Median AQI
54
Moderate
Ohio · County air quality · 2025
Franklin County, Ohio
Median AQI 54 (Moderate). 39.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 54
- Median AQI
- 39.8%
- Good-air days
- 1
- Unhealthy days
- 3%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Franklin County's air is moderate on balance, among the most polluted counties nationally, a median AQI of 54 with 39.8% of 274 monitored days in the Good band, driven mainly by PM2.5.
- 54
- median AQI · Moderate
- 39.8%
- days rated Good
- PM2.5
- main pollutant
- 3%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 156.
Data updated July 2026
- Good · 109 d · 39.8%
- Moderate · 160 d · 58.4%
- USG · 4 d · 1.5%
- Unhealthy · 1 d · 0.4%
How did Franklin County's air break down in 2025?
Across 274 monitored days, 109 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 156 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 274 days monitored. Median AQI: 54 (Moderate).
Insights: Franklin County, Ohio. EPA monitors recorded a median Air Quality Index of 54 across 274 measured days in 2025, earning a Moderate classification and a Poor health grade. Of those days, 109 (40%) fell in the Good band (AQI 0–50), 160 (58%) registered Moderate readings, and 4 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 76, while the worst single-day peak hit 156 (Unhealthy). Residents averaged about 11.9 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (183 days), Ozone (84 days), PM10 (6 days), CO (1 days). Across the 2020–2025 trend window, good days shifted by -123 and the median AQI moved +9 points, placing the multi-year trajectory at worsening. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. 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); Clark (59.4% good, AQI 46).
Air Quality Summary
Good Days
39.8%
109 of 274 monitored days
-35.2pp vs 75% target
Max AQI Recorded
156
Unhealthy
Health Grade
Poor
90th-pct AQI 76
Franklin County, Good days share 39.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Franklin County, Unhealthy-or-worse share 0.4%
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 274 monitored days across EPA AQI categories.
Good
109
40%
Moderate
160
58%
USG
4
1%
Unhealthy
1
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Franklin County.
- PM2.5 · 183 days · 66.8%
- Ozone · 84 days · 30.7%
- PM10 · 6 days · 2.2%
- CO · 1 days · 0.4%
Health Impact Assessment
Poor
Franklin County's air quality is rated Poor based on 39.8% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 4 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 156. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 183 of 274 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Franklin County. Best year: 2020 (232 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 232 | 132 | 2 | 0 | 45 | 102 |
| 2021 | 170 | 195 | 0 | 0 | 52 | 100 |
| 2022 | 206 | 157 | 2 | 0 | 48 | 143 |
| 2023 | 136 | 218 | 7 | 3 | 54 | 210 |
| 2024 | 151 | 211 | 4 | 0 | 53 | 118 |
| 2025 | 109 | 160 | 4 | 1 | 54 | 156 |
How does Franklin County compare?
How Franklin County compares
Good-day share worse than US avg
Franklin County 39.8%
Allen County, Ohio 65.9%
US average 76.5%
Median AQI worse than US avg
Franklin County 54
Allen County, Ohio 43
US average 38
Unhealthy days / yr worse than US avg
Franklin County 1
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 Franklin County.
Denver County, Colorado
AQI 54 · 44.2% good
Fresno County, California
AQI 54 · 40.1% good
Hamilton County, Ohio
AQI 54 · 32.1% good
Hidalgo County, Texas
AQI 54 · 36.2% good
Inyo County, California
AQI 54 · 40.7% good
Larimer County, Colorado
AQI 54 · 40.1% good
What Franklin County's air means for you
On most days the air here is fine, but PM2.5 drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 54 means for exposure. Health guidance
- See how Franklin County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Franklin County with its Ohio neighbours before drawing a conclusion about the region. All of Ohio
Based on 274 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 Franklin County, Ohio? ▼
Franklin County has a median Air Quality Index (AQI) of 54, rated "Moderate." 39.8% of monitored days (109 out of 274) had good air quality in 2025.
What is the main pollutant in Franklin County? ▼
The primary pollutant in Franklin County is Fine Particles (PM2.5), which was the main AQI driver on 183 days (67% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Franklin County have? ▼
In 2025, Franklin County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 156.
Is the air quality in Franklin County getting better or worse? ▼
Air quality in Franklin County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 232 good days. Worst year: 2025 with 109 good days.
What does AQI 54 mean for health? ▼
Franklin County's median AQI of 54 falls in the "Moderate" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Franklin County compare to other counties in Ohio? ▼
Franklin County has 39.8% 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), Clark (59.4% good).
What is the 90th percentile AQI in Franklin County? ▼
The 90th percentile AQI for Franklin County is 76, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 156 (Unhealthy).
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.