Wildfires have burned a record of 20 million acres across Canada so far this year, with no end in sight. There are currently 500 active wildfires throughout the country and more than 250 have been deemed out of control, according to the Canadian Interagency Forest Fire Center. The smoke has been making its way to the U.S. for over a month.
Here's how the news is developing. All times Eastern.
Jun 28, 2023, 8:59 AM EDT
Where the wildfire smoke is concentrating and why
Winds at the mid-levels of the atmosphere are causing the Canadian wildfire smoke to concentrate over a specific area of the midwestern and eastern U.S.
Meanwhile, a heat dome that’s been causing stagnant deadly heat in the Deep South for weeks is keeping the smoke largely out of the region.
The next round of widespread showers and thunderstorms for this area of the eastern Midwest and the East is forecast to arrive on Friday and continue through the weekend, which will clear the smoke.
But as long as the wildfires continue to rage in Canada, these events of dense smoke plumes will likely continue to disperse into the U.S. Canada's wildfire activity typically peaks from June to August.
Jun 28, 2023, 7:59 AM EDT
What to know about the Air Quality Index from wildfire smoke and how it affects human health
Heavy blankets of smoke billowing over the United States from wildfires burning in neighboring Canada are threatening the health of millions of people -- even non-vulnerable populations with no preexisting conditions. But what about the smoke makes it so hazardous for humans to be around?
Wildfire smoke contains fine particulate matter, known as PM2.5, which are microscopic solid or liquid droplets -- often 30 times smaller than the diameter of a human hair -- that can be inhaled and cause serious health problems, according to the U.S. Environmental Protection Agency.
Most particles form in the atmosphere as a result of complex reactions of chemicals, such as sulfur dioxide and nitrogen oxides -- pollutants emitted from power plants, industries and automobiles. But wildfires likely contain PM2.5 that is up to 10 times more harmful than the same type of air pollution coming from combustion activity, according to a 2021 study conducted in California.
Air Quality Index (AQI)
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PM2.5 is considered unhealthy for "Code Orange" and sensitive groups once the Air Quality Index surpasses 100, according to AirNow, a website that publishes air quality data. Once the AQI surpasses 150, it is considered "Code Red," unhealthy for some members of the general public who may experience health effects, with sensitive groups experiencing more severe effects.
The AQI is at "Code Purple" once it surpasses 200, considered "very unhealthy" with increased health risk for all populations. "Code Maroon" is labeled as "hazardous" and a health warning for emergency conditions once the AQI reaches 300 and higher.
At Code Maroon, "everyone is more likely to be affected," according to AirNow.
A "good" AQI is measured at 50 and below, and a "moderate" air quality index ranks between 51 and 100.
Chicago air quality hits 'very unhealthy' category
As Canadian wildfire smoke infiltrates the midwestern United States, the air in Chicago has deteriorated to the Air Quality Index's> "very unhealthy" category.
The AQI in hazy Chicago reached 250 on Tuesday afternoon. Any number over 100 is considered unhealthy for sensitive groups.
"We recommend children, teens, seniors, people with heart or lung disease, and individuals who are pregnant avoid strenuous activities and limit their time outdoors," Chicago Mayor Brandon Johnson warned in a statement. "For additional precautions, all Chicagoans may also consider wearing masks, limiting their outdoor exposure, moving activities indoors, running air purifiers, and closing windows."
Chicago's skyline is seen from the 360 Chicago Observation Deck of the John Hancock Building with heavy smoke from Canadian wildfires blanketing the city on June 27, 2023.
Kamil Krzaczynski/AFP via Getty Images
The smoke is forecast to clear on Friday when showers and thunderstorms hit the region.
Earlier this month, the AQI in the northeastern U.S. reached near maximum with levels in the high 400s.
Jun 28, 2023, 7:03 AM EDT
20 US states under air quality alerts
As of Wednesday morning, 20 U.S. states are under air quality alerts from Minnesota down to Georgia and as far north as western New York.
Wildfire smoke from neighboring Canada is currently blanketing large swaths of the United States, from Iowa to western Pennsylvania to North Carolina and most everywhere in between. Only Chicago is getting a small reprieve on Wednesday morning due to a lake breeze, which isn't expected to last for long.
Twenty U.S. states were under air quality alerts on the morning of June 28, 2023, due to smoke from wildfires in neighboring Canada.
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Later on Wednesday, the smoke is expected to cover areas from Minnesota to Washington, D.C. and down to the Carolinas.
Smoke from Canadian wildfires is forecast to blanket parts of the United States, from Minnesota to Washington D.C. and down to the Carolinas, on June 28, 2023.
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By early Thursday morning, the smoke will be seen in Minneapolis, Chicago, Indianapolis, Atlanta and Pittsburgh. But by the afternoon, it will linger from Detroit to Atlanta and east to Washington, D.C. and Philadelphia.
Smoke from Canadian wildfires will be seen in major U.S. cities like Minneapolis, Chicago, Indianapolis, Atlanta and Pittsburg on the morning of June 29, 2023.
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New York City could be impacted as well, but most of the smoke from the Canadian wildfires is expected to stay in western New York state, Pennsylvania and southern New Jersey.
Smoke from Canadian wildfires will linger from Detroit to Atlanta and east to Washington, D.C. and Philadelphia by the afternoon of June 29, 2023.
