Associations between classroom ventilation rates and school characteristics with indoor air in classrooms during wildfire smoke events.

In this study, we were interested in understanding what school-level factors influence infiltration of wildfire smoke into schools. This is important given that wildfire smoke is increasingly affecting western North America and has been found to affect children's respiratory health. We first determined air change rates, measured in air changes per hour (ACH), in 17 schools under four ventilation scenarios using controlled release carbon-dioxide (CO2) decay testing. We also investigated to what extent school-level characteristics and air change rates under the four ventilation scenarios influenced indoor/outdoor (I/O) particulate matter (PM) ratios across schools during a wildfire smoke-impacted period in May 2023 to determine if and how those characteristics impact PM infiltration into schools. Based on our findings, some schools (most of them without central heating, ventilation, and air-conditioning (HVAC) systems) can only achieve recommended air exchange rates for school classrooms with their windows open. During wildfire smoke events, these classrooms would likely have to choose between protecting students from wildfire smoke by keeping windows closed or achieving the standard of air exchange rates. We also found that natural air change rate and building age were positively associated with I/O PM ratios, whereas the presence of central HVAC systems was negatively associated with I/O PM ratios during a wildfire smoke event. This finding points to the need for central HVAC systems to protect against wildfire smoke and to achieve necessary air exchange rates within school classrooms.