Lake Bluff residents lost access to their public library Thursday, July 16, after Canadian wildfire smoke pushed air quality inside the building to what the library called "extremely poor" levels.

The Lake Bluff Public Library announced the closure on its website, saying it would remain shut all day Thursday and that Friday hours depend on whether conditions improve. No reopening decision had been made as of Thursday's announcement.

Wildfire smoke from Canada and Minnesota blanketed northern Illinois Thursday morning, according to the National Weather Service. The Chicago Tribune reported that particulate matter in the Chicago area reached an Air Quality Index of 267 on a scale of 500. Lake County was explicitly named among Illinois areas hitting that "very unhealthy" threshold.

At 9 a.m. Thursday, Chicago ranked as the fourth most-polluted major city in the world, behind Detroit, Toronto and Minneapolis, according to Swiss air quality monitoring firm IQAir.

What it means for Lake Bluff patrons

The library's closure affects anyone who planned to use the building Thursday for books, computer access, children's programming or meeting space. The library said it is continuing to monitor indoor air quality and will post updates on its website.

Hours for Friday, July 17, remain undetermined. Patrons should check the library's site before making a trip.

Health guidance

The Illinois Environmental Protection Agency recommended that all residents limit physical activity outdoors when the AQI exceeds 150. The agency also advised closing windows and doors.

AirNow, the federal air quality tracking site, classifies readings between 201 and 300 as "very unhealthy," meaning everyone faces increased health risk. People with heart or lung disease, older adults, children and teens face the highest danger and should avoid outdoor physical activity entirely, per AirNow guidance cited by the Tribune.

The primary pollutant driving Thursday's readings is PM2.5, fine particulate matter small enough to settle deep in the lungs and cross into the bloodstream. Wildfires are a major source of PM2.5, and initial exposure can cause burning in the eyes and nose.

What's next

The library said it will base its Friday decision on air quality readings inside the building. Residents can check lakeblufflibrary.org for updates or monitor regional conditions at airnow.gov.