The air quality in Boston is currently bad primarily due to smoke and smog caused by extensive wildfires burning in Canada. This smoke travels south and blankets the city, resulting in significantly elevated levels of particulate matter (PM2.5) and ozone pollution, both of which are harmful to human health. The Boston Real-time Air Quality Index (AQI) has reached unhealthy levels, indicating that the air contains toxic dust particles. Health officials recommend minimizing outdoor activities, wearing masks, and keeping windows closed during this period. In addition to wildfire smoke, Boston's air pollution typically comes from a mix of commercial, residential, and transportation sources, with commercial emissions being the largest contributor. Despite improvements over time due to regulations, Boston still experiences occasional unhealthy pollution days, partly aggravated by ozone pollution which causes respiratory irritation and other health risks. The current spike in poor air quality is expected to improve gradually as the wildfire smoke clears over the coming days, but the wildfire season in Canada lasts through October, so episodes may recur. Overall, Boston's air quality issues recently stem from a combination of local pollution sources and the transboundary smoke pollution transported from active wildfires in Canada.
