Median AQI
45
Good
California · County air quality · 2025
Mariposa County, California
Median AQI 45 (Good). 81.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 45
- Median AQI
- 81.6%
- Good-air days
- 0
- Unhealthy days
- 57%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Mariposa County's air is good on balance, cleaner than the median US county, a median AQI of 45 with 81.6% of 250 monitored days in the Good band, driven mainly by Ozone.
- 45
- median AQI · Good
- 81.6%
- days rated Good
- Ozone
- main pollutant
- 57%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 90.
Data updated July 2026
- Good · 204 d · 81.6%
- Moderate · 46 d · 18.4%
How did Mariposa County's air break down in 2025?
Across 250 monitored days, 204 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 90 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 250 days monitored. Median AQI: 45 (Good).
Insights: Mariposa County, California. EPA monitors recorded a median Air Quality Index of 45 across 250 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 204 (82%) fell in the Good band (AQI 0–50), 46 (18%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 90 (Moderate). Residents averaged about 24.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (249 days), PM2.5 (1 days). Across the 2020–2025 trend window, good days shifted by +9 and the median AQI moved -4 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 90, moderate 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
81.6%
204 of 250 monitored days
6.6pp vs 75% target
Max AQI Recorded
90
Moderate
Health Grade
Good
90th-pct AQI 61
Mariposa County, Good days share 81.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Mariposa 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 250 monitored days across EPA AQI categories.
Good
204
82%
Moderate
46
18%
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 Mariposa County.
- Ozone · 249 days · 99.6%
- PM2.5 · 1 days · 0.4%
Health Impact Assessment
Good
Mariposa County's air quality is rated Good based on 81.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 81.6% of monitored days in 2025, with a median AQI of 45. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 249 of 250 monitored days.
5-Year Air Quality Trend
Air quality is improving in Mariposa County. Best year: 2024 (255 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 195 | 123 | 27 | 10 | 49 | 1073 |
| 2021 | 193 | 140 | 25 | 7 | 49 | 162 |
| 2022 | 211 | 125 | 8 | 21 | 48 | 198 |
| 2023 | 217 | 131 | 10 | 5 | 47 | 264 |
| 2024 | 255 | 105 | 6 | 0 | 45 | 133 |
| 2025 | 204 | 46 | 0 | 0 | 45 | 90 |
How does Mariposa County compare?
How Mariposa County compares
Good-day share better than US avg
Mariposa County 81.6%
Amador County, California 84.8%
US average 76.5%
Median AQI worse than US avg
Mariposa County 45
Amador County, California 40
US average 38
Unhealthy days / yr about average
Mariposa 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 Mariposa County.
Adair County, Oklahoma
AQI 45 · 59.2% good
Allen County, Indiana
AQI 45 · 58.2% good
Atascosa County, Texas
AQI 45 · 58.0% good
Baker County, Florida
AQI 45 · 69.1% good
Carson City County, Nevada
AQI 45 · 79.3% good
Clinton County, Iowa
AQI 45 · 59.9% good
What Mariposa 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 45 means for exposure. Health guidance
- See how Mariposa County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Mariposa County with its California neighbours before drawing a conclusion about the region. All of California
Based on 250 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 Mariposa County, California? ▼
Mariposa County has a median Air Quality Index (AQI) of 45, rated "Good." 81.6% of monitored days (204 out of 250) had good air quality in 2025.
What is the main pollutant in Mariposa County? ▼
The primary pollutant in Mariposa County is Ozone (O3), which was the main AQI driver on 249 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Mariposa County have? ▼
In 2025, Mariposa County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 90.
Is the air quality in Mariposa County getting better or worse? ▼
Air quality in Mariposa County is improving based on 5-year trends (2020-2025). Best year: 2024 with 255 good days. Worst year: 2021 with 193 good days.
What does AQI 45 mean for health? ▼
Mariposa County's median AQI of 45 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 Mariposa County compare to other counties in California? ▼
Mariposa County has 81.6% 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 Mariposa County? ▼
The 90th percentile AQI for Mariposa County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 90 (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.