West Virginia · County air quality · 2025
Marshall County, West Virginia
Median AQI 42 (Good). 63.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 63.7%
- Good-air days
- 0
- Unhealthy days
- 20%
- Cleaner than US counties
Marshall County's 2025 annual median AQI is 42 (Good), with 63.7% Good days
According to the U.S. EPA Air Quality System, Marshall County, West Virginia posted a 2025 median AQI of 42 (Good) across 284 monitored days, with 63.7% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Marshall County's 63.7% Good-day share places it cleaner than 20% of US counties in 2025.
- Closest median-AQI peer
- Ada County (74.0% Good, median AQI 42) is the closest nationwide median-AQI peer to Marshall County.
- 2020–2025 trend
- Marshall County's floor-qualifying Good-day share is worsening from 2020 to 2025 (73.7% → 63.7%).
- Median AQI
- Median AQI: 42
According to the 2025 EPA AQS county release on PlainAirData, Marshall County, West Virginia ranks #581 of 951 by median AQI (42) and #757 by good-day share (63.7%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.
Annual release change
What changed in the 2025 EPA annual release
- Marshall County's Good-day share fell from 74.4% to 63.7% between the 2024 and 2025 EPA annual releases, a change of -10.6 percentage points.
- Marshall County's median AQI rose from 39 to 42 between the 2024 and 2025 EPA annual releases, a change of +3 points.
Data updated August 2026
- Good · 181 d · 63.7%
- Moderate · 103 d · 36.3%
How did Marshall County's air break down in 2025?
Across 284 monitored days, 181 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 →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where Marshall County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Marshall County's Good-day share is 63.7% - cleaner than 20% of that comparison set.
Marshall County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
63.7% 20th percentile higher than 20% of 951 US counties
Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Marshall County.
- PM2.5 · 284 days · 100.0%
2024 daily-monitor rhythm in Marshall County
Month-by-month median AQI from EPA day-level county monitors (359 reported days in 2024). Feb posted the highest typical readings (median AQI 56, peak 76); Sep was cleanest at median 31. Summer months (Jun–Aug) averaged median AQI 43 vs 48 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–20241,545 daily readings show a recurring local pattern: Feb has the highest matched-month median AQI (57), while May is lowest (39). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
Marshall County's air quality is rated Moderate based on 63.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 63.7% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 284 of 284 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Marshall County. Highest Good-day share: 2024 (74.4%, 267 of 359 monitored 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 | 181 | 103 | 0 | 0 | 42 | 81 |
How does Marshall County compare?
How Marshall County compares
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Marshall County, West Virginia · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
Every figure on PlainAirData 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.