New Report Ranks Chicago 2nd Worst for Air Quality in U.S.

A new report identified Chicago’s air quality as the second worst of any major city in the U.S. last year.

Chicago’s air quality was the second worst of any major city in the U.S. last year, according to the 2023 IQAir World Air Quality Report, released March 19.

Chicago’s average PM2.5 concentration was 13 micrograms per cubic meter, just behind the top most polluted American city — Columbus, Ohio — which had an average concentration of 13.9 micrograms per cubic meter of PM2.5 concentration, according to the report. Chicago suffered its worst air quality during the summer months of June through August with a peak concentration of 28.4 micrograms per cubic meter in June largely due to Canadian wildfires.

PM2.5 refers to particles smaller than 2.5 micrograms, which are a type of pollution small enough to enter the lungs, according to Loyola environmental science and sustainability master’s student Nora Hartnett.

Hartnett said any solids or liquids in the air below this size threshold are considered particulate matter and can drastically affect health once inside the bloodstream or lungs, which is why this level of dangerous pollutant is often specifically monitored. PM2.5 exposure has been linked to aggravated asthma, nonfatal heart attacks or decreased lung function among other heart and lung problems, according to the Environmental Protection Agency.

The World Air Quality Report is the sixth annual report from Swiss air filter company IQAir, which sells air purifiers and face masks among other products, according to their website

The report is based on data from ground-level air quality monitoring stations operated by governments, non-profit community organizations, educational institutions and individuals around the world, according to the report’s methodology.

The report said average air quality across the U.S. slightly declined in 2023, with the Midwest and mid-Atlantic regions suffering the largest increases because of smoke from Canadian wildfires.

Hundreds of fires burned last summer in possibly Canada’s worst wildfire season yet, causing massive amounts of smoke to drift over large swaths of the U.S. in a thick haze, the Associated Press reported.

Much of the West Coast’s air quality improved over 2023 because of a mild wildfire season there, according to the report. The report also said out of the 25 most populated cities, Las Vegas was the least polluted with an average PM2.5 concentration of 4.9 micrograms per cubic meter.

Hartnett said average air quality in Chicago and the country in general has been improving primarily thanks to environmental regulation like the Clean Air Act, a landmark federal environmental law that created emissions regulations and national standards for air pollution, according to the EPA.

However, Hartnett said intense spikes of high air pollution from wildfire smoke are much harder to control and can also affect overall levels if they’re powerful, like they were last summer.

“The wildfires we saw last summer in Canada were just so drastic, I wouldn’t be surprised if that was kind of an extreme event,” Hartnett said. “But I do think there will be a trend of worsening air quality that we are going to consistently see. I think wildfires are going to get bigger, they’re going to last longer and we’re gonna see that continue.”

The Chicago metro area was ranked 23rd worst for annual particle pollution out of a list of 200 metropolitan areas across the country and 77th worst for 24-hour particle pollution out of a similar list of 223 areas by the American Lung Association for 2023. The most recent available Illinois Air Quality Report from the state’s Environmental Protection Agency is for 2021, which detailed a steady decrease in annual levels of PM2.5.

Associate professor of chemistry Dr. Martina Schmelling said she would be careful when looking at data and rankings from non-governmental agencies like IQAir because lots of factors can contribute to overall air quality and government agencies have very clear mechanisms for validating their data, which she said is why their reports aren’t done yet.

Hartnett said she was surprised at how high Chicago ranked in the IQAir report. Despite the inevitable air pollution issues that come with larger industrial areas like Chicago, Hartnett said the city has good air quality regulations. Schmelling said while it’s not possible to remove all pollution from the industrial center of Chicago, the general trend over the last 20 years has been a decrease in pollutants.

Loyola students have been monitoring air quality across Chicago in the Community Air Quality Research Experience co-created by Associate Professor Dr. Ping Jing and Assistant Professor Dr. Tania Schusler from the School of Environmental Sustainability, The Phoenix previously reported.

The Community Air Quality Research Experience project uses low-cost Purple Air sensors which are less accurate than the expensive government air-quality sensors but can be placed more often, according to Schusler.

“Initially, we’re looking more at what’s happening in terms of proximity to major roadways, in terms of proximity to the industrial facilities,” Schusler said. “And now it’s thinking about that other source, pollution source that’s outside of our region.”

While keeping an eye to outside sources, Jing wrote in an email to The Phoenix they must continue to monitor local sources of particulate matter as well.

“The fact that Chicago’s air quality was the 2nd worst in the nation last year could have been significantly influenced by the smoke from upwind wildfires,” Jing wrote. “But it does not mean we can ignore the pollution we produce right here in our city, which might have also got worse last year. I would need to investigate it more to be sure.”

Local air quality levels are viewable at or

Featured image by Leslie Meraz / The Phoenix

Hunter Minné

Hunter Minné