Washington · County air quality · 2025
Asotin County, Washington
Median AQI 42 (Good). 61.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 61.9%
- Good-air days
- 1
- Unhealthy days
- 17%
- Cleaner than US counties
Asotin County's 2025 annual median AQI is 42 (Good), with 61.9% Good days
According to the U.S. EPA Air Quality System, Asotin County, Washington posted a 2025 median AQI of 42 (Good) across 362 monitored days, with 61.9% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Asotin County's 61.9% Good-day share places it cleaner than 17% 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 Asotin County.
- 2020–2025 trend
- Asotin County's floor-qualifying Good-day share is worsening from 2020 to 2025 (66.6% → 61.9%).
- Median AQI
- Median AQI: 42
According to the 2025 EPA AQS county release on PlainAirData, Asotin County, Washington ranks #581 of 951 by median AQI (42) and #786 by good-day share (61.9%). 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
- Asotin County's peak single-day AQI fell from 196 to 151 between the 2024 and 2025 EPA annual releases, a change of -45 points.
- Asotin County's Unhealthy-category days fell from 4 to 1 between the 2024 and 2025 EPA annual releases, a change of -3 days.
Data updated August 2026
- Good · 224 d · 61.9%
- Moderate · 135 d · 37.3%
- USG · 2 d · 0.6%
- Unhealthy · 1 d · 0.3%
How did Asotin County's air break down in 2025?
Across 362 monitored days, 224 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 151 (Unhealthy).
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 Asotin County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Asotin County's Good-day share is 61.9% - cleaner than 17% of that comparison set.
Asotin County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
61.9% 17th percentile higher than 17% 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 Asotin County.
- PM2.5 · 362 days · 100.0%
2024 daily-monitor rhythm in Asotin County
Month-by-month median AQI from EPA day-level county monitors (361 reported days in 2024). Jul posted the highest typical readings (median AQI 62, peak 196); Apr was cleanest at median 24. Summer months (Jun–Aug) averaged median AQI 50 vs 47 in Dec–Feb. 4 days crossed Unhealthy (AQI >150) at least once that year.
Five-year seasonal record
EPA day-level county files · 2020–20241,763 daily readings show a recurring local pattern: Aug has the highest matched-month median AQI (56), while May is lowest (30). 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
Asotin County's air quality is rated Moderate based on 61.9% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 2 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 151. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 362 of 362 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Asotin County. Highest Good-day share: 2020 (66.6%, 229 of 350 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 229 | 112 | 2 | 1 | 38 | 328 |
| 2021 | 176 | 140 | 14 | 4 | 48 | 233 |
| 2022 | 195 | 156 | 3 | 4 | 46 | 200 |
| 2023 | 184 | 169 | 4 | 1 | 49 | 204 |
| 2024 | 224 | 131 | 2 | 4 | 42 | 196 |
| 2025 | 224 | 135 | 2 | 1 | 42 | 151 |
How does Asotin County compare?
How Asotin 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 Asotin County, Washington · 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.