As of Wednesday, more than 400 wildfires were burning across Canada, leading to air quality alerts − indicators the air is unsafe to breathe for certain people − across much of the eastern U.S.

Smoke from wildfires in Canada has drifted into the U.S., prompting air quality alerts for Americans as it continues to spread. But when officials and forecasters classify a city's air as ...

As of 12 a.m. Thursday, the city's air quality index was over 400. White House press secretary Karine Jean-Pierre said President Joe Biden sent more than 600 firefighters and equipment to Canada.

(The index climbed higher in Chicago on Wednesday morning to 216, though the air quality was worse in Detroit, where the index hit 306.) In Green Bay, Wis., the index was 175; in Grand Rapids ...

Areas including Chatham, Ottawa and Windsor had an air quality health index of moderate, which is level 4 of 10. Those areas are also forecast to improve over the next couple of days.

Communities south of the U.S.-Canada border reported air quality index (AQI) readings between 200 and 400 – levels which are considered to be unhealthy to even hazardous. A value between 0 and ...

The Air Quality Index tracks this kind of pollution with a measurement known as PM 2.5, which quantifies the concentration of particles smaller than 2.5 micrometers in the air.

Environment Canada has been advising people to check the Air Quality Health Index as wildfire smoke blanketed large swaths of Canada in recent days. Even without wildfires, the index can be a ...

By 12:30 p.m., the Air Quality Index had reached unhealthy levels in the entire Chicago area, with AirNow.gov showing the city with an AQI of 163, the north and west suburbs with an AQI of 158 and ...

The New York State Department of Environmental Conservation’s air-quality health advisory in response to wildfire smoke wafting down from Canada is based on the Air Quality Index, or AQI.