SmogRank / World / United States / Illinois / September 2023
Most polluted cities in Illinois, United States, September 2023
21 cities in Illinois, United States ranked by their average PM2.5 over the 30 days. Worst: East Saint Louis at 13.1 µg/m³, #237 of 2,128 cities in the world. Cleanest: Winthrop Harbor at 6.7. A city needs measurements on 70% of the days to be ranked.
About 0 people in this city breathed unhealthy air on an average day of September 2023.
Ranked by people: each city's population times its share of unhealthy days, those with a daily mean over 35.4 µg/m³ (US AQI 101+). That is how many people living there breathed unhealthy air on an average day. Only cities measured at 2 or more places at least 3 km apart are ranked: one monitor shouldn't speak for a whole city. Population is the city itself, not its wider metro area.
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The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
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SmogRank, most polluted cities in Illinois, United States, PM2.5, September 2023, smogrank.com/us/region/illinois/history/2023-09 (accessed 6 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.