Median AQI
37
Good
Pennsylvania · County air quality · 2025
Franklin County, Pennsylvania
Median AQI 37 (Good). 93.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 93.0%
- Good-air days
- 0
- Unhealthy days
- 83%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Franklin County's air is good on balance, cleaner than most US counties, a median AQI of 37 with 93.0% of 157 monitored days in the Good band, driven mainly by Ozone.
- 37
- median AQI · Good
- 93.0%
- days rated Good
- Ozone
- main pollutant
- 83%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 77.
Data updated July 2026
- Good · 146 d · 93.0%
- Moderate · 11 d · 7.0%
How did Franklin County's air break down in 2025?
Across 157 monitored days, 146 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 77 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 157 days monitored. Median AQI: 37 (Good).
Insights: Franklin County, Pennsylvania. EPA monitors recorded a median Air Quality Index of 37 across 157 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 146 (93%) fell in the Good band (AQI 0–50), 11 (7%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 47, while the worst single-day peak hit 77 (Moderate). Residents averaged about 27.9 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (157 days). Across the 2020–2025 trend window, good days shifted by -217 and the median AQI moved +5 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 77, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (73.8% good, AQI 42); Allegheny (51.6% good, AQI 49); Armstrong (68.1% good, AQI 42); Beaver (54.3% good, AQI 47); Berks (65.6% good, AQI 44); Blair (71.9% good, AQI 41).
Air Quality Summary
Good Days
93.0%
146 of 157 monitored days
18.0pp vs 75% target
Max AQI Recorded
77
Moderate
Health Grade
Excellent
90th-pct AQI 47
Franklin County, Good days share 93.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Franklin 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 157 monitored days across EPA AQI categories.
Good
146
93%
Moderate
11
7%
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 Franklin County.
- Ozone · 157 days · 100.0%
Health Impact Assessment
Excellent
Franklin County's air quality is rated Excellent based on 93.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 93.0% of monitored days in 2025, with a median AQI of 37. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 157 of 157 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Franklin County. Best year: 2020 (363 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 363 | 0 | 0 | 0 | 32 | 50 |
| 2021 | 274 | 14 | 0 | 0 | 35 | 77 |
| 2022 | 225 | 12 | 0 | 0 | 39 | 84 |
| 2023 | 267 | 32 | 2 | 0 | 39 | 133 |
| 2024 | 305 | 22 | 0 | 0 | 35 | 90 |
| 2025 | 146 | 11 | 0 | 0 | 37 | 77 |
How does Franklin County compare?
How Franklin County compares
Good-day share better than US avg
Franklin County 93.0%
Adams County, Pennsylvania 73.8%
US average 76.5%
Median AQI better than US avg
Franklin County 37
Adams County, Pennsylvania 42
US average 38
Unhealthy days / yr about average
Franklin County 0
Adams County, Pennsylvania 0
US average 0
Other Counties in Pennsylvania
Air quality comparison for nearby counties in Pennsylvania.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Franklin County.
Alachua County, Florida
AQI 37 · 90.1% good
Beltrami County, Minnesota
AQI 37 · 88.8% good
Benewah County, Idaho
AQI 37 · 74.6% good
Brevard County, Florida
AQI 37 · 89.7% good
Brown County, Indiana
AQI 37 · 94.5% good
Brown County, Wisconsin
AQI 37 · 79.0% good
What Franklin County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 37 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 Pennsylvania neighbours before drawing a conclusion about the region. All of Pennsylvania
Based on 157 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, Pennsylvania? ▼
Franklin County has a median Air Quality Index (AQI) of 37, rated "Good." 93.0% of monitored days (146 out of 157) had good air quality in 2025.
What is the main pollutant in Franklin County? ▼
The primary pollutant in Franklin County is Ozone (O3), which was the main AQI driver on 157 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Franklin County have? ▼
In 2025, Franklin County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 77.
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 363 good days. Worst year: 2025 with 146 good days.
What does AQI 37 mean for health? ▼
Franklin County's median AQI of 37 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 Franklin County compare to other counties in Pennsylvania? ▼
Franklin County has 93.0% good air days. Nearby counties in Pennsylvania: Adams (73.8% good), Allegheny (51.6% good), Armstrong (68.1% good), Beaver (54.3% good), Berks (65.6% good), Blair (71.9% good).
What is the 90th percentile AQI in Franklin County? ▼
The 90th percentile AQI for Franklin County is 47, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 77 (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.