Effects of air purifiers and ventilation on particulate matter concentration at semi-outdoor space

We investigated the effects of air purifiers and ventilation on the particulate matter PM2.5 concentration of a semi-outdoor bus terminal using computational fluid dynamics (CFD) simulations. As per the numerical simulation results, the air purifiers alone significantly reduced the PM2.5 concentration of the bus terminal. The effect of mechanical ventilation units on the PM2.5 reduction is positive without air purifiers but negative with air purifiers. To understand the role of ventilation on the PM2.5 reduction, a simple theoretical model was derived based on the mass conservation of the PM2.5. This model considered the effects of traffic-related PM2.5 emission, air purifiers, and ventilation. The PM2.5 concentrations predicted by the proposed model showed good correlation with those from the CFD simulations. Using the model, we suggested that the ratio of the mass emission rate of PM2.5 to the clean air delivery rate of air purifiers is an important value in determining the effect of ventilation. Moreover, when the background PM2.5 concentration is higher than this value, the ventilation should be limited to reduce the PM2.5 concentration of the bus terminal. An additional CFD simulation showed that limiting the ventilation using walls can reduce the PM2.5 concentration of the bus terminal by 28.6% on average and up to a maximum of 44.2%. The present approach may be useful in improving the health of many commuters by designing openings of bus terminal and efficiently operating mechanical ventilation units.