Median AQI
37
Good
Pennsylvania · County air quality · 2025
Somerset County, Pennsylvania
Median AQI 37 (Good). 94.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 94.2%
- Good-air days
- 0
- Unhealthy days
- 86%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Somerset County's air is good on balance, cleaner than most US counties, a median AQI of 37 with 94.2% of 243 monitored days in the Good band, driven mainly by Ozone.
- 37
- median AQI · Good
- 94.2%
- days rated Good
- Ozone
- main pollutant
- 86%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 93.
Data updated July 2026
- Good · 229 d · 94.2%
- Moderate · 14 d · 5.8%
How did Somerset County's air break down in 2025?
Across 243 monitored days, 229 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 93 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 37 (Good).
Insights: Somerset County, Pennsylvania. EPA monitors recorded a median Air Quality Index of 37 across 243 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 229 (94%) fell in the Good band (AQI 0–50), 14 (6%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 46, while the worst single-day peak hit 93 (Moderate). Residents averaged about 28.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (243 days). Across the 2020–2025 trend window, good days shifted by -128 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 93, 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
94.2%
229 of 243 monitored days
19.2pp vs 75% target
Max AQI Recorded
93
Moderate
Health Grade
Excellent
90th-pct AQI 46
Somerset County, Good days share 94.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Somerset 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
229
94%
Moderate
14
6%
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 Somerset County.
- Ozone · 243 days · 100.0%
Health Impact Assessment
Excellent
Somerset County's air quality is rated Excellent based on 94.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 94.2% 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 243 of 243 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Somerset County. Best year: 2020 (357 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 357 | 8 | 0 | 0 | 34 | 71 |
| 2021 | 339 | 24 | 0 | 0 | 34 | 90 |
| 2022 | 351 | 9 | 0 | 0 | 34 | 90 |
| 2023 | 333 | 32 | 0 | 0 | 35 | 93 |
| 2024 | 323 | 35 | 0 | 0 | 37 | 90 |
| 2025 | 229 | 14 | 0 | 0 | 37 | 93 |
How does Somerset County compare?
How Somerset County compares
Good-day share better than US avg
Somerset County 94.2%
Adams County, Pennsylvania 73.8%
US average 76.5%
Median AQI better than US avg
Somerset County 37
Adams County, Pennsylvania 42
US average 38
Unhealthy days / yr about average
Somerset 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 Somerset 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 Somerset 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 Somerset County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Somerset County with its Pennsylvania neighbours before drawing a conclusion about the region. All of Pennsylvania
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 Somerset County, Pennsylvania? ▼
Somerset County has a median Air Quality Index (AQI) of 37, rated "Good." 94.2% of monitored days (229 out of 243) had good air quality in 2025.
What is the main pollutant in Somerset County? ▼
The primary pollutant in Somerset County is Ozone (O3), which was the main AQI driver on 243 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Somerset County have? ▼
In 2025, Somerset County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 93.
Is the air quality in Somerset County getting better or worse? ▼
Air quality in Somerset County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 357 good days. Worst year: 2025 with 229 good days.
What does AQI 37 mean for health? ▼
Somerset 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 Somerset County compare to other counties in Pennsylvania? ▼
Somerset County has 94.2% 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 Somerset County? ▼
The 90th percentile AQI for Somerset County is 46, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 93 (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.