A fire hose of dangerous pollution from wildfires blankets the northern U.S.

A fire hose of dangerous pollution from wildfires blankets the northern U.S.Smoke from northern Minnesota and western Ontario wildfires is pouring over the Great Lakes, mid-Atlantic and Northeast, bringing record levels of hazardous air pollution to major citiesBy Andrea Thompson edited by Claire CameronSmoke from wildfires in Minnesota and Ontario pour over the Great Lakes and New York on Wednesday, July 15. NOAAWildfires in Minnesota and Ontario are spewing dangerous smoke into the air that is posing a major air pollution threat to millions living in major cities such as Detroit, Milwaukee, Cleveland, Philadelphia and New York City. As of Thursday morning, Detroit, Toronto and Minneapolis had the highest air pollution levels in the world. Chicago and New York City were in the top 10. Minnesota set a record for the state's highest-ever wildfire smoke concentration on Wednesday morning.The area of high pressure that is causing yet another heat dome over the central U.S. is resulting in a clockwise flow of air is pushing wildfire smoke down to ground level and toward the southeast over the next couple of days. People in its path could experience unhealthy to hazardous levels of PM2.5 pollution—small, dangerous particles in smoke that can be breathed deeply into the lungs. For context, in the color-coded Air Quality Index, red indicates “unhealthy,” while maroon indicates “hazardous.”READ MORE: How to Use the Air Quality IndexOn supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Exactly how high the pollution levels will be and how long poor conditions may last in any given location is still somewhat uncertain: “Forecasting wildfire smoke is HARD, and model forecasts are often way off—either high or low,” wrote meteorologist Jeff Masters in a Bluesky post. “The models are in their infancy, and have to get the meteorology, fire behavior and atmospheric chemistry right.”Smoke is also making for hazy orange skies because the particles tend to scatter blue light but allow orange and red wavelengths to pass through.The fires in Minnesota are unusual for this time of year, which is generally a wet period—fire season typically comes in spring or fall. But drought and exceptionally hot weather have left vegetation parched, which has made it primed to burn with any spark. Some such sparks came from lightning that passed through the Boundary Waters Canoe Area Wilderness (BWCA) and other areas of the Superior National Forest last week. Steady winds have fanned the flames. On Tuesday the blazes tore through 33,000 acres of land, jumping across rivers and lakes and the border with Canada. The BWCA and parts of the forest have been closed to visitors and campers are being evacuated from the BWCA, and Minnesota’s governor Tim Walz has declared an emergency to allow the National Guard and other resources to assist with the fires.Air pollution levels ranged from "unhealthy" (red) to "hazardous" (maroon) across a broad swath of the Midwest and Northeast on the morning of Thursday, July 16.AirNow.govFires also erupted across Ontario on Tuesday and Wednesday because of hot, dry conditions, causing evacuations of rural and First Nations communities near Thunder Bay and pouring more smoke into the atmosphere.The smoke from the fires could pose an air pollution problem periodically over the next 10 days, Masters notes. Particulate pollution is particularly a risk for young children, older people, and those with heart and lung conditions. The best way to protect yourself from smoke is to limit time spent outdoors, wear an N95 mask when you do have to be outside and when air pollution is high, keep doors and windows closed and well sealed and run air purifiers inside.Editor’s Note (7/16/26): This story was updated with new information on the state of the fires and forecast.It’s Time to Stand Up for ScienceIf you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. 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