The Northeast Is Being Blanketed in Canadian Wildfire Smoke

Smoke from wildfires burning in Canada has spread across a large part of the United States this week. Cities in the Midwest and Northeast are warning residents that the air is unhealthy to breathe. More than 100 fires are burning out of control in Canada, and hundreds more are being watched or fought by firefighters. The smoke has drifted south and east, turning skies orange and hazy from Minnesota all the way to New York.

The air quality index, or AQI, measures how clean or polluted the air is on any given day. On Wednesday evening, New York City's AQI reached 180, which falls in the 'unhealthy' category according to the U.S. Environmental Protection Agency. In Duluth, Minnesota, the AQI topped 500 — well above the 301 level that is labeled 'hazardous' and considered unsafe for everyone. Experts say smoky conditions are expected to get even worse in parts of the Northeast on Thursday.

The smoke contains tiny particles called PM2.5. These particles are smaller than 2.5 micrometers, which is about 30 times thinner than a human hair. Because they are so small, they can travel deep into a person's lungs and cause serious health problems. People who already have conditions like asthma or lung disease are especially at risk.

Doctors and health experts are urging people to stay indoors as much as possible. Nicholas Nassikas, a lung doctor and professor at Harvard Medical School, says children breathe faster than adults, which means they take in more of the harmful particles. Older adults are also at high risk because they may have other health conditions and sometimes live in places with poor ventilation. Nassikas recommends that people with breathing conditions avoid going outside on days with heavy smoke.

Even healthy adults should take care when air quality is poor. Jennifer Stowell, a professor at the University of Maryland's School of Public Health, says that when the AQI goes above 100, everyone should try to spend less time outdoors. She also recommends wearing an N95 mask if you must be outside for a long time. Stowell herself was in Boston, where the AQI hit 110 on Wednesday, and she decided to skip outdoor events for the day.

Climate change is making wildfires more frequent and more powerful. Rising temperatures create hotter, drier conditions that help fires spread faster and burn longer. A study published last year found that wildfire smoke already causes about 40,000 deaths per year in the United States. Scientists warn that number could rise to 70,000 deaths per year by 2050 if the planet keeps warming.

Researchers like Dan Westervelt, a professor at Columbia University, say the long-term effects of breathing smoky air are very serious. He says that people who are regularly exposed to high levels of air pollution over many years can lose months off their lives. Westervelt said he plans to keep his own kids indoors and will not go running or do other hard exercise until the smoke clears. He called wildfire smoke the biggest air quality challenge the country faces today.

Wildfire smoke can be especially toxic when fires burn through towns and neighborhoods. When homes, cars, and playgrounds catch fire, the smoke contains a harmful mix of chemicals — not just ash and soot. N95 masks can block some of the tiny particles, but they cannot filter out all the dangerous gases found in wildfire smoke. This makes the smoke from structure fires even more dangerous than smoke from forest fires alone.

New York City has opened cooling centers to help residents deal with a heat wave hitting the region at the same time. Some centers are handing out free masks. However, experts point out that masks do not block gaseous pollutants, and cooling centers may not all have air purifiers running. Experts say these centers should also focus on providing clean air, not just a cool place to sit.

The United States has made a lot of progress over the years in reducing pollution from cars and power plants. Scientists say the country has done a good job making vehicles more efficient and switching to cleaner energy sources. But now, wildfire smoke is undoing some of that hard work. Experts say that tackling wildfires — which are fueled by climate change — is the next big challenge for keeping the nation's air clean.