Chicago air quality ranked among worst in US, but why is it so bad?

Chicago’s air quality is among the worst in the U.S. according to a new ranking, but what’s driving the increase in pollution?

According to the 2025 State of the Air Report, released by the American Lung Association on Wednesday, the Chicago-Naperville metropolitan area is one of the most polluted in the U.S. in terms of both ozone and year-round particle pollution.

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The metro area rose from 17^th in the country in ozone pollution to 15^th, and is now 13^th in the country in terms of year-round particle pollution, the ALA said in their annual report.

Los Angeles tops the list of cities most impacted by ozone pollution, followed by Visalia, California and Bakersfield, California. Phoenix is fourth, and Fresno, California round out the top-five.

In fact, seven of the top-14 most polluted cities in terms of ozone are in California.

The number of high ozone days in Chicago reached its highest level since the 2011-13 analysis, according to officials.

But what is leading to the concerns about air quality in Chicago?

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According to the American Lung Association, man-made pollution has still been seeing decreases, with the transportation sector, power plants and manufacturing all seeing reductions in the amount of pollutants they emit.

What’s been leading to increases has been wildfire smoke, which has blanketed large swaths of the country on numerous occasions, according to the research.

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Those wildfires are growing in intensity and scope because of extreme heat and drought, the ALA said, and as a result particle pollution has become a more significant issue in the United States.

That extreme heat is also causing increased use of air conditioning, which also increases the amount of pollutants in the air.

Nearly half of the U.S. population lives in areas with unhealthy amounts of air pollution.

The ALA says there are nearly 500,000 individuals with COPD living in the area, along with more than 600,000 who have been diagnosed with a cardiovascular disease and nearly 900,000 individuals with asthma, three of the groups most at-risk for ill effects from poor air quality.