Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an, 710049, China; SKLLQG, Key Lab of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710061, China.
Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
Environ Pollut. 2021 Aug 1;282:117057. doi: 10.1016/j.envpol.2021.117057. Epub 2021 Apr 1.
Traffic source-dominated volatile organic compound (VOC) samples were collected during four time-intervals in a day (Ⅰ: 7:30-10:30, Ⅱ: 11:00-14:00, Ⅲ: 16:30-19:30, and Ⅳ: 20:00-23:00) in a tunnel in summer, 2019, in Xi'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'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 international 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.
2019 年夏季，在中国西安的一条隧道内，在一天中的四个时间间隔（Ⅰ：7:30-10:30，Ⅱ：11:00-14:00，Ⅲ：16:30-19:30 和 Ⅳ：20:00-23:00）采集了交通源主导的挥发性有机化合物（VOC）样品。Ⅰ期和Ⅲ期（高峰时段，体积浓度 107.2±8.2 十亿分率 [ppbv]）的总测量 VOC（TVOC）是Ⅱ期和Ⅳ期（非高峰时段，58.6±13.8 ppbv）的 1.8 倍，这与隧道内车辆数量的变化一致。乙烷和乙苯水平的显著升高可能归因于压缩天然气车辆的排放以及 2019 年西安甲醇燃料出租车的快速发展。苯、甲苯、乙苯和二甲苯（BTEX）的混合比占 TVOCs 的 9.4%-12.7%，Ⅰ期和Ⅲ期的贡献比Ⅱ期和Ⅳ期高近 40%，表明 BTEX 水平受到车辆排放的强烈影响。机动车排放指标，即乙烯、丙烯、甲苯、间/对二甲苯、邻二甲苯和丙烷，对本研究中的臭氧形成潜力贡献超过一半。本研究中 VOC 的非致癌风险处于国际安全标准范围内，而致癌风险超标 2.3-4.6 倍，表明致癌风险比非致癌风险更严重。与非高峰时段相比，高峰时段 VOC 的非致癌和致癌风险分别增加了 2.2 倍和 1.4 倍。值得注意的是，第Ⅳ期的致癌风险与第Ⅲ期相当；然而，夜间车辆数量和 VOC 混合比最低，这可能是由于隧道内甲醇 M100 燃料车辆的数量和比例增加所致。因此，在评估化石燃料车辆排放时，还应认真考虑新能源汽车排放的 VOC。
