Exposure to BTEX in buses: The influence of vehicle fuel type

• Published in: Environmental pollution (1987) Vol. 255; no. Pt 1; p. 113100
• Main Authors: Fontes, Tânia, Manso, M. Conceição, Prata, Joana C., Carvalho, Márcia, Silva, Cláudia, Barros, Nelson
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-12-2019
• Subjects: Air Pollutants - analysis; Air Pollution; Air Pollution, Indoor - analysis; Benzene - analysis; Benzene Derivatives - analysis; Compressed natural gas; Diesel; Environmental Monitoring - methods; Humans; Indoor exposure; Motor Vehicles; Natural Gas - toxicity; Public transport; Toluene - analysis; Vehicle Emissions - analysis; Volatile organic compounds; Xylenes - analysis; Volatile organic compounds; Diesel; Public transport; Compressed natural gas; Indoor exposure
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2019.113100

Diesel-fueled buses have been replaced by Compressed Natural Gas (CNG) to minimize the high level of emissions in urban areas.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 (rs = 0.786, p < 0.05), vehicle operating time (rs = 0.738, p < 0.05), exposure time (rs = 0.714, p < 0.05) and exposure index (rs = 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.
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•Buses running on natural gas or diesel showed no differences in indoor BTEX levels.•Values suggest other emission sources of toluene and xylenes in indoor cabins.•Distinct vehicle uses and/or routines can influence indoor vehicle emissions.•BTEX in buses are below guidelines for human health, but above the lowest effect.
Main Findings: Buses running on natural gas or diesel showed no differences in indoor BTEX levels. Other emission sources of toluene and xylenes in indoor cabins are present. Distinct vehicle uses and/or routines can influence indoor vehicle emissions. BTEX are below guidelines for human health, but above the lowest effect level.