Connecticut · County air quality · 2025
Windham County, Connecticut
Median AQI 35 (Good). 93.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 35
- Median AQI
- 93.7%
- Good-air days
- 0
- Unhealthy days
- 89%
- Cleaner than US counties
Windham County's 2025 annual median AQI is 35 (Good), with 93.7% Good days
According to the U.S. EPA Air Quality System, Windham County, Connecticut posted a 2025 median AQI of 35 (Good) across 362 monitored days, with 93.7% 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
- Windham County's 93.7% Good-day share places it cleaner than 89% of US counties in 2025.
- Closest median-AQI peer
- Atascosa County (76.0% Good, median AQI 35) is the closest nationwide median-AQI peer to Windham County.
- 2020–2025 trend
- Windham County's floor-qualifying Good-day share is worsening from 2020 to 2025 (96.9% → 93.6%).
- Median AQI
- Median AQI: 35
According to the 2025 EPA AQS county release on PlainAirData, Windham County, Connecticut ranks #191 of 951 by median AQI (35) and #109 by good-day share (93.7%). 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
- Windham County's peak single-day AQI fell from 122 to 108 between the 2024 and 2025 EPA annual releases, a change of -14 points.
- Windham County's Good-day share fell from 94.7% to 93.6% between the 2024 and 2025 EPA annual releases, a change of -1.1 percentage points.
Data updated August 2026
- Good · 339 d · 93.6%
- Moderate · 22 d · 6.1%
- USG · 1 d · 0.3%
How did Windham County's air break down in 2025?
Across 362 monitored days, 339 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
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 Windham County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Windham County's Good-day share is 93.7% - cleaner than 89% of that comparison set.
Windham County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
93.7% Cleaner than 89% higher than 89% 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 Windham County.
- Ozone · 362 days · 100.0%
2024 daily-monitor rhythm in Windham County
Month-by-month median AQI from EPA day-level county monitors (359 reported days in 2024). Jun posted the highest typical readings (median AQI 41, peak 122); Dec was cleanest at median 28. Summer months (Jun–Aug) averaged median AQI 37 vs 32 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–20241,790 daily readings show a recurring local pattern: Apr has the highest matched-month median AQI (41), while Dec 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
Windham County's air quality is rated Excellent based on 93.7% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 93.7% of monitored days in 2025, with a median AQI of 35. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 362 of 362 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Windham County. Highest Good-day share: 2020 (96.9%, 345 of 356 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 345 | 11 | 0 | 0 | 35 | 87 |
| 2021 | 331 | 29 | 1 | 0 | 34 | 140 |
| 2022 | 338 | 17 | 0 | 0 | 35 | 93 |
| 2023 | 340 | 17 | 2 | 0 | 34 | 112 |
| 2024 | 340 | 17 | 2 | 0 | 34 | 122 |
| 2025 | 339 | 22 | 1 | 0 | 35 | 108 |
How does Windham County compare?
How Windham 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 Windham County, Connecticut · 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.