The Chicago area recorded ozone levels of 156 late Monday afternoon. Levels above 100 are considered unhealthy. Residents with respiratory issues, children and the elderly are advised to stay indoors and limit exposure to air outside until Tuesday evening.

Smoke from wildfires in Manitoba, a Western province facing its worst fire season in 30 years, has created hazardous air quality conditions across Eastern Canada and the United States.

Environment Canada urges residents to limit their time outdoors. But even when inside, most buildings can only reduce airborne pollutants by half.