Efficiency of portable air purification on public buses: A pilot study

High concentrations of fine particulate matter (PM_2.5) have been frequently reported in public transit systems and can cause adverse health effect. The portable air purifier is an inexpensive solution that could potentially clean in-cabin PM_2.5. This study aims to find the PM_2.5 removal efficiency of portable air purifiers in a public transit bus. In various scenarios, after artificially preloading the in-cabin PM_2.5 concentration to 400 μg/m³, the concentrations were measured every 10 s, with and without the intervention of air purifiers. In a test bus with a volume of approximately 62.5 m³, three portable air purifiers were capable of reducing the average concentration of PM_2.5 by 42-74%, from 400 μg/m³, to levels below 15 μg/m³, the acceptable short-term exposure concentration recommended by WHO. When high concentrations of outdoor PM_2.5 entered the bus, purifiers maintained a relatively low level of in-cabin PM_2.5. Air purifiers were more effective in reducing in-cabin PM_2.5 than traditional air filtration and ventilation methods (air conditioning system filtration and door opening) in public transit buses. The deployed air purifiers reduced the concentration of particulate matter inside the bus, which may reduce the health risk of PM_2.5 exposure and the spreading of airborne infections in public transit, thus, implying the potential to enhance passengers' and drivers' health.