West Virginia · County air quality · 2025
Marion County, West Virginia
Median AQI 37 (Good). 74.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 74.2%
- Good-air days
- 0
- Unhealthy days
- 43%
- Cleaner than US counties
Marion County's 2025 annual median AQI is 37 (Good), with 74.2% Good days
According to the U.S. EPA Air Quality System, Marion County, West Virginia posted a 2025 median AQI of 37 (Good) across 120 monitored days, with 74.2% 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
- Marion County's 74.2% Good-day share places it cleaner than 43% of US counties in 2025.
- Closest median-AQI peer
- Alachua County (88.7% Good, median AQI 37) is the closest nationwide median-AQI peer to Marion County.
- 2022–2025 trend
- Marion County's floor-qualifying Good-day share is worsening from 2022 to 2025 (77.8% → 74.2%).
- Median AQI
- Median AQI: 37
According to the 2025 EPA AQS county release on PlainAirData, Marion County, West Virginia ranks #286 of 951 by median AQI (37) and #546 by good-day share (74.2%). 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
- Marion County's Good-day share fell from 76.6% to 74.2% between the 2024 and 2025 EPA annual releases, a change of -2.4 percentage points.
- Marion County's median AQI rose from 33 to 37 between the 2024 and 2025 EPA annual releases, a change of +4 points.
Data updated August 2026
- Good · 89 d · 74.2%
- Moderate · 31 d · 25.8%
How did Marion County's air break down in 2025?
Across 120 monitored days, 89 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 71 (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 Marion County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Marion County's Good-day share is 74.2% - cleaner than 43% of that comparison set.
Marion County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
74.2% 43rd percentile higher than 43% 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 Marion County.
- PM2.5 · 120 days · 100.0%
2024 daily-monitor rhythm in Marion County
Month-by-month median AQI from EPA day-level county monitors (111 reported days in 2024). Jul posted the highest typical readings (median AQI 52, peak 57); Sep was cleanest at median 21. Summer months (Jun–Aug) averaged median AQI 47 vs 33 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–2024511 daily readings show a recurring local pattern: Jul has the highest matched-month median AQI (51), while Oct is lowest (29). 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
Marion County's air quality is rated Moderate based on 74.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 74.2% 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 PM2.5, driving AQI on 120 of 120 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Marion County. Highest Good-day share: 2022 (77.8%, 91 of 117 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 57 | 17 | 0 | 0 | 35 | 70 |
| 2021 | 61 | 30 | 0 | 0 | 40 | 82 |
| 2022 | 91 | 26 | 0 | 0 | 36 | 73 |
| 2023 | 84 | 33 | 0 | 1 | 39 | 170 |
| 2024 | 85 | 26 | 0 | 0 | 33 | 62 |
| 2025 | 89 | 31 | 0 | 0 | 37 | 71 |
How does Marion County compare?
How Marion 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 Marion 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.