Chicago Air Quality in Winter
Across 2019–2025, Chicago's winter (December–February) air quality had a median AQI of 58 (Moderate) over 632 monitored days in the Chicago-Naperville-Elgin, IL-IN-WI area. 0.8% of winter days (5 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 93.5% of days. The cleanest winter on record here was 2025 (median AQI 55, 0 days above 100) and the worst was 2021 (median 61, 2 days above 100, peak AQI 104).
- Good: 19.5%
- Moderate: 79.7%
- Unhealthy for Sensitive Groups: 0.8%
- Unhealthy or worse: 0.0%
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How is the air in Chicago in winter?
Moderate on a typical day: median AQI 58 across 2019–2025, with 0.8% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓19.5% of winter days were Good (AQI 0–50), 79.7% Moderate (51–100).
- ✓5 days of 632 reached AQI 101+; the winter peak was 125.
- ✓Cleanest month: January; worst month: December.
Frequently asked questions
What is the air quality like in Chicago in winter?▾
Across 2019–2025, the median daily AQI in Chicago in winter was 58 (Moderate). 19.5% of days were Good, 79.7% Moderate, and 0.8% reached Unhealthy for Sensitive Groups or worse, based on 632 monitored days in EPA's Air Quality System.
Is winter a good time for outdoor exercise in Chicago?▾
A typical winter day in Chicago is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of winter days 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 winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 93.5% of winter days in Chicago. The highest winter AQI recorded in 2019–2025 was 125 (Unhealthy for Sensitive Groups), in 2021.
Chicago winter air quality, year by year
Chicago winter 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 | 90 | 59 | 0 | 91 | PM2.5 |
| 2020 | 91 | 60 | 1 | 103 | PM2.5 |
| 2021worst | 90 | 61 | 2 | 104 | PM2.5 |
| 2022 | 90 | 57 | 0 | 96 | PM2.5 |
| 2023 | 90 | 56 | 1 | 125 | PM2.5 |
| 2024 | 91 | 56 | 1 | 111 | PM2.5 |
| 2025cleanest | 90 | 55 | 0 | 79 | PM2.5 |
What winter air means in Chicago
A typical winter day in Chicago is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of winter days reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Winter's median AQI of 58 is in line with Chicago's whole-year median of 60, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so Chicago runs above the national Winter norm; 0.8% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, January is the cleanest month (median AQI 57, 0.0% of days above 100) and December the worst (median 59, 1.4% 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.