California · County air quality · 2025
Nevada County, California
Median AQI 42 (Good). 79.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 79.8%
- Good-air days
- 0
- Unhealthy days
- 56%
- Cleaner than US counties
Nevada County's 2025 annual median AQI is 42 (Good), with 79.8% Good days
According to the U.S. EPA Air Quality System, Nevada County, California posted a 2025 median AQI of 42 (Good) across 362 monitored days, with 79.8% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Nevada County's 79.8% Good-day share places it cleaner than 56% of US counties in 2025.
- Closest median-AQI peer
- Ada County (74.0% Good, median AQI 42) is the closest nationwide median-AQI peer to Nevada County.
- 2020–2025 trend
- Nevada County's floor-qualifying Good-day share is improving from 2020 to 2025 (61.9% → 79.8%).
- Median AQI
- Median AQI: 42
According to the 2025 EPA AQS county release on PlainAirData, Nevada County, California ranks #581 of 951 by median AQI (42) and #418 by good-day share (79.8%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.
Annual release change
What changed in the 2025 EPA annual release
- Nevada County's Good-day share fell from 85.8% to 79.8% between the 2024 and 2025 EPA annual releases, a change of -5.9 percentage points.
- Nevada County's peak single-day AQI fell from 132 to 108 between the 2024 and 2025 EPA annual releases, a change of -24 points.
- Nevada County's median AQI rose from 36 to 42 between the 2024 and 2025 EPA annual releases, a change of +6 points.
Data updated August 2026
- Good · 289 d · 79.8%
- Moderate · 72 d · 19.9%
- USG · 1 d · 0.3%
How did Nevada County's air break down in 2025?
Across 362 monitored days, 289 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
EPA AQS →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where Nevada County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Nevada County's Good-day share is 79.8% - cleaner than 56% of that comparison set.
Nevada County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
79.8% Cleaner than 56% higher than 56% of 951 US counties
Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Nevada County.
- Ozone · 250 days · 69.1%
- PM2.5 · 112 days · 30.9%
2024 daily-monitor rhythm in Nevada County
Month-by-month median AQI from EPA day-level county monitors (365 reported days in 2024). Aug posted the highest typical readings (median AQI 63, peak 105); Mar was cleanest at median 14. Summer months (Jun–Aug) averaged median AQI 45 vs 29 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–20241,824 daily readings show a recurring local pattern: Aug has the highest matched-month median AQI (81), while Mar is lowest (37). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
Nevada County's air quality is rated Good based on 79.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 79.8% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 250 of 362 monitored days.
5-Year Air Quality Trend
Air quality is improving in Nevada County. Highest Good-day share: 2024 (85.8%, 313 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 223 | 111 | 15 | 11 | 46 | 277 |
| 2021 | 183 | 129 | 34 | 13 | 50 | 326 |
| 2022 | 185 | 161 | 11 | 3 | 50 | 293 |
| 2023 | 282 | 81 | 0 | 0 | 42 | 97 |
| 2024 | 313 | 50 | 2 | 0 | 36 | 132 |
| 2025 | 289 | 72 | 1 | 0 | 42 | 108 |
How does Nevada County compare?
How Nevada County compares
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Nevada County, California · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
Every figure on PlainAirData 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.