Measurements and monitoring of volatile organic compounds (VOCs) have been conducted in the metropolitan Bangkok. However,
in-vehicle levels of VOCs are still lacking. This study investigated VOCs concentrations in four public transportation modes in Bangkok,
Thailand during two rush hour periods (7:00–9:00 a.m. and 4:00–7:00 p.m.). The four modes included an air-conditioned bus (A/C bus),
non-air-conditioned bus (non-A/C bus), electric sky train, and a passenger boat traveling along the canal. Comparison among three
important bus routes was also studied. In-vehicle air samples were collected using charcoal sorbent tubes and then analyzed by a gas
chromatography-mass spectrometer. Results showed that the transportation modes significantly influenced the abundance of in-vehicle
benzene, toluene, ethylbenzene, and m,p-xylene (BTEX). Median concentrations of BTEX were 11.7, 103, 11.7, and 42.8 g/m3 in
A/C bus; 37.1, 174, 14.7, and 55.4 g/m3 in non-A/C bus; 2.0, 36.9, 0.5, and 0.5 g/m3 in sky train; and 3.1, 58.5, 0.5, and 6.2 g/m3
in boat, respectively. Wilcoxon rank sum test indicated that toluene and m,p-xylene in the sky trains were statistically lower than that
in the other three modes at a p-value of 0.05. There were statistical di erences in TEX concentrations among the bus routes in the
non-A/C buses. In addition, the benzene to toluene ratios implied that tail-pipe emissions were important contributor to the abundance
of in-vehicle VOCs.