Field investigation of air quality in university shuttle buses

This field study focused on the investigation of air quality in the Harvard University shuttle bus system. Passenger exposures to carbon monoxide (CO), carbon dioxide (CO₂), and particulate matter (PM) were monitored using continuous air sampling methods. Additionally, a passenger questionnaire was administered in order to access passenger perception to perceived air quality (PAQ). The following particle continuous measurements were taken every minute: 1) PM_2.5 and PM₁₀ particle mass concentration for particles with aerodynamic diameters less than 2.5 μm and 10 μm respectively; 2) total particle number concentration for ultrafine particles with aerodynamic diameter smaller than 100 nm. The study found that the CO level was always very low; while the levels of CO₂ and PM were obviously influenced by the penetration of ambient air and particles into the bus environment, especially when the doors were open to load/unload passengers. Furthermore, the CO₂ lever was greatly affected by occupancy conditions, as it was expected. It was also worth to point out that there is a direct correlation of occupancy condition and passenger perception to PAQ. It was shown that the heavier the occupancy load the lower the passenger perception to PAQ was. The elevated CO₂ level indicates that the present in-bus ventilation system is not sufficient to dilute air pollutants produced by passengers. This lack of sufficient ventilation in the bus is an indicator of an elevated risk for airborne transmitted diseases in this transportation system.