Median AQI
47
Good
California · County air quality · 2025
Butte County, California
Median AQI 47 (Good). 66.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 47
- Median AQI
- 66.1%
- Good-air days
- 0
- Unhealthy days
- 25%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Butte County's air is good on balance, more polluted than the median US county, a median AQI of 47 with 66.1% of 245 monitored days in the Good band, driven mainly by Ozone.
- 47
- median AQI · Good
- 66.1%
- days rated Good
- Ozone
- main pollutant
- 25%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 96.
Data updated July 2026
- Good · 162 d · 66.1%
- Moderate · 83 d · 33.9%
How did Butte County's air break down in 2025?
Across 245 monitored days, 162 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 96 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 245 days monitored. Median AQI: 47 (Good).
Insights: Butte County, California. EPA monitors recorded a median Air Quality Index of 47 across 245 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 162 (66%) fell in the Good band (AQI 0–50), 83 (34%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 59, while the worst single-day peak hit 96 (Moderate). Residents averaged about 19.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (139 days), PM2.5 (106 days). Across the 2020–2025 trend window, good days shifted by +13 and the median AQI moved -7 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 96, moderate but never Unhealthy. Nearby counties show comparable readings: Amador (84.8% good, AQI 40); Calaveras (73.9% good, AQI 43); Colusa (84.9% good, AQI 39); Del Norte (81.0% good, AQI 33); El Dorado (85.8% good, AQI 39); Fresno (40.1% good, AQI 54).
Air Quality Summary
Good Days
66.1%
162 of 245 monitored days
-8.9pp vs 75% target
Max AQI Recorded
96
Moderate
Health Grade
Moderate
90th-pct AQI 59
Butte County, Good days share 66.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Butte County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
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%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Butte County.
- Ozone · 139 days · 56.7%
- PM2.5 · 106 days · 43.3%
Health Impact Assessment
Moderate
Butte County's air quality is rated Moderate based on 66.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 66.1% of monitored days in 2025, with a median AQI of 47. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 139 of 245 monitored days.
5-Year Air Quality Trend
Air quality is improving in Butte County. Best year: 2024 (231 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 149 | 178 | 18 | 16 | 54 | 508 |
| 2021 | 160 | 174 | 18 | 10 | 53 | 257 |
| 2022 | 191 | 171 | 3 | 0 | 50 | 119 |
| 2023 | 191 | 174 | 0 | 0 | 50 | 100 |
| 2024 | 231 | 133 | 0 | 1 | 46 | 213 |
| 2025 | 162 | 83 | 0 | 0 | 47 | 96 |
How does Butte County compare?
How Butte County compares
Good-day share worse than US avg
Butte County 66.1%
Amador County, California 84.8%
US average 76.5%
Median AQI worse than US avg
Butte County 47
Amador County, California 40
US average 38
Unhealthy days / yr about average
Butte County 0
Amador County, California 0
US average 0
Other Counties in California
Air quality comparison for nearby counties in California.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Butte County.
Beaver County, Pennsylvania
AQI 47 · 54.3% good
Bell County, Texas
AQI 47 · 61.3% good
Bowie County, Texas
AQI 47 · 57.3% good
Bronx County, New York
AQI 47 · 56.6% good
Calcasieu County, Louisiana
AQI 47 · 61.5% good
Carbon County, Utah
AQI 47 · 62.9% good
What Butte County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 47 means for exposure. Health guidance
- See how Butte County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Butte County with its California neighbours before drawing a conclusion about the region. All of California
Based on 245 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Butte County, California? ▼
Butte County 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.
What is the main pollutant in Butte County? ▼
The primary pollutant in Butte County is Ozone (O3), which was the main AQI driver on 139 days (57% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Butte County have? ▼
In 2025, Butte County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 96.
Is the air quality in Butte County getting better or worse? ▼
Air quality in Butte County 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? ▼
Butte County's median AQI of 47 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Butte County compare to other counties in California? ▼
Butte County has 66.1% good air days. Nearby counties in California: Amador (84.8% good), Calaveras (73.9% good), Colusa (84.9% good), Del Norte (81.0% good), El Dorado (85.8% good), Fresno (40.1% good).
What is the 90th percentile AQI in Butte County? ▼
The 90th percentile AQI for Butte County is 59, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 96 (Moderate).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
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.