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, 10:33 AM EDT
How to stay safe from wildfire smoke amid reduced air quality
Wildfire smoke and ash can irritate eyes, nose, throat and lungs, making you cough or wheeze and can make it hard to breathe, according to the U.S. Centers for Disease Control and Prevention.
The CDC says the most effective way to protect yourself during wildfire emergencies is to stay indoors or limit time outdoors when there is smoke in the air. This is especially important for those with heart or lung conditions who are at higher risk for adverse health effects.
"People who are most at risk are [the] elderly, immunocompromised, young children and people who already have respiratory problems, people with asthma and things like that," said Dr. Stephanie Widmer, a member of ABC News' Medical Unit.
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)
ABC News Photo Illustration
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.
