Air quality alerts can change quickly during wildfire smoke events. Here’s what Code Orange, Code Red, Code Purple and Code Maroon mean, and when you should limit time outside.

Millions of people from the Great Lakes to Washington, D.C., are breathing hazardous air as smoke from hundreds of wildfires in Canada and Minnesota spreads across the region.

Dangerous wildfire smoke is filling the skies from the Midwest to the Mid-Atlantic.