Chicago's Air Quality Ranked Worst in the World Due to Wildfire Smoke.

Chicago and Milwaukee have the worst air quality in the world due to wildfire smoke from Quebec, Canada, seeping into the Midwest. The air quality index in Chicago was at level 228, veering into the purple or "very unhealthy" zone, and nearby Milwaukee was at level 221. The East Coast of the U.S. appears mostly clear, but some areas are in the yellow or "moderate" zone. The wildfires have led many cities to issue air quality alerts this month, urging people to avoid going outside.