Washington · County air quality · 2025
Walla Walla County, Washington
Median AQI 28 (Good). 80.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 28
- Median AQI
- 80.8%
- Good-air days
- 0
- Unhealthy days
- 58%
- Cleaner than US counties
Walla Walla County's 2025 annual median AQI is 28 (Good), with 80.8% Good days
According to the U.S. EPA Air Quality System, Walla Walla County, Washington posted a 2025 median AQI of 28 (Good) across 365 monitored days, with 80.8% 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
- Walla Walla County's 80.8% Good-day share places it cleaner than 58% of US counties in 2025.
- Closest median-AQI peer
- Cass County (82.7% Good, median AQI 28) is the closest nationwide median-AQI peer to Walla Walla County.
- 2020–2025 trend
- Walla Walla County's floor-qualifying Good-day share is stable from 2020 to 2025 (83.0% → 80.8%).
- Median AQI
- Median AQI: 28
According to the 2025 EPA AQS county release on PlainAirData, Walla Walla County, Washington ranks #81 of 951 by median AQI (28) and #394 by good-day share (80.8%). 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
- Walla Walla County's Good-day share fell from 85.8% to 80.8% between the 2024 and 2025 EPA annual releases, a change of -5.0 percentage points.
- Walla Walla County's median AQI rose from 24 to 28 between the 2024 and 2025 EPA annual releases, a change of +4 points.
Data updated August 2026
- Good · 295 d · 80.8%
- Moderate · 70 d · 19.2%
How did Walla Walla County's air break down in 2025?
Across 365 monitored days, 295 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 85 (Moderate).
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 Walla Walla County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Walla Walla County's Good-day share is 80.8% - cleaner than 58% of that comparison set.
Walla Walla County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
80.8% Cleaner than 58% higher than 58% 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 Walla Walla County.
- PM2.5 · 251 days · 68.8%
- PM10 · 114 days · 31.2%
2024 daily-monitor rhythm in Walla Walla County
Month-by-month median AQI from EPA day-level county monitors (366 reported days in 2024). Aug posted the highest typical readings (median AQI 44, peak 74); Mar was cleanest at median 15. Summer months (Jun–Aug) averaged median AQI 35 vs 25 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–20241,827 daily readings show a recurring local pattern: Aug has the highest matched-month median AQI (41), while May is lowest (17). 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
Walla Walla County's air quality is rated Good based on 80.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 80.8% of monitored days in 2025, with a median AQI of 28. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 251 of 365 monitored days.
5-Year Air Quality Trend
Air quality is stable in Walla Walla County. Highest Good-day share: 2024 (85.8%, 314 of 366 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 297 | 60 | 0 | 1 | 26 | 855 |
| 2021 | 309 | 51 | 3 | 2 | 24 | 172 |
| 2022 | 292 | 70 | 2 | 1 | 25 | 152 |
| 2023 | 300 | 61 | 1 | 1 | 28 | 305 |
| 2024 | 314 | 52 | 0 | 0 | 24 | 87 |
| 2025 | 295 | 70 | 0 | 0 | 28 | 85 |
How does Walla Walla County compare?
How Walla Walla 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 Walla Walla 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.