Canadian wildfire smoke triggers air quality alerts for millions: What to know

More than 100 million Americans are under air quality alerts as smoke from wildfires in Canada and northern Minnesota blankets parts of the U.S. and releases microscopic particles into the atmosphere that can raise serious health risks.

Shifting winds have pushed thick haze into major metro areas across the Great Lakes, Northeast and Mid-Atlantic, reducing visibility, tinting skies and sending pollution levels into unhealthy and even hazardous ranges.