INESC TEC - INESC Technology and Science, University of Porto, Porto, Portugal.
FP-ENAS - UFP Energy, Environment and Health Research Unit, University Fernando Pessoa, Porto, Portugal; LAQV, REQUIMTE, University of Porto, Porto, Portugal; Faculty of Health Sciences, University Fernando Pessoa, Porto, Portugal.
Environ Pollut. 2019 Dec;255(Pt 1):113100. doi: 10.1016/j.envpol.2019.113100. Epub 2019 Aug 31.
Diesel-fueled buses have been replaced by Compressed Natural Gas (CNG) to minimize the high level of emissions in urban areas. However, differences in indoor exposure levels to Benzene, Toluene, Ethylbenzene and Xylene (BTEX) in those vehicles have not been investigated so far. The primary aim of this study was to determine if passengers are exposed to different BTEX levels when using buses powered by CNG or by diesel, and further explore if indoor levels are influenced by external air quality. For this purpose, BTEX air concentrations were measured in bus cabins (CNG and diesel), parking stations and in a background urban area using passive air samplers. Results showed that BTEX concentrations inside vehicles were higher than outside, but no significant differences were found between buses powered by CNG or by diesel. In CNG vehicles, high and significant positive correlation was found between benzene and the number of journeys in the same route (r = 0.786, p < 0.05), vehicle operating time (r = 0.738, p < 0.05), exposure time (r = 0.714, p < 0.05) and exposure index (r = 0.738, p < 0.05), but this was not observed for diesel vehicles. Benzene in bus cabins was found to be significantly below reference value for human health protection. However, excepting p-xylene, all other aromatic pollutants have a mean concentration significantly above the lowest effect level (p ≤ 0.002 for all comparisons). Additionally, higher BTEX levels in cabin buses than in outdoor air suggest the presence of other emission sources in indoor cabins. These findings emphasize the need for further studies to fully characterize indoor emission sources in order to minimize the negative impact of BTEX exposure to human health.
为了最大限度地减少城市地区的高排放水平，柴油燃料公共汽车已被压缩天然气（CNG）取代。然而，迄今为止，尚未研究这些车辆中室内苯、甲苯、乙苯和二甲苯（BTEX）暴露水平的差异。本研究的主要目的是确定使用 CNG 或柴油驱动的公共汽车时，乘客是否会接触到不同的 BTEX 水平，并进一步探讨室内水平是否受到外部空气质量的影响。为此，使用被动空气采样器在公共汽车车厢（CNG 和柴油）、停车场和背景城市地区测量 BTEX 空气浓度。结果表明，车辆内部的 BTEX 浓度高于外部，但 CNG 或柴油驱动的公共汽车之间没有发现显著差异。在 CNG 车辆中，苯与同一路线的行驶次数（r=0.786，p<0.05）、车辆运行时间（r=0.738，p<0.05）、暴露时间（r=0.714，p<0.05）和暴露指数（r=0.738，p<0.05）之间存在高度显著的正相关关系，但在柴油车辆中没有观察到这种关系。公共汽车车厢内的苯明显低于人类健康保护的参考值。然而，除对二甲苯外，所有其他芳香族污染物的平均浓度均明显高于最低效应水平（所有比较均为 p≤0.002）。此外，车厢内公共汽车中的 BTEX 水平高于室外空气，表明室内车厢内存在其他排放源。这些发现强调需要进一步研究，以充分描述室内排放源，从而最大限度地减少 BTEX 暴露对人类健康的负面影响。
