In-cabin exposure levels of carbon monoxide, carbon dioxide and airborne particulate matter in air-conditioned buses of Hong Kong

Bus cabin air quality has not been incessantly monitored in Hong Kong. This study investigates the in-cabin exposure levels of CO, CO2 and PM10 for running buses in Hong Kong that are equipped with Euro II, III and IV engines. A representative urban-suburban bus route was chosen and there were no significantly different in-cabin CO levels reported among engine types and between rush and non-rush hours. However, in-cabin CO level was found significantly associated with ambient/roadside CO level; the former was altogether higher than the latter due to the bus' own exhaust. Regarding in-cabin PM10 concentration, the engine type played a major role. The outcome demonstrates that new buses (i.e. Euro IV) generally provide a better in-cabin environment for commuters. Therefore, implementation of an air filtration upgrade, together with a routine filter cleaning schedule, is an effective measure to ameliorate bus cabin air quality. This study also provides useful information for further investigation into the causal relationship between health risks and long-term air pollution exposure in local bus cabins.