A thick blanket of smoke from massive Canadian wildfires has engulfed Chicago, pushing air pollution to hazardous levels and prompting health officials to advise residents to remain indoors. On Thursday, Chicago recorded hazardous air quality, placing it among the world's most polluted major cities as smoke spread across the Midwest and Northeast.
The smoke has affected more than 125 million people, disrupting travel, sporting events and daily activities. Authorities expect conditions to persist through Friday before gradually improving.
