Chicago Air Quality in Summer
Across 2019–2025, Chicago's summer (June–August) air quality had a median AQI of 69 (Moderate) over 644 monitored days in the Chicago-Naperville-Elgin, IL-IN-WI area. 20.7% of summer days (133 of 644) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 50.6% of days. The cleanest summer on record here was 2022 (median AQI 62, 11 days above 100) and the worst was 2023 (median 80, 33 days above 100, peak AQI 246).
- Good: 11.0%
- Moderate: 68.3%
- Unhealthy for Sensitive Groups: 16.8%
- Unhealthy or worse: 3.9%
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How is the air in Chicago in summer?
Moderate on a typical day: median AQI 69 across 2019–2025, with 20.7% of summer days above AQI 100. Ground-level ozone is the main driver.
- ✓11.0% of summer days were Good (AQI 0–50), 68.3% Moderate (51–100).
- ✓133 days of 644 reached AQI 101+; the summer peak was 246.
- ✓Cleanest month: August; worst month: June.
Frequently asked questions
What is the air quality like in Chicago in summer?▾
Across 2019–2025, the median daily AQI in Chicago in summer was 69 (Moderate). 11.0% of days were Good, 68.3% Moderate, and 20.7% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is summer a good time for outdoor exercise in Chicago?▾
A typical summer day in Chicago is Moderate (median AQI 69): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 5 of summer days (20.7%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Chicago's summer air quality problems?▾
Ground-level ozone set the daily AQI on 50.6% of summer days in Chicago. The highest summer AQI recorded in 2019–2025 was 246 (Very Unhealthy), in 2023.
Chicago summer air quality, year by year
Chicago summer air quality by year (Chicago-Naperville-Elgin, IL-IN-WI, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 92 | 67 | 13 | 174 | PM2.5 |
| 2020 | 92 | 74 | 22 | 197 | O3 |
| 2021 | 92 | 71 | 19 | 156 | O3 |
| 2022cleanest | 92 | 62 | 11 | 164 | O3 |
| 2023worst | 92 | 80 | 33 | 246 | O3 |
| 2024 | 92 | 66 | 11 | 166 | O3 |
| 2025 | 92 | 73 | 24 | 168 | O3 |
What summer air means in Chicago
A typical summer day in Chicago is Moderate (median AQI 69): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 5 of summer days (20.7%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Summer's median AQI of 69 is above Chicago's whole-year median of 60, making it one of the area's dirtier periods. Nationally, the median Summer AQI across every EPA metro area (308,645 metro-days, 2019–2025) is 46, so Chicago runs above the national Summer norm; 20.7% of its Summer days topped AQI 100 versus 3.6% nationally (above average).
Within the season, August is the cleanest month (median AQI 62, 13.3% of days above 100) and June the worst (median 77, 25.2% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Chicago
The latest EPA AirNow observation puts Chicago's AQI at 46 (PM2.5). The figures above are multi-year season statistics, not today's reading.
View current Chicago air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Chicago-Naperville-Elgin, IL-IN-WI), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.