The St. Louis metropolitan area is among the 25 cities ranked worst for ozone air pollution, according to the latest "State of the Air" report released by the health advocacy group the American Lung Association.
Ozone, a gas that occurs naturally in the upper atmosphere, is considered a pollutant at ground level. According to the report, the metropolitan area experienced an average of 10 high-ozone days each year between 2022 and 2024.
Ground-level ozone — the main component of smog — is created when pollution from cars, power plants and other sources interacts with the sun, which is why it's more common during hot months.
The number of high-ozone days in the U.S. has significantly decreased in the past 30 years, according to the report's authors.
High-ozone days can be particularly harmful for children, outdoor workers and people with asthma, said Laura Turner, advocacy director for Missouri at the American Lung Association.
She has asthma and said she can feel when the region is experiencing high-ozone days when she breathes:
"It's dangerous to breathe in. We compare it to a sunburn for your lungs. And ozone really impacts asthma, and you can see those really acute spikes in ozone translating to more asthma attacks, more health emergencies."
Greater St. Louis also ranked 31 for worst particle pollution out of the more than 200 cities studied. Particle pollution comes from sources such as coal plants, factories, vehicle exhaust and wildfire smoke. The ranking is actually an improvement from earlier years, when the region was ranked in the top 25 for the measure.
The 2026 "State of the Air" report emphasized air pollution's effects on young people. It pointed out that more than 40% of the nation's children live in an area with unhealthy levels of polluted air.
The report gave failing grades for ozone pollution to the city of St. Louis as well as St. Louis, Jefferson and St. Charles counties in Missouri and Jersey, Macoupin Madison and St. Clair counties in Illinois.
Climate change is causing more high-ozone days across the country, according to the report. Droughts, wildfires and rising temperatures all contribute to dirtier air.
"This report reflects both how far the St. Louis region has come and how much work still lies ahead," said Susannah Fuchs, director of healthy air solutions at the organization's Missouri chapter, in a news release. "Recent environmental and climate-related pressures are putting those gains at risk."
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