Chicago, Milwaukee and Detroit had some of the worst air quality in the world Tuesday as wildfire smoke from Quebec, Canada, seeps into the Midwest. The raging fires have been impacting parts of the U.S. since earlier this month, and all three cities hit the purple zone of the AQI, or air quality index.

At one point on Tuesday, Chicago was at level 228, veering into the purple or "very unhealthy" zone, and nearby Milwaukee was at level 221, according to AirNow, a government site that measures air quality. 

Maps that depict the current air quality in the U.S. show Illinois, Wisconsin and parts of surrounding states like Minnesota, Iowa, Indiana and Michigan are in the red or "unhealthy" zone and some people may experience health effects, according to AirNow. 

The East Coast of the U.S., which suffered dangerous air quality from the Canadian wildfires earlier this month, now appears mostly clear, but some areas are in the yellow or "moderate" zone, which means the air quality is acceptable but could pose a risk for some people. 

According to IQ Air, which monitors the air quality index around the world, major midwestern cities Chicago, Milwaukee and Detroit had some of the worst air quality in the world, with Dubai as well as Lahore and Karachi, Pakistan, also high on the list. Chicago topped the list at times Tuesday.

The wildfires have led many cities to issue air quality alerts this month, urging people — especially those with sensitivities — to avoid going outside. New York City became blanketed in an orange haze as wildfire smoke spread across the U.S. on June 7. That day, the city ranked second in the world for worst air quality after Delhi, India. Detroit soon pushed New York out of second place.

Chicagoans woke up Tuesday to a hazy sky, shown in images from The Weather Channel. National Weather Service Chicago declared June 27 and 28 air quality action days, urging people in Chicago and Indianapolis to limit time outdoors. 

Low visibility due to wildfire smoke will continue today. Consider limiting prolonged outdoor activities. For observations and forecasts of air quality, visit https://t.co/N5S58sVQNn. #ILwx #INwx pic.twitter.com/esa7G2JVm4

— NWS Chicago (@NWSChicago) June 27, 2023

Minnesota has set a record with 23 air quality alerts in 2023, according to the Minnesota Pollution Control Agency. The state usually has two to three a season. 

NASA said Monday the smoke from Canada spread across the Atlantic to southwestern Europe. Images from NASA's Terra satellite show smoke over Portugal and Spain, but NASA said it has spread even further. 

There were 492 active fires across Canada as of Monday and 257 were burning out of control, according to the Canadian Interagency Forest Fire Centre, Wildfires in Canada throughout May and June have created a record level of emissions and many of the fires show little sign of slowing down, according to the EU's Copernicus Atmospheric Monitoring Service.

In:
• Chicago
• Wildfire Smoke

Caitlin O'Kane

Caitlin O'Kane is a digital content producer covering trending stories for CBS News and its good news brand, The Uplift.