Traffic-related volatile organic compounds (VOCs) represent an important exposure pathway for urban commuters in megacities such as Bangkok, Thailand. This study quantified personal exposure to benzene, toluene, ethylbenzene, and xylene isomers (BTEX) and evaluated associated inhalation health risks across five major transportation modes: air-conditioned bus (A/C bus), non-air-conditioned bus (non-A/C bus), taxi, the Bangkok Mass Transit System (BTS), and the Metropolitan Rapid Transit (MRT). Personal air monitoring was conducted during wet and dry seasons to capture seasonal variability in exposure. BTEX concentrations differed significantly by transport mode and season. Non-A/C buses consistently exhibited the highest concentrations, followed by A/C buses and taxis, while the lowest levels were observed in rail-based systems (BTS and MRT). Across all modes and seasons, concentrations ranged from 6.1-41.4 µg/m3 for benzene, 19.1-128.6 µg/m3 for toluene, 1.9-23.7 µg/m3 for ethylbenzene, 10.3-50.3 µg/m3 for m,p-xylenes, and 2.3-8.8 µg/m3 for o-xylene, with consistently higher levels during the dry season. Non-carcinogenic risk assessment indicated hazard index values below unity for all transport modes, with the highest value observed in non-A/C buses during the dry season (HI = 7.94 × 10-2). In contrast, benzene-related incremental lifetime cancer risks frequently exceeded the U.S. EPA lower benchmark (1.0 × 10-6) but remained below the upper tolerable limit (1.0 × 10-4), with the highest risk estimated for non-A/C bus commuters (9.80 × 10-6). These results demonstrate that transportation mode and seasonality are key determinants of commuter BTEX exposure and highlight the need for targeted mitigation strategies focusing on ventilation design, emission control, and cleaner public transport systems.Implications: This study provides policy-relevant evidence for urban air quality management and exposure reduction in traffic-congested megacities. Significant variation in BTEX exposure across transport modes indicates that microenvironmental conditions, including ventilation, cabin enclosure, and proximity to traffic emissions, strongly influence commuter exposure. Road-based modes, particularly non-A/C buses, exhibited the highest exposures and risk estimates. Although risks remained within regulatory thresholds, benzene-related cancer risks highlight routine commuting as a meaningful long-term exposure pathway. Targeted controls such as improved vehicle ventilation and sealing, VOC filtration, stricter emission standards, reduced idling, and expansion of mass rapid transit can effectively reduce commuter exposures and support evidence-based transportation and air quality policies.
Khantikulanon et al. (2026) studied this question.