Median AQI
29
Good
Idaho · County air quality · 2025
Nez Perce County, Idaho
Median AQI 29 (Good). 84.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 29
- Median AQI
- 84.0%
- Good-air days
- 0
- Unhealthy days
- 63%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Nez Perce County's air is good on balance, cleaner than the median US county, a median AQI of 29 with 84.0% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 29
- median AQI · Good
- 84.0%
- days rated Good
- PM2.5
- main pollutant
- 63%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 89.
Data updated July 2026
- Good · 152 d · 84.0%
- Moderate · 29 d · 16.0%
How did Nez Perce County's air break down in 2025?
Across 181 monitored days, 152 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 89 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 29 (Good).
Insights: Nez Perce County, Idaho. EPA monitors recorded a median Air Quality Index of 29 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 152 (84%) fell in the Good band (AQI 0–50), 29 (16%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 54, while the worst single-day peak hit 89 (Moderate). Residents averaged about 25.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (181 days). Across the 2020–2025 trend window, good days shifted by -127 and the median AQI moved +1 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 89, moderate but never Unhealthy. Nearby counties show comparable readings: Ada (80.6% good, AQI 39); Bannock (91.5% good, AQI 31); Benewah (74.6% good, AQI 37); Blaine (99.4% good, AQI 22); Boise (72.9% good, AQI 43); Bonner (71.3% good, AQI 41).
Air Quality Summary
Good Days
84.0%
152 of 181 monitored days
9.0pp vs 75% target
Max AQI Recorded
89
Moderate
Health Grade
Good
90th-pct AQI 54
Nez Perce County, Good days share 84.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Nez Perce 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 181 monitored days across EPA AQI categories.
Good
152
84%
Moderate
29
16%
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 Nez Perce County.
- PM2.5 · 181 days · 100.0%
Health Impact Assessment
Good
Nez Perce County's air quality is rated Good based on 84.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 84.0% of monitored days in 2025, with a median AQI of 29. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 181 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Nez Perce County. Best year: 2020 (279 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 279 | 76 | 4 | 0 | 28 | 475 |
| 2021 | 251 | 96 | 15 | 2 | 34 | 204 |
| 2022 | 252 | 107 | 2 | 4 | 34 | 195 |
| 2023 | 256 | 106 | 2 | 1 | 36 | 199 |
| 2024 | 276 | 82 | 7 | 1 | 29 | 182 |
| 2025 | 152 | 29 | 0 | 0 | 29 | 89 |
How does Nez Perce County compare?
How Nez Perce County compares
Good-day share better than US avg
Nez Perce County 84.0%
Ada County, Idaho 80.6%
US average 76.5%
Median AQI better than US avg
Nez Perce County 29
Ada County, Idaho 39
US average 38
Unhealthy days / yr about average
Nez Perce County 0
Ada County, Idaho 0
US average 0
Other Counties in Idaho
Air quality comparison for nearby counties in Idaho.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Nez Perce County.
Bayamon County, Puerto Rico
AQI 29 · 88.5% good
Fajardo County, Puerto Rico
AQI 29 · 85.7% good
Grant County, Oklahoma
AQI 29 · 90.0% good
Jackson County, Wisconsin
AQI 29 · 76.0% good
Roane County, Tennessee
AQI 29 · 84.1% good
Washington County, Nebraska
AQI 29 · 84.3% good
What Nez Perce 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 29 means for exposure. Health guidance
- See how Nez Perce County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Nez Perce County with its Idaho neighbours before drawing a conclusion about the region. All of Idaho
Based on 181 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 Nez Perce County, Idaho? ▼
Nez Perce County has a median Air Quality Index (AQI) of 29, rated "Good." 84.0% of monitored days (152 out of 181) had good air quality in 2025.
What is the main pollutant in Nez Perce County? ▼
The primary pollutant in Nez Perce County is Fine Particles (PM2.5), which was the main AQI driver on 181 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Nez Perce County have? ▼
In 2025, Nez Perce County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 89.
Is the air quality in Nez Perce County getting better or worse? ▼
Air quality in Nez Perce County is improving based on 5-year trends (2020-2025). Best year: 2020 with 279 good days. Worst year: 2025 with 152 good days.
What does AQI 29 mean for health? ▼
Nez Perce County's median AQI of 29 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 Nez Perce County compare to other counties in Idaho? ▼
Nez Perce County has 84.0% good air days. Nearby counties in Idaho: Ada (80.6% good), Bannock (91.5% good), Benewah (74.6% good), Blaine (99.4% good), Boise (72.9% good), Bonner (71.3% good).
What is the 90th percentile AQI in Nez Perce County? ▼
The 90th percentile AQI for Nez Perce County is 54, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 89 (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.