Commuter exposure and indoor–outdoor relationships of carbon oxides in buses in Hong Kong

The exposure of bus commuters to carbon monoxide (CO) and carbon dioxide (CO₂) in various bus routes in Hong Kong has been studied. The buses under investigation travel in the city of Hong Kong and involve both air-conditioned and older buses without air-conditioning. The in- and out-vehicle concentrations of both pollutants were measured simultaneously using portable samplers. It is found that the exposure level of CO₂ inside the air-conditioned vehicle is strongly dependent on the number of passengers but not on the driving environment. During the measurement, it is found that the CO₂ level can reach up to a dangerous 10 times that out-vehicle when the air-conditioned bus is full. On the other hand, it was found that the CO and CO₂ levels for a non-air-conditioned bus remain low due to better air exchange between in- and out-vehicle.