Connecticut · County air quality · 2025
Fairfield County, Connecticut
Median AQI 44 (Good). 64.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 64.7%
- Good-air days
- 2
- Unhealthy days
- 22%
- Cleaner than US counties
Fairfield County's 2025 annual median AQI is 44 (Good), with 64.7% Good days
According to the U.S. EPA Air Quality System, Fairfield County, Connecticut posted a 2025 median AQI of 44 (Good) across 365 monitored days, with 64.7% rated Good and 2 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Fairfield County's 64.7% Good-day share places it cleaner than 22% of US counties in 2025.
- Closest median-AQI peer
- Allegan County (63.9% Good, median AQI 44) is the closest nationwide median-AQI peer to Fairfield County.
- 2020–2025 trend
- Fairfield County's floor-qualifying Good-day share is improving from 2020 to 2025 (59.3% → 64.7%).
- Median AQI
- Median AQI: 44
According to the 2025 EPA AQS county release on PlainAirData, Fairfield County, Connecticut ranks #680 of 951 by median AQI (44) and #736 by good-day share (64.7%). 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
- Fairfield County's Good-day share fell from 67.8% to 64.7% between the 2024 and 2025 EPA annual releases, a change of -3.1 percentage points.
- Fairfield County's peak single-day AQI rose from 154 to 174 between the 2024 and 2025 EPA annual releases, a change of +20 points.
- Fairfield County's Unhealthy-category days fell from 3 to 2 between the 2024 and 2025 EPA annual releases, a change of -1 days.
Data updated August 2026
- Good · 236 d · 64.7%
- Moderate · 108 d · 29.6%
- USG · 19 d · 5.2%
- Unhealthy · 2 d · 0.5%
How did Fairfield County's air break down in 2025?
Across 365 monitored days, 236 fell in the Good band (AQI 0–50) and 2 reached Unhealthy or worse. The worst single day peaked at AQI 174 (Unhealthy).
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 Fairfield County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Fairfield County's Good-day share is 64.7% - cleaner than 22% of that comparison set.
Fairfield County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
64.7% 22nd percentile higher than 22% 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 Fairfield County.
- PM2.5 · 170 days · 46.6%
- Ozone · 169 days · 46.3%
- NO₂ · 26 days · 7.1%
2024 daily-monitor rhythm in Fairfield County
Month-by-month median AQI from EPA day-level county monitors (366 reported days in 2024). Aug posted the highest typical readings (median AQI 63, peak 140); Jan was cleanest at median 30. Summer months (Jun–Aug) averaged median AQI 60 vs 36 in Dec–Feb. 3 days crossed Unhealthy (AQI >150) at least once that year.
Five-year seasonal record
EPA day-level county files · 2020–20241,825 daily readings show a recurring local pattern: Jul has the highest matched-month median AQI (65), while Oct is lowest (36). 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
Fairfield County's air quality is rated Moderate based on 64.7% good air days. There were 2 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 19 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 174. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 170 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Fairfield County. Highest Good-day share: 2024 (67.8%, 248 of 366 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 217 | 136 | 12 | 1 | 47 | 161 |
| 2021 | 225 | 119 | 13 | 6 | 46 | 185 |
| 2022 | 223 | 120 | 20 | 2 | 45 | 156 |
| 2023 | 210 | 135 | 12 | 7 | 46 | 242 |
| 2024 | 248 | 97 | 18 | 3 | 42 | 154 |
| 2025 | 236 | 108 | 19 | 2 | 44 | 174 |
How does Fairfield County compare?
How Fairfield 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 Fairfield 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.