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.