Median AQI
31
Good
Washington · County air quality · 2025
Clark County, Washington
Median AQI 31 (Good). 89.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 31
- Median AQI
- 89.3%
- Good-air days
- 0
- Unhealthy days
- 74%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Clark County's air is good on balance, cleaner than the median US county, a median AQI of 31 with 89.3% of 243 monitored days in the Good band, driven mainly by PM2.5.
- 31
- median AQI · Good
- 89.3%
- days rated Good
- PM2.5
- main pollutant
- 74%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 80.
Data updated July 2026
- Good · 217 d · 89.3%
- Moderate · 26 d · 10.7%
How did Clark County's air break down in 2025?
Across 243 monitored days, 217 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 80 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 31 (Good).
Insights: Clark County, Washington. EPA monitors recorded a median Air Quality Index of 31 across 243 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 217 (89%) fell in the Good band (AQI 0–50), 26 (11%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 51, while the worst single-day peak hit 80 (Moderate). Residents averaged about 26.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (135 days), Ozone (108 days). Across the 2020–2025 trend window, good days shifted by -55 and the median AQI moved -1 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 80, 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); Columbia (93.0% good, AQI 37).
Air Quality Summary
Good Days
89.3%
217 of 243 monitored days
14.3pp vs 75% target
Max AQI Recorded
80
Moderate
Health Grade
Good
90th-pct AQI 51
Clark County, Good days share 89.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Clark 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
217
89%
Moderate
26
11%
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 Clark County.
- PM2.5 · 135 days · 55.6%
- Ozone · 108 days · 44.4%
Health Impact Assessment
Good
Clark County's air quality is rated Good based on 89.3% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 89.3% of monitored days in 2025, with a median AQI of 31. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 135 of 243 monitored days.
5-Year Air Quality Trend
Air quality is improving in Clark County. Best year: 2024 (321 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 272 | 85 | 1 | 0 | 32 | 874 |
| 2021 | 308 | 57 | 0 | 0 | 34 | 98 |
| 2022 | 267 | 93 | 2 | 3 | 36 | 175 |
| 2023 | 281 | 82 | 0 | 2 | 35 | 153 |
| 2024 | 321 | 44 | 1 | 0 | 31 | 105 |
| 2025 | 217 | 26 | 0 | 0 | 31 | 80 |
How does Clark County compare?
How Clark County compares
Good-day share better than US avg
Clark County 89.3%
Adams County, Washington 94.7%
US average 76.5%
Median AQI better than US avg
Clark County 31
Adams County, Washington 19
US average 38
Unhealthy days / yr about average
Clark 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 Clark County.
Bannock County, Idaho
AQI 31 · 91.5% good
Erie County, Pennsylvania
AQI 31 · 81.4% good
Honolulu County, Hawaii
AQI 31 · 95.0% good
Josephine County, Oregon
AQI 31 · 76.2% good
Monroe County, Wisconsin
AQI 31 · 75.2% good
Montgomery County, Tennessee
AQI 31 · 84.7% good
What Clark 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 31 means for exposure. Health guidance
- See how Clark County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Clark 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 Clark County, Washington? ▼
Clark County has a median Air Quality Index (AQI) of 31, rated "Good." 89.3% of monitored days (217 out of 243) had good air quality in 2025.
What is the main pollutant in Clark County? ▼
The primary pollutant in Clark County is Fine Particles (PM2.5), which was the main AQI driver on 135 days (56% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Clark County have? ▼
In 2025, Clark County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 80.
Is the air quality in Clark County getting better or worse? ▼
Air quality in Clark County is improving based on 5-year trends (2020-2025). Best year: 2024 with 321 good days. Worst year: 2025 with 217 good days.
What does AQI 31 mean for health? ▼
Clark County's median AQI of 31 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 Clark County compare to other counties in Washington? ▼
Clark County has 89.3% 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), Columbia (93.0% good).
What is the 90th percentile AQI in Clark County? ▼
The 90th percentile AQI for Clark County is 51, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 80 (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.