What Is the Air Quality in Nez Perce, Idaho?
Nez Perce, Idaho has an Air Quality Grade of C (fair) with a 5-year median AQI of 33. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening over the past decade.
Nez Perce, Idaho Air Quality Snapshot
| Air Quality Grade | C58/100 |
| 5-Year Median AQI | 33 (Good) |
| Most Recent Median AQI (2023) | 36 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Worsening (+0.87 AQI/yr) |
| Unhealthy Days (last 5 yr) | 38 |
| National Rank (cleanest = #1) | #170 of 1,020 (17th cleanest percentile) |
| Idaho Rank | #9 of 20 |
What Does the C Grade Mean?
Nez Perce, Idaho earns a C — air quality is fair, but not great. With a 5-year median AQI of 33, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Nez Perce, Idaho's 5-year median AQI of 33 is 8 points below the national average of 41 — meaningfully cleaner than the typical U.S. metro tracked here. Within Idaho, Nez Perce, Idaho's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 33.
For context within Idaho: Custer, Idaho currently holds the state's cleanest grade (A, AQI 8), while Valley, Idaho sits at the bottom (D, AQI 37).
What's in Nez Perce, Idaho's Air?
The dominant pollutant in Nez Perce, Idaho is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 365 | 100% |
Is the Air Getting Better or Worse?
Air quality in Nez Perce, Idaho has been getting worse over the past decade, with median AQI climbing by roughly 0.9 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.
In 2015, Nez Perce, Idaho posted a median AQI of 25. By 2023 that figure was 36 — a rise of 11 AQI points dirtier across 9 years of EPA records.
Year-by-Year AQI in Nez Perce, Idaho
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2015 | 25 | 216 | 14 | PM2.5 |
| 2016 | 31 | 287 | 2 | PM2.5 |
| 2017 | 36 | 252 | 15 | PM2.5 |
| 2018 | 25 | 273 | 5 | PM2.5 |
| 2019 | 32 | 272 | 0 | PM2.5 |
| 2020 | 28 | 279 | 11 | PM2.5 |
| 2021 | 34 | 251 | 18 | PM2.5 |
| 2022 | 34 | 252 | 6 | PM2.5 |
| 2023 | 36 | 256 | 3 | PM2.5 |
Health Context for Nez Perce, Idaho
Across the past five years, this area has logged 38 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 8 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
Nez Perce, Idaho has an Air Quality Grade of C (fair) with a 5-year median AQI of 33. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.