"Canadian Wildfire Smoke Causes Hazardous Air Quality Alerts in US and Canada"

Smoke from Canadian wildfires has caused hazardous air quality across the US and Canada for a third day, with warnings to limit outdoor activities and stay inside. Over 400 blazes are burning in Canada, with a third in Quebec, and the smoke has reached as far as North Carolina and northern Europe. The smoke is expected to persist until the weekend, with air quality alerts extended in some areas. The poor air quality has caused delays and cancellations in travel, sports, and entertainment, and raised concerns about health effects. The fires have displaced 20,000 people, and the US has sent over 600 firefighters to help. Canadian officials say this could be the country's worst wildfire season ever, with the fires intensifying due to climate change.