Spatial and temporal variability of VOCs and its source estimation during rush/non-rush hours in ambient air of Delhi, India

The present study deals with the concentrations of individual and total volatile organic compounds (TVOCs) present in the ambient atmosphere of Delhi. Sampling was done in four different zones, viz. residential, commercial, industrial and heavy traffic density area (HTDA) during rush and non-rush hours. The National Institute for Occupational Safety and Health (NIOSH)-1501 standard method was used for benzene, toluene, ethylbenzene and xylene (BTEX) measurements while real-time monitoring was done for TVOC using a data-logging photoionization detector. Results showed that the mean concentrations of TVOC and ∑BTEX were found to be highest in HTDA as compared to those in other zones. Toluene contributed the most among BTEX as 28.5, 108.6, 129.6 and 104.5 μg/m3 at residential, commercial, industrial and HTDA, respectively. However, the concentrations of TVOC were found to be 518.9 μg/m3 in HTDA followed by industrial (511.3 μg/m3), commercial (429.6 μg/m3) and residential areas (199.5 μg/m3). It is noted that the concentrations of the pollutants were observed to be higher during rush hours in contrast to non-rush hours due to more number of vehicles plying the road. After examining the seasonal variability, the winter samples showed the highest concentrations of the pollutants which could be due to stable environment. In order to identify the sources, characteristic ratios and correlation analysis were also done. Cancer and non-cancer risks were estimated for BTEX using US Environmental Protection Agency (USEPA) guidelines. The estimated lifetime cancer risk (LCR) in this study exceeded the value of 1.0 × 10−6 recommended by the USEPA for adults and children in all zones. The population groups are in the category of “possible risk” after comparing with the Sexton’s classifications of cancer risk.