Metro area air quality · 2025

Chicago-Naperville-Elgin, IL-IN-WI

Median AQI 54 (Moderate). 34.3% of monitored days rated Good across this metro's EPA monitoring network.

54
Median AQI
34.3%
Good-air days
6
Unhealthy days
3%
Cleaner than US metros

Aggregated from EPA Air Quality System (2025), 303 monitored days. EPA AQS →

The verdict

The Chicago-Naperville-Elgin, IL-IN-WI metro runs moderate on the EPA scale, among the more polluted US metros, a median AQI of 54 with 34.3% of 303 monitored days in the Good band.

54
median AQI · Moderate
34.3%
days rated Good
3%
cleaner than US metros
219
worst single reading

6 days reached Unhealthy or worse across the metro's monitors in 2025.

Insights: Chicago-Naperville-Elgin, IL-IN-WI metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 54 over 303 measured days in 2025, which corresponds to a Moderate band and a Poor metro-wide health grade. The monitored-day split lands at 104 Good days (34%), 170 Moderate (56%), and 23 Unhealthy-for-Sensitive-Groups (8%). The 90th-percentile AQI finished at 97 while the highest single-day reading hit 219 (Very Unhealthy). Metro residents averaged roughly 10.3 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by +42 and the median AQI moved -6 points, which classifies the multi-year trajectory as improving. The metro recorded 6 unhealthy-or-worse days combined, on those days the EPA recommends that sensitive groups limit prolonged outdoor exertion, and many schools and athletic programs adjust outdoor activity accordingly. Metros with comparable AQI profiles include Baton Rouge, LA (35.0% good, AQI 54); Bishop, CA (40.7% good, AQI 54); Cleveland-Elyria, OH (42.6% good, AQI 54).

Air Quality Summary

Median AQI

54

Moderate

Good Days

34.3%

104 of 303 days

Max AQI

219

Very Unhealthy

Health Grade

Poor

90th pct: 97

AQI Day Breakdown (2025)

Distribution of 303 monitored days across EPA AQI categories.

Good

104

34%

Moderate

170

56%

USG

23

8%

Unhealthy

5

2%

Very Unhealthy

1

0%

Hazardous

0

0%

Health Impact Assessment

Poor

The Chicago-Naperville-Elgin, IL-IN-WI metro area's air quality is rated Poor based on 34.3% good air days. There were 6 unhealthy days in 2025 when outdoor activity should be limited.

Air quality reached unhealthy levels on 6 days in 2025 (5 Unhealthy, 1 Very Unhealthy). Sensitive groups, including people with asthma, COPD, cardiovascular conditions, children, and adults over 65, should review the daily breakdown and follow local advisories.

Sensitive group advisory

People with asthma, COPD, heart disease, children, pregnant women, and adults 65+ should follow EPA AQI alerts daily and limit outdoor exertion when AQI exceeds 100. Real-time conditions: airnow.gov.

How does the Chicago-Naperville-Elgin, IL-IN-WI metro compare?

How Chicago-Naperville-Elgin, IL-IN-WI compares

Good-day share worse than US avg
Chicago-Naperville-Elgin, IL-IN-WI 34.3%
Baton Rouge, LA 35.0%
US average 71.3%
Median AQI worse than US avg
Chicago-Naperville-Elgin, IL-IN-WI 54
Baton Rouge, LA 54
US average 41
Unhealthy days / yr worse than US avg
Chicago-Naperville-Elgin, IL-IN-WI 6
Baton Rouge, LA 0
US average 1

5-Year Air Quality Trend

Air quality is improving in the Chicago-Naperville-Elgin, IL-IN-WI metro. Best year: 2025 (104 good days).

Year Good Moderate Unhealthy Median AQI
2020 62 280 5 60
2021 67 270 2 61
2022 93 257 2 56
2023 76 246 8 60
2024 95 254 2 56
2025 104 170 5 54

Metros with Similar Air Quality

Metro areas across the US with a similar median AQI to Chicago-Naperville-Elgin, IL-IN-WI.

Baton Rouge, LA

AQI 54 · 35.0% good

54

Bishop, CA

AQI 54 · 40.7% good

54

Cleveland-Elyria, OH

AQI 54 · 42.6% good

54

Columbus, OH

AQI 54 · 39.0% good

54

Fort Collins, CO

AQI 54 · 40.1% good

54

Fresno, CA

AQI 54 · 40.1% good

54

More Air Quality Data

Explore EPA air quality rankings and guides across U.S. metros and counties.

Cleanest Metro Areas

U.S. metros ranked by their share of Good air-quality days.

Worst Air Quality

Counties and metros with the most unhealthy air days.

All Metro Areas

Annual AQI by CBSA for every monitored U.S. metro area.

Best and Worst City Air

What drives urban air quality and how metro areas compare.

Air Quality Guides

Frequently Asked Questions

What is the air quality in the Chicago-Naperville-Elgin, IL-IN-WI metro area? ▼
The Chicago-Naperville-Elgin, IL-IN-WI metro area has a median Air Quality Index (AQI) of 54, rated "Moderate." 34.3% of monitored days (104 out of 303) had good air quality in 2025.
How many unhealthy air days does Chicago-Naperville-Elgin, IL-IN-WI have? ▼
In 2025, the Chicago-Naperville-Elgin, IL-IN-WI metro area recorded 6 unhealthy air days (5 Unhealthy, 1 Very Unhealthy, 0 Hazardous). The maximum AQI reached 219.
Is air quality in Chicago-Naperville-Elgin, IL-IN-WI getting better or worse? ▼
Air quality in the Chicago-Naperville-Elgin, IL-IN-WI metro is improving based on 5-year trends (2020-2025). Best year: 2025 with 104 good days. Worst year: 2020 with 62 good days.
What does AQI 54 mean for health? ▼
An AQI of 54 is "Moderate", air quality is acceptable, but some pollutants may pose a moderate health concern for a small number of sensitive individuals.
What is the 90th percentile AQI for Chicago-Naperville-Elgin, IL-IN-WI? ▼
The 90th percentile AQI for the Chicago-Naperville-Elgin, IL-IN-WI metro area is 97, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 219 (Very Unhealthy).
How does Chicago-Naperville-Elgin, IL-IN-WI compare to other metro areas? ▼
The Chicago-Naperville-Elgin, IL-IN-WI metro has 34.3% good air days. Similar metros: Baton Rouge, LA (35.0% good), Bishop, CA (40.7% good), Cleveland-Elyria, OH (42.6% good).

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset, 2020–2025. See our methodology for how AQI, median, and coverage figures are computed.

Read our methodology , how this data is sourced, computed, and verified.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by CBSA summary files (metro-level) · 2020–2025

Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.