Overview

• Provincial and state agencies have issued air quality health advisories from Montreal and southern Quebec through New York, Vermont, Maine, parts of New Jersey and Colorado, urging sensitive groups to stay indoors and limit outdoor exertion.
• The National Weather Service says smoke became locked near the surface by a sinking air mass on July 26–27, pushing PM2.5 concentrations into unhealthy ranges for vulnerable populations.
• Canada’s 2025 wildfire season has exceeded historical averages, with more than 550 active blazes scorching over 15 million acres and fueling sustained cross-border smoke transport.
• Forecast models suggest modest improvement in air quality by Sunday evening as winds shift, but meteorologists warn that changing wind patterns or incoming systems could funnel fresh smoke back into the region early next week.
• Montreal briefly ranked as the world’s worst city for air quality on IQAir, while Boston and New York City recorded AQI levels from moderate to unhealthy for sensitive groups this weekend.