Smoke from devastating wildfires in Canada is blanketing a large swath of the Midwest and Northeast this week, causing cities across the region to issue air quality warnings.
The extreme levels of smoke mean that even able-bodied adults would be wise to take some precautions to protect their health. The increasing severity of wildfires across the continent—driven in part by climate change—means that even places where blazes aren’t burning will still suffer the impact.
More than 100 fires are burning out of control across Canada as of Wednesday, with hundreds more being monitored or battled. The smoke has drifted south and east, turning skies hazy from Minnesota to New York. Particularly dramatic images have emerged from Toronto, where commuters went to work on Wednesday morning under orange skies. The region is also dealing with a heat wave, with temperatures well above 90 degrees Fahrenheit in many areas and an even higher heat index.
On Wednesday evening, the air quality index in New York City topped out at 180, putting the city’s air squarely in the “unhealthy” category as defined by the US Environmental Protection Agency. Other places were even worse off, with Duluth, Minnesota, seeing its AQI top out above 500. (Anything over 301 is labeled “hazardous” and considered unsafe for everyone.) Smoky conditions are expected to worsen in parts of the Northeast US on Thursday, including New York.
The wildfire smoke blanketing the area contains microscopic particles of matter known as PM2.5s—shorthand for particles that are smaller than 2.5 micrometers, or 30 times smaller than the width of a human hair.
Exposure to PM2.5s can trigger or worsen a number of medical conditions, especially in vulnerable populations. Nicholas Nassikas, a pulmonologist and assistant professor of medicine at Harvard Medical School, says that he would tell his patients with preexisting conditions, like asthma or lung disease, to limit their time outside. Children “have a faster breathing rate—they just breathe more,” says Nassikas, while the elderly, who often have compounding conditions and may live in less well ventilated homes and senior centers, are also at risk.
Jennifer Stowell, an assistant professor at the University of Maryland’s School of Public Health, says that even healthy adults may want to take precautions on days when the air quality index goes over 100: “At the very least, it is important to limit your time outdoors to reduce your overall exposure.” she says. If you have to be outside for long periods, she recommends wearing an N95 mask. Stowell, who is currently in Boston, where the AQI hit 110 on Wednesday, says she wasn’t planning on attending outdoors events until the evening.
Dan Westervelt, an associate professor of climate physics at Columbia University, is similarly cautious. “I’m going to make sure my kids are staying indoors today,” he says. “I won’t be doing any physical exertion, like running, today or tomorrow.”
Climate change is driving up temperatures. That’s making wildfire season longer and creating hotter, drier conditions that lead to more explosive fires. A study published last year estimated that wildfire smoke already causes 40,000 deaths per year in the US, and could more than double to 70,000 deaths per year by 2050 if warming continues. As bad-air-quality days from wildfire smoke get more common, the research on prolonged exposure to that smoke is still developing. A similar blast of smoke from Canadian wildfires hit the Northeast in 2023.
“Exposure to high levels of air pollution over the course of a lifetime or a long period of time is demonstrated numerous times in research to lead to premature mortality,” says Westervelt. “You can chop off some months of your life expectancy if you are living in conditions where you’re very frequently exposed to high levels of air pollution.”
