Chicago Air Quality in October
Across 2019–2025, Chicago's October air quality had a median AQI of 55 (Moderate) over 217 monitored days in the Chicago-Naperville-Elgin, IL-IN-WI area. 1.8% of October days (4 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 73.7% of days. The cleanest October on record here was 2019 (median AQI 55, 0 days above 100) and the worst was 2021 (median 55, 2 days above 100, peak AQI 114).
- Good: 30.4%
- Moderate: 67.7%
- Unhealthy for Sensitive Groups: 1.8%
- Unhealthy or worse: 0.0%
Improve Indoor Air Quality
Even with good outdoor air in Chicago, indoor PM2.5, dust and allergens build up. A True-HEPA purifier keeps a bedroom or office consistently clean.
Recommended: Levoit Core 400S — True HEPA · CADR ~141 CFM · rooms up to 219 sq ft
As an Amazon Associate, we earn from qualifying purchases.
How is the air in Chicago in October?
Moderate on a typical day: median AQI 55 across 2019–2025, with 1.8% of October days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓30.4% of October days were Good (AQI 0–50), 67.7% Moderate (51–100).
- ✓4 days of 217 reached AQI 101+; the October peak was 122.
- ✓Best October: 2019; worst October: 2021.
Frequently asked questions
What is the air quality like in Chicago in October?▾
Across 2019–2025, the median daily AQI in Chicago in October was 55 (Moderate). 30.4% of days were Good, 67.7% Moderate, and 1.8% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in Chicago?▾
A typical October day in Chicago is Moderate (median AQI 55): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 56 of October days (1.8%) 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 October air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 73.7% of October days in Chicago. The highest October AQI recorded in 2019–2025 was 122 (Unhealthy for Sensitive Groups), in 2021.
Chicago October air quality, year by year
Chicago October 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 |
|---|---|---|---|---|---|
| 2019cleanest | 31 | 55 | 0 | 73 | PM2.5 |
| 2020 | 31 | 56 | 0 | 75 | PM2.5 |
| 2021worst | 31 | 55 | 2 | 114 | PM2.5 |
| 2022 | 31 | 56 | 0 | 96 | PM2.5 |
| 2023 | 31 | 55 | 1 | 101 | PM2.5 |
| 2024 | 31 | 59 | 0 | 92 | PM2.5 |
| 2025 | 31 | 47 | 1 | 122 | PM2.5 |
What October air means in Chicago
A typical October day in Chicago is Moderate (median AQI 55): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 56 of October days (1.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
October's median AQI of 55 is below Chicago's whole-year median of 60, making it one of the area's cleaner periods. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so Chicago runs above the national October norm; 1.8% of its October days topped AQI 100 versus 1.3% nationally (about the same).
October is part of Chicago's fall season (September, October, November); the fall page pools all three months.
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 month 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.