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Indoor Air Traps Wildfire Smoke: Chicago Alert
21 Jul
Summary
- Air conditioning units may trap hazardous wildfire smoke particles indoors.
- Indoor air quality in Chicago apartments remained high during smoke events.
- New sensors are being used to study long-term health impacts of pollution.

Wildfire smoke caused significantly hazardous indoor air quality in Chicago apartments last week, even as outdoor skies began to clear. Data from sensors in multiple multi-family buildings revealed that particulate matter levels inside homes were alarmingly high, with some readings reaching 340 AQI when outdoor levels peaked between 600-700 AQI.
Experts noted a common misconception that air conditioning systems filter outdoor air, when in reality, they often recirculate particles already present indoors. Alertify, a sensor company, tracked data showing these elevated indoor levels persisting even as outdoor conditions improved.
To combat this, recommendations include upgrading home air filters to a higher efficiency, such as a 13 or 14 rating, to better capture fine particulate matter.
In response to the growing concern, organizations are collaborating with the Chicago Department of Public Health on a project to study the long-term health impacts of prolonged pollution exposure. Hundreds of sensors are deployed throughout the city to monitor pollution particles similar to those from wildfires.