Chicago's Air Quality Plummets to Unhealthy Levels, Causes Haze and Smoke.

Chicago currently has the worst air quality in the world, marked by the "unhealthy" red zone due to Canadian wildfire smoke coming in from northerly winds. Dubai ranks second in worst air quality, followed by Sao Paulo, Brazil. Chicagoans are advised to wear masks, run air purifiers, and avoid time outside, especially those with heart and lung diseases. Weather models suggest air quality should improve by 10 p.m. Tuesday.