A smokey view of Downtown Chicago while air quality remains at unhealthy levels on June 28, 2023. Credit: Colin Boyle/Block Club Chicago

CHICAGO — For much of Tuesday, Chicago had the worst air quality of any big city in the world — and it has not improved much as of Wednesday morning.

According to AirNow, the official U.S. Air Quality Index, the city’s air quality was “Very Unhealthy” as of 8:30 a.m. Another air quality monitoring system, IQAir, listed the city as the third worst in the world Wednesday, behind Detroit and the United Arab Emirates.

The National Weather Service blamed the conditions and low visibility on the wildfire smoke that has traveled down from Canada and impacted large regions of the United States. The service suggested limiting prolonged outdoor activities.

Credit: Colin Boyle/Block Club Chicago

Argonne National Laboratory atmospheric scientist Scott Collis said wildfire smoke has also been trapped in the Chicago area by what’s known as an atmospheric inversion, where temperatures increase in the atmosphere.

“What that does is, it puts a cap on the atmosphere. It means that it makes it very difficult for smoke to rise, so a lot of that wildfire smoke got trapped under that inversion that actually caused this,” Collis said. “If I look out my window right now, you’d swear that it was overcast, but there are actually no clouds above us right now. That’s all smoke.”

Haze from Canadian wildfire smoke obscures the view of the Chicago skyline from Montrose Beach on June 27, 2023. Credit: Colin Boyle/Block Club Chicago

Collis said Chicago was likely to reach its peak of the air quality readings Tuesday, with gradual improvement Wednesday.

But as long as wildfires keep burning in Ontario and Quebec, Chicago will likely be hit with smoky skies again, he said.

“The real question is, how long until we get our next storm system that comes through that brings the winds back around from Canada?” he said. “So long term, what we need is for those wildfires to go away, because this is just going to keep happening in a cyclical fashion as we start to get our winds from the north and northwest again.”

According to AirNow’s forecast, Chicago should move from “Very Unhealthy” air quality Wednesday to “Unhealthy for Sensitive Groups” on Thursday, a slight improvement. By the weekend, the air quality should return to “moderate,” according to the index.

Chicago Public Schools said in an email to families Tuesday it would move its summer programs indoors “to reduce the risk to students and staff.”

Mayor Brandon Johnson also issued a statement saying the city is monitoring the situation and urging children, teens, seniors, people with heart or lung disease and  pregnant people to avoid strenuous activities and limit time outdoors.

“For additional precautions, all Chicagoans may also consider wearing masks, limiting their outdoor exposure, moving activities indoors, running air purifiers and closing windows,” the statement reads. “As these unsafe conditions continue, the City will continue to provide updates and take swift action to ensure that vulnerable individuals have the resources they need to protect themselves and their families. Anyone who needs immediate medical attention should dial 911.”

Residents can check airnow.gov to keep track of the air quality throughout the day.

Some city buildings are available at various hours for Chicagoans who need to shelter in places with better ventilation, Johnson said. People can visit any Chicago public library, senior center or the Chicago Cultural Center, 78 E. Washington St.

Find your local library hereFind your nearest senior center here.

People also can visit six community service centers. All operate 9 a.m.-5 p.m. Monday-Friday, except for the Garfield Center, which is open 24 hours.

  • Englewood Center, 1140 W. 79th St.
  • Garfield Center, 10 S. Kedzie Ave. (24 Hours)
  • King Center, 4314 S. Cottage Grove Ave.
  • North Area Center, 845 W. Wilson Ave.
  • South Chicago Center, 8650 S. Commercial Ave.
  • Trina Davila Center, 4312 W. North Ave.

The American Lung Association and Mount Sinai Health System shared the following tips for those looking to limit exposure to unhealthy air:

  • Avoid exercising outdoors and stay inside with windows closed and air conditioning on if possible.
  • Avoid driving your car if possible, as auto use contributes to poor air quality.
  • Don’t smoke.
  • If you must be outside, consider wearing an N95 or KN95 mask. Surgical masks will not be helpful with air pollution, according to Mount Sinai Health.

Dr. Ravi Kalhan, a pulmonologist at Northwestern Medicine, agreed people should avoid outdoor exercise and other activities when the air quality is so poor. He said those with asthma should “absolutely” wear a KN95 mask outside, if possible.

“An AQI of 20, if you were outside all day, is very close to smoking one cigarette a day. So an AQI of 200-ish, if you spent the whole day outside, is equivalent to smoking 10 cigarettes,” he said.

Chicago’s Air Quality Index was 215 at 8:30 a.m. Wednesday.

Kalhan said on top of keeping windows closed, people can also keep their HVAC system running — if it has a high quality filter — to clean the air in their homes.

“If they have a central HVAC system with a central filter, and that filter is a high quality filter in the range of MERV eight to 13, it’s probably best to run the HVAC fan, so the air gets cleaned continuously with the windows closed,” he said. “If people don’t have central air and can afford a portable air purifier with a HEPA filter, running that indoors with the windows closed is best practice.”

While the bad air quality is harmful to vulnerable populations, a single-day event should be manageable for most people, Kalhan said. But the long term ramifications are more concerning, and could lead to “a big public health problem,” he said.

“Kids can’t stay inside every day, right? That’s not a possibility. And if our youth are continuously exposed to the equivalent of five to 10 cigarettes a day from the day they’re born till the day they’re 40, there’s a chronic health risk associated with that,” he said. “We need to confront it in the big picture through that lens, that the more often we have these days, the greater the threat there is to the long term public health.” 

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