Metro area air quality · 2025

Chico, CA

Median AQI 47 (Good). 66.1% of monitored days rated Good across this metro's EPA monitoring network.

47
Median AQI
66.1%
Good-air days
0
Unhealthy days
36%
Cleaner than US metros

Aggregated from EPA Air Quality System (2025), 245 monitored days. EPA AQS →

The verdict

The Chico, CA metro runs good on the EPA scale, more polluted than the median US metro, a median AQI of 47 with 66.1% of 245 monitored days in the Good band.

47
median AQI · Good
66.1%
days rated Good
36%
cleaner than US metros
96
worst single reading

No day crossed into the Unhealthy tier across the metro's monitors in 2025.

Insights: Chico, CA metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 47 over 245 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 162 Good days (66%), 83 Moderate (34%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 59 while the highest single-day reading hit 96 (Moderate). Metro residents averaged roughly 19.8 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by +13 and the median AQI moved -7 points, which classifies the multi-year trajectory as improving. The metro avoided any Unhealthy-tier days entirely, an outcome that typically reflects favorable wind patterns, lower industrial density, or effective regional emission controls. Metros with comparable AQI profiles include Ardmore, OK (65.3% good, AQI 47); Baltimore-Columbia-Towson, MD (62.2% good, AQI 47); Boise City, ID (64.7% good, AQI 47).

Air Quality Summary

Median AQI

47

Good

Good Days

66.1%

162 of 245 days

Max AQI

96

Moderate

Health Grade

Moderate

90th pct: 59

AQI Day Breakdown (2025)

Distribution of 245 monitored days across EPA AQI categories.

Good

162

66%

Moderate

83

34%

USG

0

0%

Unhealthy

0

0%

Very Unhealthy

0

0%

Hazardous

0

0%

Health Impact Assessment

Moderate

The Chico, CA metro area's air quality is rated Moderate based on 66.1% good air days. No unhealthy air days were recorded in 2025.

Air quality is generally acceptable. Unusually sensitive people should monitor real-time conditions at AirNow.gov during high-pollution events.

How does the Chico, CA metro compare?

How Chico, CA compares

Good-day share worse than US avg
Chico, CA 66.1%
Ardmore, OK 65.3%
US average 71.3%
Median AQI worse than US avg
Chico, CA 47
Ardmore, OK 47
US average 41
Unhealthy days / yr better than US avg
Chico, CA 0
Ardmore, OK 2
US average 1

5-Year Air Quality Trend

Air quality is improving in the Chico, CA metro. Best year: 2024 (231 good days).

Year Good Moderate Unhealthy Median AQI
2020 149 178 16 54
2021 160 174 10 53
2022 191 171 0 50
2023 191 174 0 50
2024 231 133 1 46
2025 162 83 0 47

Metros with Similar Air Quality

Metro areas across the US with a similar median AQI to Chico, CA.

Ardmore, OK

AQI 47 · 65.3% good

47

Baltimore-Columbia-Towson, MD

AQI 47 · 62.2% good

47

Boise City, ID

AQI 47 · 64.7% good

47

Cheyenne, WY

AQI 47 · 69.8% good

47

Columbus, GA-AL

AQI 47 · 58.8% good

47

Fort Wayne, IN

AQI 47 · 55.7% good

47

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 Chico, CA metro area? ▼
The Chico, CA metro area has a median Air Quality Index (AQI) of 47, rated "Good." 66.1% of monitored days (162 out of 245) had good air quality in 2025.
How many unhealthy air days does Chico, CA have? ▼
In 2025, the Chico, CA metro area recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 96.
Is air quality in Chico, CA getting better or worse? ▼
Air quality in the Chico, CA metro is improving based on 5-year trends (2020-2025). Best year: 2024 with 231 good days. Worst year: 2020 with 149 good days.
What does AQI 47 mean for health? ▼
An AQI of 47 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
What is the 90th percentile AQI for Chico, CA? ▼
The 90th percentile AQI for the Chico, CA metro area is 59, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 96 (Moderate).
How does Chico, CA compare to other metro areas? ▼
The Chico, CA metro has 66.1% good air days. Similar metros: Ardmore, OK (65.3% good), Baltimore-Columbia-Towson, MD (62.2% good), Boise City, ID (64.7% 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.