Massive wildfires raging in eastern Canada are sending huge plumes of smoke across the border, blanketing thousands of square miles in the Northeastern U.S. and Upper Midwest, and casting a haze over skies from Wisconsin and Minnesota to New York. Hundreds of out of control fires are currently burning in Quebec, while authorities have managed to contain two wildfires burning in Nova Scotia. All that smoke isn’t a mere nuisance—it’s a legitimate health hazard, with the widespread plumes prompting air quality alerts from state health agencies.
A burning wildfire produces many different kinds of particles, many of which aren’t great for your health. But what health authorities and researchers spend most of their time worrying about are those particles with a diameter of less than 2.5 micrometers, known as PM2.5—for reference, human hairs range in width of between 17 and 180 micrometers. Our bodies have defenses like nose hairs designed to keep particles from entering our lungs when we breathe, but tiny PM2.5 particles are small enough to get past those barriers and settle in the lungs, which is why they’re of particular concern. From there, they may be able to enter the bloodstream, potentially damaging other parts of the body.
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That’s why air quality alerts may warn residents to stay indoors when PM2.5 levels are high, and especially stress that people should avoid exercising outside under such conditions in order to limit how much PM2.5 they breathe deep into their lungs. This is particularly important for children, older people, and those with preexisting heart or lung problems. In the short term, being exposed to such particles can irritate your eyes, throat, nose, and lungs, and it can also cause you to cough and sneeze, or feel short of breath. It can also cause more serious effects, like triggering asthma attacks. When PM2.5 levels increase, studies have shown that heart and lung issues tend to increase as well.
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Long term exposure, as in cities where people are exposed to PM2.5 in smog, is especially dangerous. It’s been shown to impair children’s lung development, and it can increase your risk of developing lung cancer or heart disease. For people with chronic heart or lung issues, long term exposure to PM2.5 can increase risk of death.
PM2.5 is a serious public health concern around the world, and in the U.S. policymakers have imposed regulations to limit people’s exposure—particularly though the U.S. EPA. The result has brought deep cuts to PM2.5 levels. The notable exception, though, has been PM2.5 from wildfires. Despite reductions in PM2.5 emissions across the country, wildfires are leading to an overall increase in PM2.5 levels in the U.S. Northwest, which is particularly prone to wildfires. That air pollution from wildfires, like what much of the U.S. has seen in recent days, is projected to increase in years ahead as climate change brings hotter, drier conditions that make intense wildfires more likely.
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Air quality standards typically don’t distinguish risks based on the source of the PM2.5. But there’s worrying evidence that PM2.5 from wildfires may be more dangerous than other varieties of the pollution. That evidence comes from preliminary studies on mice, and researchers aren’t sure what’s causing the effect, though they think it may have to do with the chemical properties of wildfire smoke that cause more inflammation and toxic buildup in the lungs.
None of that is likely to provide much comfort to the millions of people affected by smoke from the recent Canadian wildfires. The best advice, though, is to be aware of the risks and check for updates and guidance from local health authorities about how to best protect the health of family and loved ones. If local officials say it’s best to stay indoors, make sure to keep doors and windows closed to help keep pollution from getting inside. Home air purifiers can also help. And if you have to go outside, wearing an N95 mask can be a good option to protect yourself.
