Median AQI
26
Good
Washington · County air quality · 2025
Thurston County, Washington
Median AQI 26 (Good). 98.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 26
- Median AQI
- 98.1%
- Good-air days
- 0
- Unhealthy days
- 95%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Thurston County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 26 with 98.1% of 161 monitored days in the Good band, driven mainly by PM2.5.
- 26
- median AQI · Good
- 98.1%
- days rated Good
- PM2.5
- main pollutant
- 95%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 52.
Data updated July 2026
- Good · 158 d · 98.1%
- Moderate · 3 d · 1.9%
How did Thurston County's air break down in 2025?
Across 161 monitored days, 158 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 52 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 161 days monitored. Median AQI: 26 (Good).
Insights: Thurston County, Washington. EPA monitors recorded a median Air Quality Index of 26 across 161 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 158 (98%) fell in the Good band (AQI 0–50), 3 (2%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 44, while the worst single-day peak hit 52 (Moderate). Residents averaged about 29.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (104 days), Ozone (57 days). Across the 2020–2025 trend window, good days shifted by -158 and the median AQI moved -2 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 52, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (94.7% good, AQI 19); Asotin (73.8% good, AQI 35); Benton (88.9% good, AQI 35); Chelan (87.2% good, AQI 27); Clallam (88.5% good, AQI 26); Clark (89.3% good, AQI 31).
Air Quality Summary
Good Days
98.1%
158 of 161 monitored days
23.1pp vs 75% target
Max AQI Recorded
52
Moderate
Health Grade
Excellent
90th-pct AQI 44
Thurston County, Good days share 98.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Thurston 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 161 monitored days across EPA AQI categories.
Good
158
98%
Moderate
3
2%
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 Thurston County.
- PM2.5 · 104 days · 64.6%
- Ozone · 57 days · 35.4%
Health Impact Assessment
Excellent
Thurston County's air quality is rated Excellent based on 98.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 98.1% of monitored days in 2025, with a median AQI of 26. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 104 of 161 monitored days.
5-Year Air Quality Trend
Air quality is improving in Thurston County. Best year: 2024 (338 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 316 | 43 | 0 | 3 | 28 | 242 |
| 2021 | 309 | 20 | 0 | 0 | 19 | 63 |
| 2022 | 309 | 36 | 1 | 2 | 28 | 157 |
| 2023 | 327 | 31 | 0 | 0 | 28 | 82 |
| 2024 | 338 | 24 | 0 | 0 | 26 | 85 |
| 2025 | 158 | 3 | 0 | 0 | 26 | 52 |
How does Thurston County compare?
How Thurston County compares
Good-day share better than US avg
Thurston County 98.1%
Adams County, Washington 94.7%
US average 76.5%
Median AQI better than US avg
Thurston County 26
Adams County, Washington 19
US average 38
Unhealthy days / yr about average
Thurston County 0
Adams County, Washington 0
US average 0
Other Counties in Washington
Air quality comparison for nearby counties in Washington.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Thurston County.
Clallam County, Washington
AQI 26 · 88.5% good
Ford County, Kansas
AQI 26 · 89.4% good
Grant County, Washington
AQI 26 · 89.7% good
Harney County, Oregon
AQI 26 · 70.7% good
Taney County, Missouri
AQI 26 · 100.0% good
Wyoming County, Pennsylvania
AQI 26 · 83.1% good
What Thurston 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 26 means for exposure. Health guidance
- See how Thurston County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Thurston County with its Washington neighbours before drawing a conclusion about the region. All of Washington
Based on 161 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 Thurston County, Washington? ▼
Thurston County has a median Air Quality Index (AQI) of 26, rated "Good." 98.1% of monitored days (158 out of 161) had good air quality in 2025.
What is the main pollutant in Thurston County? ▼
The primary pollutant in Thurston County is Fine Particles (PM2.5), which was the main AQI driver on 104 days (65% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Thurston County have? ▼
In 2025, Thurston County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 52.
Is the air quality in Thurston County getting better or worse? ▼
Air quality in Thurston County is improving based on 5-year trends (2020-2025). Best year: 2024 with 338 good days. Worst year: 2025 with 158 good days.
What does AQI 26 mean for health? ▼
Thurston County's median AQI of 26 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 Thurston County compare to other counties in Washington? ▼
Thurston County has 98.1% good air days. Nearby counties in Washington: Adams (94.7% good), Asotin (73.8% good), Benton (88.9% good), Chelan (87.2% good), Clallam (88.5% good), Clark (89.3% good).
What is the 90th percentile AQI in Thurston County? ▼
The 90th percentile AQI for Thurston County is 44, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 52 (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.