Median AQI
39
Good
Pennsylvania · County air quality · 2025
Westmoreland County, Pennsylvania
Median AQI 39 (Good). 73.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 73.9%
- Good-air days
- 0
- Unhealthy days
- 39%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Westmoreland County's air is good on balance, more polluted than the median US county, a median AQI of 39 with 73.9% of 207 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 73.9%
- days rated Good
- Ozone
- main pollutant
- 39%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 126.
Data updated July 2026
- Good · 153 d · 73.9%
- Moderate · 53 d · 25.6%
- USG · 1 d · 0.5%
How did Westmoreland County's air break down in 2025?
Across 207 monitored days, 153 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). 207 days monitored. Median AQI: 39 (Good).
Insights: Westmoreland County, Pennsylvania. EPA monitors recorded a median Air Quality Index of 39 across 207 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 153 (74%) fell in the Good band (AQI 0–50), 53 (26%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 126 (USG). Residents averaged about 22.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (121 days), PM2.5 (86 days). Across the 2020–2025 trend window, good days shifted by -128 and the median AQI moved +0 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: 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
73.9%
153 of 207 monitored days
-1.1pp vs 75% target
Max AQI Recorded
126
USG
Health Grade
Moderate
90th-pct AQI 61
Westmoreland County, Good days share 73.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Westmoreland 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 207 monitored days across EPA AQI categories.
Good
153
74%
Moderate
53
26%
USG
1
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 Westmoreland County.
- Ozone · 121 days · 58.5%
- PM2.5 · 86 days · 41.5%
Health Impact Assessment
Moderate
Westmoreland County's air quality is rated Moderate based on 73.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 73.9% of monitored days in 2025, with a median AQI of 39. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 121 of 207 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Westmoreland County. Best year: 2020 (281 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 281 | 81 | 0 | 0 | 39 | 83 |
| 2021 | 196 | 157 | 1 | 0 | 47 | 124 |
| 2022 | 198 | 106 | 0 | 0 | 41 | 76 |
| 2023 | 227 | 70 | 1 | 0 | 42 | 133 |
| 2024 | 278 | 85 | 0 | 0 | 39 | 88 |
| 2025 | 153 | 53 | 1 | 0 | 39 | 126 |
How does Westmoreland County compare?
How Westmoreland County compares
Good-day share worse than US avg
Westmoreland County 73.9%
Adams County, Pennsylvania 73.8%
US average 76.5%
Median AQI worse than US avg
Westmoreland County 39
Adams County, Pennsylvania 42
US average 38
Unhealthy days / yr about average
Westmoreland 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 Westmoreland County.
Ada County, Idaho
AQI 39 · 80.6% good
Aiken County, South Carolina
AQI 39 · 89.1% good
Albany County, New York
AQI 39 · 67.4% good
Alexander County, North Carolina
AQI 39 · 92.4% good
Ashland County, Wisconsin
AQI 39 · 85.6% good
Bennington County, Vermont
AQI 39 · 82.9% good
What Westmoreland 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 39 means for exposure. Health guidance
- See how Westmoreland County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Westmoreland County with its Pennsylvania neighbours before drawing a conclusion about the region. All of Pennsylvania
Based on 207 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 Westmoreland County, Pennsylvania? ▼
Westmoreland County has a median Air Quality Index (AQI) of 39, rated "Good." 73.9% of monitored days (153 out of 207) had good air quality in 2025.
What is the main pollutant in Westmoreland County? ▼
The primary pollutant in Westmoreland County is Ozone (O3), which was the main AQI driver on 121 days (58% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Westmoreland County have? ▼
In 2025, Westmoreland County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 126.
Is the air quality in Westmoreland County getting better or worse? ▼
Air quality in Westmoreland County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 281 good days. Worst year: 2025 with 153 good days.
What does AQI 39 mean for health? ▼
Westmoreland County's median AQI of 39 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 Westmoreland County compare to other counties in Pennsylvania? ▼
Westmoreland County has 73.9% 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 Westmoreland County? ▼
The 90th percentile AQI for Westmoreland County is 61, 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.