The influence of passenger activities on exposure to particles inside buses

Elevated personal exposures to particles have been reported in buses, but the factors associated with these high exposures are uncertain, and the potential role of passenger activities within buses has not been quantified. To improve understanding of this factor we measured particle number concentrations in the range 0.3–15 μm simultaneously inside and outside buses in the city of York (UK), while carefully noting passenger activities. We also developed a box model to simulate the effects of passenger activities, and parameterised this from independent studies with controlled passenger activities. The number concentrations inside buses were significantly higher than those outside in all size classes, and the inside/outside ratios increased with particle size. The model showed broad agreement with measured particle concentrations inside buses, and demonstrated, for particles in the range 3–15 μm, that both re-suspension by passenger activities and deposition to the surface of the passengers had significant effects on concentrations. Hence, understanding of the effects of passenger activities on both particle deposition and re-suspension is essential to interpret exposure measurements inside buses. Exposure of regular commuters inside buses could be of potential health significance and needs further assessment.