What Research Tells Us About Wildfire Smoke Inside Schools
A 2025 study published in the Journal of Exposure Science & Environmental Epidemiology by Dr. Orly Stampfer, Dr. Catherine J. Karr, and colleagues at the University of Washington and Washington State Department of Health looked at how wildfire smoke moves inside school buildings and childcare facilities, and what tools work best for tracking it. Their findings offer useful context for families and schools heading into wildfire season.
How Much Wildfire Smoke Actually Gets Inside Schools?
Researchers measured PM2.5 (fine particle) concentrations indoors and outdoors at four Washington State schools during wildfire smoke events in 2020 and 2021. One finding worth understanding: indoor PM2.5 levels during those events varied by as much as 49.6 µg/m³ between different rooms inside the same building. That range matters because the EPA's threshold for air that may affect sensitive groups sits at 35 µg/m³. Some rooms were well within safe limits. Others were not.
The ratio of indoor to outdoor air quality also differed widely across schools, ranging from 0.22 to 0.91. In practical terms, some buildings filtered out most of the outdoor smoke while others let in nearly all of it. Building age, ventilation type, and HVAC filters all play a role. Checking a regional AQI reading gives a general picture of outdoor conditions, but it does not reflect what is happening inside a specific building on a specific day.
Why This Is Relevant Beyond the Pacific Northwest
Wildfire smoke now affects air quality across most of the continental US each summer and fall, not only in western states. Fine particles from wildfire smoke are small enough to travel long distances and to move through building ventilation systems. Research has linked repeated PM2.5 exposure in children to respiratory irritation, increased asthma symptoms, and more frequent school absences.
The study also found that real-time sensor data, updated every few minutes, was far more useful for making decisions about indoor activities than hourly averages. A 10-minute reading predicted indoor air quality over the next hour much better than a 3-hour average did. For schools and childcare facilities trying to decide whether to hold outdoor recess or keep students in a specific wing of the building, that kind of up-to-date information makes a meaningful difference.
Low-cost air quality sensors have improved considerably in recent years, and this research provides a practical framework for how schools can use them during wildfire season. If your child's school does not yet have indoor air quality monitoring in place, it is a reasonable question to raise with facility staff.
Understanding the Air Quality in Your Own Home
The same dynamics that affect schools apply at home. During wildfire smoke events, indoor PM2.5 levels depend on how well your home filters outdoor air, how often doors and windows are opened, and whether you have any air filtration running. EezyAir offers a no-cost indoor air quality assessment to help homeowners understand their baseline and identify any areas of concern.
Your Free Indoor Air Assessment Takes About 16 Minutes -> Start Now
This post is for educational purposes and is based on published peer-reviewed research. It is not intended as medical advice. Consult a healthcare professional for guidance specific to your family's health.
