Median AQI
19
Good
Washington · County air quality · 2025
Grays Harbor County, Washington
Median AQI 19 (Good). 97.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 19
- Median AQI
- 97.9%
- Good-air days
- 0
- Unhealthy days
- 95%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Grays Harbor County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 19 with 97.9% of 243 monitored days in the Good band, driven mainly by PM2.5.
- 19
- median AQI · Good
- 97.9%
- 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 76.
Data updated July 2026
- Good · 238 d · 97.9%
- Moderate · 5 d · 2.1%
How did Grays Harbor County's air break down in 2025?
Across 243 monitored days, 238 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 76 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 19 (Good).
Insights: Grays Harbor County, Washington. EPA monitors recorded a median Air Quality Index of 19 across 243 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 238 (98%) fell in the Good band (AQI 0–50), 5 (2%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 36, while the worst single-day peak hit 76 (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 (243 days). Across the 2020–2025 trend window, good days shifted by -92 and the median AQI moved -8 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 76, 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
97.9%
238 of 243 monitored days
22.9pp vs 75% target
Max AQI Recorded
76
Moderate
Health Grade
Excellent
90th-pct AQI 36
Grays Harbor County, Good days share 97.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Grays Harbor 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 243 monitored days across EPA AQI categories.
Good
238
98%
Moderate
5
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 Grays Harbor County.
- PM2.5 · 243 days · 100.0%
Health Impact Assessment
Excellent
Grays Harbor County's air quality is rated Excellent based on 97.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 97.9% of monitored days in 2025, with a median AQI of 19. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 243 of 243 monitored days.
5-Year Air Quality Trend
Air quality is improving in Grays Harbor County. Best year: 2024 (353 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 330 | 28 | 1 | 2 | 27 | 242 |
| 2021 | 347 | 18 | 0 | 0 | 26 | 82 |
| 2022 | 340 | 24 | 1 | 0 | 22 | 112 |
| 2023 | 339 | 26 | 0 | 0 | 23 | 80 |
| 2024 | 353 | 13 | 0 | 0 | 20 | 64 |
| 2025 | 238 | 5 | 0 | 0 | 19 | 76 |
How does Grays Harbor County compare?
How Grays Harbor County compares
Good-day share better than US avg
Grays Harbor County 97.9%
Adams County, Washington 94.7%
US average 76.5%
Median AQI better than US avg
Grays Harbor County 19
Adams County, Washington 19
US average 38
Unhealthy days / yr about average
Grays Harbor 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 Grays Harbor County.
Adams County, Washington
AQI 19 · 94.7% good
Bonneville County, Idaho
AQI 19 · 94.9% good
Elko County, Nevada
AQI 19 · 90.8% good
Jefferson County, Washington
AQI 19 · 96.5% good
Luna County, New Mexico
AQI 19 · 79.5% good
Mohave County, Arizona
AQI 19 · 93.4% good
What Grays Harbor 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 19 means for exposure. Health guidance
- See how Grays Harbor County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Grays Harbor County with its Washington neighbours before drawing a conclusion about the region. All of Washington
Based on 243 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 Grays Harbor County, Washington? ▼
Grays Harbor County has a median Air Quality Index (AQI) of 19, rated "Good." 97.9% of monitored days (238 out of 243) had good air quality in 2025.
What is the main pollutant in Grays Harbor County? ▼
The primary pollutant in Grays Harbor County is Fine Particles (PM2.5), which was the main AQI driver on 243 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Grays Harbor County have? ▼
In 2025, Grays Harbor County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 76.
Is the air quality in Grays Harbor County getting better or worse? ▼
Air quality in Grays Harbor County is improving based on 5-year trends (2020-2025). Best year: 2024 with 353 good days. Worst year: 2025 with 238 good days.
What does AQI 19 mean for health? ▼
Grays Harbor County's median AQI of 19 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 Grays Harbor County compare to other counties in Washington? ▼
Grays Harbor County has 97.9% 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 Grays Harbor County? ▼
The 90th percentile AQI for Grays Harbor County is 36, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 76 (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.