"The air quality is officially dangerous in Chicago," says Brian Urbaszewski, director of environmental health programs at the Respiratory Health Association. "It's going to send people to the emergency room.

However, Lake, Porter, Newton and Jasper counties in Indiana will be under another air quality alert all day Tuesday. The Chicago area had been under air quality alerts for much of the last week, due to smoke from Canadian wildfires. At one point last week, Chicago had the worst air quality in the world.