Characterization of black carbon at roadside sites and along vehicle roadways in the Bangkok Metropolitan Region

The average on-road BC concentration (25.5 μg m−3) was similar to the average at the roadside under downwind conditions (25.5 μg m−3) from morning to evening only. In contrast, the latter value was 1.7-fold higher than the daily average at the roadside (14.7 μg m−3) and 7.3-fold higher than the urban background level during the daytime (3.5 μg m−3). The results of this study suggest that residents who live next to major roads, pedestrians at the roadside, and drivers on the roads experience a high risk of exposure to severe levels of traffic-related air pollutants.