Wildfires and health: With the US and Canada blanketed by smoke, what are the risks?

Thick smoke from Canadian wildfires has blanketed Toronto, Detroit, Minneapolis, Chicago, New York, and Washington, DC, in July. At points, Detroit, Toronto, and other North American cities ranked among the worst in the world for air quality.1In several cities, monitors recorded fine particle pollution at or above levels the US Environmental Protection Agency (EPA) classifies as “hazardous” on its air quality index.2 EPA’s updated particulate matter of 2.5 μm diameter or smaller (PM2.5) breakpoints put the hazardous category at 225.5 µg/m3 and above. During July, Reuters reported hazardous readings in Minneapolis, Milwaukee, and Toronto, while state and local monitors recorded PM2.5 concentrations above 600 µg/m3 in parts of Minnesota and Wisconsin.3Some US politicians took to social media, blaming Canada as summer activities were curtailed and residents were warned to stay indoors. And in a reversal, wildfires in the US west are now sending smoke north across the border into British…