Analysis of impact of ventilation and air cleaning strategies on classroom PM2.5 and CO2 under normal and wildfire conditions – A CONTAM simulation study

Particulate matter (especially PM₂.₅) and carbon dioxide (CO₂) are key indicators of indoor air quality (IAQ). This study uses a multizone model (CONTAM) to simulate PM₂.₅ and CO₂ concentrations for representative ventilation scenarios with or without portable air cleaners (PACs) in a K-5 school during normal and wildfire conditions. The CONTAM model mimicked the measurement setup, consisting of one hallway and eight mechanically ventilated classrooms, each having approximately 20 students. After validating the model against measurement data, 50 more scenarios were simulated, changing ventilation conditions (mechanical vs. natural ventilation) and PAC operations, under both normal conditions and wildfire conditions. Simulation results indicate that under normal conditions, HVAC system operating at 12 h -1 with 20% outdoor air and a MERV 8 filter maintained average PM₂.₅ and CO₂ concentrations below 5 µg/m³ and 1,000 ppm, respectively. Using a MERV 13 filter further reduced PM₂.₅ concentrations to 3 µg/m³. During wildfire conditions, when outdoor PM₂.₅ reached 30 µg/m³, indoor PM₂.₅ levels were over 10 µg/m³ for the same HVAC setup with a MERV 8 filter. Under the natural ventilation condition, indoor PM levels followed outdoor levels within 2 hours without PACs. During wildfire, operating PACs is highly recommended. Opening a door facing outdoors with one window open quickly increase indoor PM₂.₅ and CO₂ concentrations by outdoor levels, while opening a door facing hallway did not. These findings highlight the importance of reducing outdoor air intake and utilizing effective filtration strategies to mitigate wildfire-related impacts on IAQ in schools.