Wildfire smoke drifting across the Great Lakes has caused air quality to plunge to hazardous levels in several states, affecting millions of people in major cities.

Wildfire smoke from Canada turned Chicago into one of the world’s most polluted metro areas as the Lollapalooza music festival began.

Wildfire smoke from Canada and the western US has drifted over the Great Lakes, causing hazardous air quality in Chicago, Minneapolis, and Green Bay. Fine particles in the smoke pose health risks, especially for vulnerable groups,