Median AQI
41
Good
West Virginia · County air quality · 2025
Marshall County, West Virginia
Median AQI 41 (Good). 63.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 41
- Median AQI
- 63.6%
- Good-air days
- 0
- Unhealthy days
- 20%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Marshall County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 41 with 63.6% of 154 monitored days in the Good band, driven mainly by PM2.5.
- 41
- median AQI · Good
- 63.6%
- days rated Good
- PM2.5
- main pollutant
- 20%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 81.
Data updated July 2026
- Good · 98 d · 63.6%
- Moderate · 56 d · 36.4%
How did Marshall County's air break down in 2025?
Across 154 monitored days, 98 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 81 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 154 days monitored. Median AQI: 41 (Good).
Insights: Marshall County, West Virginia. EPA monitors recorded a median Air Quality Index of 41 across 154 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 98 (64%) fell in the Good band (AQI 0–50), 56 (36%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 63, while the worst single-day peak hit 81 (Moderate). Residents averaged about 19.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (154 days). Across the 2020–2025 trend window, good days shifted by +11 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 81, moderate but never Unhealthy. Nearby counties show comparable readings: Berkeley (81.1% good, AQI 40); Brooke (79.3% good, AQI 35); Cabell (74.0% good, AQI 41); Greenbrier (89.3% good, AQI 42); Hancock (74.6% good, AQI 42); Harrison (73.3% good, AQI 32).
Air Quality Summary
Good Days
63.6%
98 of 154 monitored days
-11.4pp vs 75% target
Max AQI Recorded
81
Moderate
Health Grade
Moderate
90th-pct AQI 63
Marshall County, Good days share 63.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Marshall 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 154 monitored days across EPA AQI categories.
Good
98
64%
Moderate
56
36%
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 Marshall County.
- PM2.5 · 154 days · 100.0%
Health Impact Assessment
Moderate
Marshall County's air quality is rated Moderate based on 63.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 63.6% of monitored days in 2025, with a median AQI of 41. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 154 of 154 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Marshall County. Best year: 2024 (267 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 87 | 31 | 0 | 0 | 41 | 72 |
| 2021 | 140 | 212 | 1 | 0 | 53 | 121 |
| 2022 | 162 | 199 | 0 | 0 | 52 | 99 |
| 2023 | 149 | 202 | 1 | 1 | 52 | 213 |
| 2024 | 267 | 92 | 0 | 0 | 39 | 81 |
| 2025 | 98 | 56 | 0 | 0 | 41 | 81 |
How does Marshall County compare?
How Marshall County compares
Good-day share worse than US avg
Marshall County 63.6%
Berkeley County, West Virginia 81.1%
US average 76.5%
Median AQI worse than US avg
Marshall County 41
Berkeley County, West Virginia 40
US average 38
Unhealthy days / yr about average
Marshall County 0
Berkeley County, West Virginia 0
US average 0
Other Counties in West Virginia
Air quality comparison for nearby counties in West Virginia.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Marshall County.
Albemarle County, Virginia
AQI 41 · 77.9% good
Anderson County, South Carolina
AQI 41 · 90.0% good
Berkshire County, Massachusetts
AQI 41 · 71.6% good
Berrien County, Michigan
AQI 41 · 80.9% good
Blair County, Pennsylvania
AQI 41 · 71.9% good
Bonner County, Idaho
AQI 41 · 71.3% good
What Marshall 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 41 means for exposure. Health guidance
- See how Marshall County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Marshall County with its West Virginia neighbours before drawing a conclusion about the region. All of West Virginia
Based on 154 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 Marshall County, West Virginia? ▼
Marshall County has a median Air Quality Index (AQI) of 41, rated "Good." 63.6% of monitored days (98 out of 154) had good air quality in 2025.
What is the main pollutant in Marshall County? ▼
The primary pollutant in Marshall County is Fine Particles (PM2.5), which was the main AQI driver on 154 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Marshall County have? ▼
In 2025, Marshall County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 81.
Is the air quality in Marshall County getting better or worse? ▼
Air quality in Marshall County is worsening based on 5-year trends (2020-2025). Best year: 2024 with 267 good days. Worst year: 2020 with 87 good days.
What does AQI 41 mean for health? ▼
Marshall County's median AQI of 41 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 Marshall County compare to other counties in West Virginia? ▼
Marshall County has 63.6% good air days. Nearby counties in West Virginia: Berkeley (81.1% good), Brooke (79.3% good), Cabell (74.0% good), Greenbrier (89.3% good), Hancock (74.6% good), Harrison (73.3% good).
What is the 90th percentile AQI in Marshall County? ▼
The 90th percentile AQI for Marshall County is 63, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 81 (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.