Median AQI
46
Good
Ohio · County air quality · 2025
Clark County, Ohio
Median AQI 46 (Good). 59.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 46
- Median AQI
- 59.4%
- Good-air days
- 0
- Unhealthy days
- 14%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Clark County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 46 with 59.4% of 271 monitored days in the Good band, driven mainly by PM2.5.
- 46
- median AQI · Good
- 59.4%
- days rated Good
- PM2.5
- main pollutant
- 14%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 126.
Data updated July 2026
- Good · 161 d · 59.4%
- Moderate · 108 d · 39.9%
- USG · 2 d · 0.7%
How did Clark County's air break down in 2025?
Across 271 monitored days, 161 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 126 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 271 days monitored. Median AQI: 46 (Good).
Insights: Clark County, Ohio. EPA monitors recorded a median Air Quality Index of 46 across 271 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 161 (59%) fell in the Good band (AQI 0–50), 108 (40%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 67, while the worst single-day peak hit 126 (USG). Residents averaged about 17.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (152 days), Ozone (119 days). Across the 2020–2025 trend window, good days shifted by -57 and the median AQI moved +2 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 126, usg but never Unhealthy. Nearby counties show comparable readings: Allen (65.9% good, AQI 43); Ashtabula (81.2% good, AQI 43); Athens (80.3% good, AQI 33); Belmont (63.0% good, AQI 42); Butler (33.3% good, AQI 55); Clermont (72.1% good, AQI 43).
Air Quality Summary
Good Days
59.4%
161 of 271 monitored days
-15.6pp vs 75% target
Max AQI Recorded
126
USG
Health Grade
Moderate
90th-pct AQI 67
Clark County, Good days share 59.4%
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 271 monitored days across EPA AQI categories.
Good
161
59%
Moderate
108
40%
USG
2
1%
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 · 152 days · 56.1%
- Ozone · 119 days · 43.9%
Health Impact Assessment
Moderate
Clark County's air quality is rated Moderate based on 59.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 59.4% of monitored days in 2025, with a median AQI of 46. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 152 of 271 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Clark County. Best year: 2024 (239 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 218 | 124 | 1 | 0 | 44 | 108 |
| 2021 | 169 | 196 | 0 | 0 | 52 | 100 |
| 2022 | 212 | 125 | 1 | 0 | 46 | 129 |
| 2023 | 187 | 170 | 5 | 3 | 50 | 196 |
| 2024 | 239 | 121 | 3 | 0 | 45 | 133 |
| 2025 | 161 | 108 | 2 | 0 | 46 | 126 |
How does Clark County compare?
How Clark County compares
Good-day share worse than US avg
Clark County 59.4%
Allen County, Ohio 65.9%
US average 76.5%
Median AQI worse than US avg
Clark County 46
Allen County, Ohio 43
US average 38
Unhealthy days / yr about average
Clark County 0
Allen County, Ohio 0
US average 0
Other Counties in Ohio
Air quality comparison for nearby counties in Ohio.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Clark County.
Bay County, Florida
AQI 46 · 60.6% good
Blount County, Tennessee
AQI 46 · 69.6% good
Cache County, Utah
AQI 46 · 61.2% good
Chesterfield County, South Carolina
AQI 46 · 61.2% good
Clark County, Indiana
AQI 46 · 59.7% good
Cochise County, Arizona
AQI 46 · 65.6% 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 46 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 Ohio neighbours before drawing a conclusion about the region. All of Ohio
Based on 271 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, Ohio? ▼
Clark County has a median Air Quality Index (AQI) of 46, rated "Good." 59.4% of monitored days (161 out of 271) 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 152 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 126.
Is the air quality in Clark County getting better or worse? ▼
Air quality in Clark County is worsening based on 5-year trends (2020-2025). Best year: 2024 with 239 good days. Worst year: 2025 with 161 good days.
What does AQI 46 mean for health? ▼
Clark County's median AQI of 46 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 Ohio? ▼
Clark County has 59.4% good air days. Nearby counties in Ohio: Allen (65.9% good), Ashtabula (81.2% good), Athens (80.3% good), Belmont (63.0% good), Butler (33.3% good), Clermont (72.1% good).
What is the 90th percentile AQI in Clark County? ▼
The 90th percentile AQI for Clark County is 67, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 126 (USG).
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.