Environmental and health risks of VOCs in the longest inner-city tunnel in Xi & rsquo;an, Northwest China: Implication of impact from new energy vehicles

Traffic source-dominated volatile organic compound (VOC) samples were collected during four time-intervals in a day (I: 7:30-10:30, II: 11:00-14:0 0, III: 16:30-19:30, and IV: 20:00-23:0 0) in a tunnel in summer, 2019, in Xi & rsquo;an, China. The total measured VOC (TVOC) in periods I and III (rush hours, 107.2 +/- 8.2 parts per billion by volume [ppbv]) was 1.8 times that in periods II and IV (non-rush hours, 58.6 +/- 13.8 ppbv), consistent with the variation in vehicle numbers in the tunnel. The considerably elevated ethane and ethylbenzene levels could have been attributed to emissions from compressed natural gas vehicles and the rapid development of methanol-fueled taxis in Xi & rsquo;an in 2019. The mixing ratios of benzene, toluene, ethylbenzene, and xylenes (BTEX) contributed 9.4%-12.7% to TVOCs, and the contributions were nearly 40% higher in periods I and III than in II and IV, indicating that BTEX levels were strongly affected by vehicle emissions. The indicators of motor vehicle emission, namely ethylene, propylene, toluene, m/p-xylenes, o-xylene, and propane, contributed to more than half of the ozone formation potential in this study. The noncarcinogenic risks of VOCs in this study were within the in-ternational safety standard, whereas the carcinogenic risks exceeded the standard by 2.3-4.6 times, suggesting that carcinogenic risks were more serious than noncarcinogenic risks. VOCs presented 2.2 and 1.4 times noncarcinogenic and carcinogenic risks during rush hours than during non-rush hours, respectively. Notably, the carcinogenic risk in period IV was comparable with that in period III; however, the vehicle numbers and VOC mixing ratios were the lowest at night, which may have attributed to the increasing number and proportion of methanol M100-fueled vehicles in the tunnel. Therefore, VOCs emitted by new energy vehicles should also be seriously considered while evaluating fossil fuel vehicle emissions. (c) 2021 Elsevier Ltd. All rights reserved