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Chicago Air Quality: Smoke Lingers Indoors
22 Jul
Summary
- Smoke particles from Canadian wildfires may still be circulating indoors.
- Indoor air quality reached hazardous levels during the smoke event.
- High-efficiency filters are recommended for central air systems.

Chicago has seen a marked improvement in outdoor air quality after being blanketed by Canadian wildfire smoke last week. The city's ranking on global air quality lists has significantly dropped, signaling clearer skies. However, health experts warn that the danger may persist indoors.
Particles from the wildfire smoke can remain trapped in homes, circulating through air conditioning systems that lack adequate filtration. Studies revealed alarmingly high levels of indoor particulate matter, comparable to hazardous outdoor conditions experienced recently. These fine PM2.5 particles pose serious health risks.
Many people misunderstand air conditioning units, believing they automatically filter smoke. In reality, without specialized filters like MERV 13 or higher, these systems can recirculate smoke. Experts recommend setting AC units to recirculate and closing fresh air intakes to improve indoor air quality.