Median AQI
46
Good
California · County air quality · 2025
Plumas County, California
Median AQI 46 (Good). 52.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 46
- Median AQI
- 52.8%
- Good-air days
- 0
- Unhealthy days
- 8%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Plumas County's air is good on balance, among the most polluted counties nationally, a median AQI of 46 with 52.8% of 195 monitored days in the Good band, driven mainly by PM2.5.
- 46
- median AQI · Good
- 52.8%
- days rated Good
- PM2.5
- main pollutant
- 8%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 111.
Data updated July 2026
- Good · 103 d · 52.8%
- Moderate · 88 d · 45.1%
- USG · 4 d · 2.1%
How did Plumas County's air break down in 2025?
Across 195 monitored days, 103 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 111 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 195 days monitored. Median AQI: 46 (Good).
Insights: Plumas County, California. EPA monitors recorded a median Air Quality Index of 46 across 195 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 103 (53%) fell in the Good band (AQI 0–50), 88 (45%) registered Moderate readings, and 4 (2%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 82, while the worst single-day peak hit 111 (USG). Residents averaged about 15.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (195 days). Across the 2020–2025 trend window, good days shifted by -32 and the median AQI moved -10 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 111, usg but never Unhealthy. Nearby counties show comparable readings: Amador (84.8% good, AQI 40); Butte (66.1% good, AQI 47); 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).
Air Quality Summary
Good Days
52.8%
103 of 195 monitored days
-22.2pp vs 75% target
Max AQI Recorded
111
USG
Health Grade
Moderate
90th-pct AQI 82
Plumas County, Good days share 52.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Plumas 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 195 monitored days across EPA AQI categories.
Good
103
53%
Moderate
88
45%
USG
4
2%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Plumas County.
- PM2.5 · 195 days · 100.0%
Health Impact Assessment
Moderate
Plumas County's air quality is rated Moderate based on 52.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 52.8% of monitored days in 2025, with a median AQI of 46. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 195 of 195 monitored days.
5-Year Air Quality Trend
Air quality is improving in Plumas County. Best year: 2024 (188 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 135 | 175 | 16 | 17 | 56 | 755 |
| 2021 | 97 | 184 | 37 | 24 | 67 | 654 |
| 2022 | 148 | 182 | 25 | 4 | 55 | 175 |
| 2023 | 186 | 168 | 11 | 0 | 50 | 142 |
| 2024 | 188 | 162 | 7 | 7 | 48 | 253 |
| 2025 | 103 | 88 | 4 | 0 | 46 | 111 |
How does Plumas County compare?
How Plumas County compares
Good-day share worse than US avg
Plumas County 52.8%
Amador County, California 84.8%
US average 76.5%
Median AQI worse than US avg
Plumas County 46
Amador County, California 40
US average 38
Unhealthy days / yr about average
Plumas 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 Plumas County.
Bay County, Florida
AQI 46 · 60.6% good
Blount County, Tennessee
AQI 46 · 69.6% good
Cache County, Utah
AQI 46 · 61.2% good
Chesterfield County, South Carolina
AQI 46 · 61.2% good
Clark County, Indiana
AQI 46 · 59.7% good
Clark County, Ohio
AQI 46 · 59.4% good
What Plumas County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 46 means for exposure. Health guidance
- See how Plumas County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Plumas County with its California neighbours before drawing a conclusion about the region. All of California
Based on 195 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 Plumas County, California? ▼
Plumas County has a median Air Quality Index (AQI) of 46, rated "Good." 52.8% of monitored days (103 out of 195) had good air quality in 2025.
What is the main pollutant in Plumas County? ▼
The primary pollutant in Plumas County is Fine Particles (PM2.5), which was the main AQI driver on 195 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Plumas County have? ▼
In 2025, Plumas County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 111.
Is the air quality in Plumas County getting better or worse? ▼
Air quality in Plumas County is improving based on 5-year trends (2020-2025). Best year: 2024 with 188 good days. Worst year: 2021 with 97 good days.
What does AQI 46 mean for health? ▼
Plumas County's median AQI of 46 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 Plumas County compare to other counties in California? ▼
Plumas County has 52.8% good air days. Nearby counties in California: Amador (84.8% good), Butte (66.1% good), Calaveras (73.9% good), Colusa (84.9% good), Del Norte (81.0% good), El Dorado (85.8% good).
What is the 90th percentile AQI in Plumas County? ▼
The 90th percentile AQI for Plumas County is 82, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 111 (USG).
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.