Determining a commuters’ exposure to particle and noise pollution on double-decker buses

Abstract

This study evaluates a passenger’s exposure to particles and noise on Singapore’s double-decker buses when choosing to travel on the upper or lower deck. Clean and calm journeys are vital to make public buses a choice mode of transport. In the case of Singapore, as in many other cities, double-deckers are in common use and comprise a large fraction of the total public transport ridership. Exposure to noise levels and concentrations of fine particles (PM2.5 ), equivalent black carbon (eBC) and number of particles (as a proxy of ultrafine particles, UFP) were simultaneously measured on both decks. Concentrations of particle-bound polycyclic hydrocarbons and particles’ active surface area were also measured to investigate the combustion fingerprint of the particles and their average size. Concentrations of PM2.5 on the upper deck exceeded up to 50% (18 µg m–3 ) those on the lower deck. Concentrations of eBC were higher on the upper deck up to 12% (0.6 µg m–3 ), but on occasions were 40% (0.9 µg m–3 8%, 1000 # cm~) lower. In contrast, UFP often measured in slightly higher concentrations (–3 5 dBA higher downstairs. Particle loads responded to the intake of outdoor air by the air conditioning system, while sharp increases were observed on both decks every time the doors were opened to pick up and drop off passengers. In the case of the assessed route, which started and ended in fully enclosed terminals, the infiltration of particles emitted by arriving and departing buses contributed critically to the loads of PM~) on the lower deck. Noise levels were always2.5 on the upper deck. Improvements in the ventilation system on both decks, changes in engine operation at bus terminals, and faster boarding at bus stops through better coordination of bus services will reduce the load of particles to which passengers are exposed on double-decker buses.