Impact and benefits of the air cleaning measures implemented in two schools

A Canadian provincial government has initiated a collaboration with the Indoor Air Quality (IAQ) team of the National Research Council of Canada (NRC) to conduct a controlled intervention study to determine the effectiveness of portable air cleaners (PACs) in reducing indoor air contaminants in 2 schools. The study examined the presence of particulate matter of 1-, 2.5-, and 10-micron diameters (PM1, PM2.5, and PM10), carbon dioxide (CO2), and sick days reported by staff and students under various operating conditions to determine if PACs could make a statistically significant difference in these IAQ and health indicators. This paper describes the study methods and the following key findings: 1) The indoor CO2 concentrations were dependent on the presence of occupants and the leaks/openings through the building envelope in the space. Higher CO2 concentrations were measured in classrooms with higher occupant densities. The CO2 concentrations measured in both schools agreed with CO2 concentration metrics predicted based on occupant characteristics and ASHRAE 62.1 ventilation requirements. 2) The outdoor particle sources played the most significant role in deciding the indoor particle concentrations. The presence of exterior walls and windows in a space also affected the indoor particle concentrations. 3) A particle removal efficiency index was defined and used to assess the effectiveness of filtration in removing particles. Based on the PM1 and PM2.5 removal efficiency results, the PAC units in the intervention school were able to remove some of the particles entered indoors.