A comprehensive study on spatio-temporal distribution, health risk assessment and ozone formation potential of BTEX emissions in ambient air of Delhi, India Anchal Garg, N.C. Gupta ⁎ University School of Environment Management, Guru Gobind Singh Indraprastha University, Sector- 16 C, Dwarka, New Delhi 110078, India HIGHLIGHTS • Average BTEX level of all sampling sites was 46.66 μg/m 3 . • BTEX levels were found maximum at roadside site followed by connectivity hub site during morning rush-hours. • Cancer risks obtained as more than 1E- 06, showing significant long-term health effects. • Hazard quotient of non-cancer risks ob- tained b1, indicates no adverse effects of BTEX on human health. • The total ozone formation potential of BTEX was obtained as 207.51± 123.40 μg/m 3 . GRAPHICAL ABSTRACT abstract article info Article history: Received 28 October 2018 Received in revised form 27 December 2018 Accepted 28 December 2018 Available online 29 December 2018 Editor: Jianmin Chen The hazardous air pollutants like benzene, toluene, ethylbenzene and xylene (BTEX) are considered as toxic be- cause of their role in ozone formation and adverse effects on human health. Owing to this, the present study was carried out at six spatially distributed sites in Delhi from November 2017- June 2018. Activated charcoal tubes were used to collect samples of BTEX and were further analyzed using GC-FID. The minimum BTEX concentration was found at institutional site (9.94 μg/m 3 ) and maximum at roadside site (103.12 μg/m 3 ) with the average of 46.66 μg/m 3 . Also, the levels of BTEX were 1.18–1.74 times higher during rush hours as compared to non-rush hours. The high T/B ratio (2.26–3.41) observed is the indication of the traffic-originated sources of emission. The cancer risks calculated for benzene at probability 0.50 ranged as 1.29E-06 – 1.80E-05, whereas 4.09E-06 – 3.40E-05 at probability 0.95, which were higher than the acceptable value of 1.0E-06. The non-cancer health risks in terms of hazard index were observed less than unity i.e. within acceptable limit. The total ozone forma- tion potential (OFP) was obtained as 207.51 ± 123.40 μg/m 3 with maximum potential by toluene. Such high levels of BTEX, cancer risks and OFP obtained in the study especially at roadside and connectivity hub are harmful for people residing near these areas, and also to large commuters, who are exposed to such emissions during travelling. © 2018 Elsevier B.V. All rights reserved. Keywords: Ambient air BTEX Health risks Ozone formation potential Hazard quotient Cancer risk 1. Introduction The urban air quality of Delhi, the National Capital Territory (NCT) of India is getting deteriorate due to rapid increase in the number of motor Science of the Total Environment 659 (2019) 1090–1099 ⁎ Corresponding author. E-mail address: ncgupta.ip@gmail.com (N.C. Gupta). https://doi.org/10.1016/j.scitotenv.2018.12.426 0048-9697/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv