants like NOx, 0 3 which are still either crossing their permissible limits or at the margin of their crossing. Objective of the present study is to compare the variation in concentration of ground level ozone at three selected sites in Delhi which are distinct in vegetation and traffic densities and to monitor, if the prevailing meteorological conditions are responsible for spatial variation of pollution in Delhi. For this, the sampling was carried out during two seasons i.e. monsoon (Aug.Sept.’06) and winter season (Nov.-Dec.’06) at three sites -Site I (Inter State Bus Terminus ISBT), a high density traffic intersection area with low vegetation, Site II (Yamuna Biodiversity Park -YBP, Wazirabad), away from traffic intersection with high vegetation, and Site III (University of Delhi -DU, North Campus), an institutional area which is near to traffic intersection i.e. with moderate traffic density and high vegetation. The overall result shows that highest concentration of ground level ozone was found at Site II (YBP) followed by Site III (DU) and Site I (ISBT) in the month of monsoon (Sept’06) whereas interestingly, in the month of winter (Nov’06), the highest ozone concentration was found at Site III followed by Site II and then Site 1. This is might be due to the reason, at Site II in the month of September due to favourable meteorological conditions like less relative humidity which is negatively and highly significant to ozone concentration whereas, at Site III, in the month of November, this site is highly dense in vegetation and also near to traffic intersection so might be acting as an accumulation ozone of pollutants and moreover, with favourable meteorological conditions like increase in temperature which is positively correlated and highly significant with ozone concentration along with less relative humidity and wind speed which are negatively correlated with ozone concentration. Therefore, it was concluded that the site which is highly dense in vegetation and also have impact of vehicular emission exhibits high ozone concentration level than less vegetative area.