As more than 800 wildfires burn across Canada, including dozens of out-of-control fires in western Ontario, the resulting smoke has worsened air quality in several parts of the United States, including the Great Lakes, the Midwest and the Northeast. Disturbing images of orange skies over New York City on Wednesday and Thursday sparked widespread concern
As more than 800 wildfires burn across Canada, including dozens of out-of-control fires in western Ontario, the resulting smoke has worsened air quality in several parts of the United States, including the Great Lakes, the Midwest and the Northeast.
Disturbing images of orange skies over New York City on Wednesday and Thursday sparked widespread concern and confusion about the risks posed by poor air quality.
To determine air quality, the Environmental Protection Agency (EPA) uses the Air Quality Index or AQI. The scale goes from 0 to 500. A higher AQI value means a higher level of air pollution and a greater health risk.
NYCEM, the city’s emergency management agency, forecast an AQI of 200 in New York City on Thursday. In areas like Detroit, it hit 754 Thursday morning, according to air quality tracker IQAir. (EPA’s official guidance classifies any AQI above 300 as hazardous, but in cases like wildfires or other extreme situations, the IQAir scale can exceed 500.)
Poor air quality can cause a litany of symptoms, including coughing, wheezing, itchy eyes, headaches, chest pain, runny nose, and more. It can also cause chronic inflammation.
Here’s a complete guide to the AQI scale, including what the numbers mean and how you can protect yourself from harmful air pollutants during a wildfire.
0-50: Good
According to AirNow, a website and app managed by the EPA, an air quality index of 50 or less means satisfactory air quality.
Air of this quality poses little or no risk to humans. People who inhale air that falls at this point on the AQI are very unlikely to experience health problems as a result.
51-100: Moderate
The EPA considers air between 51 and 100 AQI “acceptable.” People who are particularly sensitive to air pollution may be at risk by inhaling air of this quality.
According to the EPA, people with heart or lung disease, people with diabetes, older adults, and children are groups generally more sensitive to air pollutants.
101-150: Unhealthy for sensitive groups
Members of sensitive groups may experience health effects, while the general public is less likely to be affected.
151-200: Unhealthy
The general population is more likely to experience health problems and sensitive groups are at risk of serious health problems.
201-300: Very unhealthy
The high risk of health problems extends to the general public at this AQI level.
301-500: Dangerous
Everyone who inhales air with an AQI between 301 and 500 will likely be affected by poor air quality.
Smoke from wildfires in Canada covered the Manhattan skyline on July 15, 2026. Bloomberg/Bloomberg/Getty Images
How can I protect myself from air pollutants?
As Business Insider previously reported, there are ways to protect yourself when air quality is particularly bad. These include staying inside and closing windows. You should also avoid certain indoor activities, such as lighting candles or making fires, which increase indoor pollution, and vacuuming, which can stir up fine particles that have entered the home.
If you must go out, wearing an N95 mask can help filter the air you inhale.
“If you have to push yourself, push yourself less. Hydrate more,” Dr. Leonardo Trasande, who studies environmental health at New York University, told The Associated Press.
Elana Klein contributed to an earlier version of this story.