Concentrations and risk assessment of selected monoaromatic hydrocarbons in buses and bus stations of Hangzhou, China

Air pollution surveys of ten selected monoaromatic hydrocarbons (MAHCs) were conducted in buses and bus stations in Hangzhou, China. The mean concentrations of MAHCs in the air of buses and bus stations were 95.9 and 36.5 μg/m3, respectively, of which toluene was the highest in all the sampling sites. Mean concentrations of all MAHCs in buses were statistically higher than those nearby bus stations (p < 0.05). MAHCs concentrations in buses largely depend on vehicle conditions (including vehicle type, fuel type, interior decoration, etc.) and traffic conditions (mainly traffic density). Among the investigated buses, microbuses had the highest MAHCs level, while electric buses had the lowest. Buses driven in downtown had the highest MAHCs level, followed by those in suburban areas and tourist areas. The mean concentration ratio of toluene to benzene was 2.1 ± 0.9, indicating that vehicle emission was the dominant source of MAHCs. Interior decorations, such as painting and surface coating, could also contribute to the MAHCs in the buses. The mean lifetime carcinogenic risks for passengers and bus drivers were 1.11 × 10− 5 and 4.00 × 10− 5, respectively, which were way above the limit set by USEPA. The health risk caused by MAHCs in bus microenvironment should be cautioned.