Smoke from the raging wildfires in northern Minnesota drifted into Ontario on that day . Environment Canada reported areas in Ontario among the worst globally for air quality on some days . The region’s urban centers faced urgent warnings about hazardous air from the distant fires . Prolonged dryness and strong winds helped wildfires spread at breakneck speed through Minnesota and nearby states. Harmful air drifted north, blanketing Canada in a persistent layer of contaminants.