Median AQI
44
Good
Connecticut · County air quality · 2025
Fairfield County, Connecticut
Median AQI 44 (Good). 66.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 66.8%
- Good-air days
- 1
- Unhealthy days
- 26%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Fairfield County's air is good on balance, more polluted than the median US county, a median AQI of 44 with 66.8% of 181 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 66.8%
- days rated Good
- Ozone
- main pollutant
- 26%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 166.
Data updated July 2026
- Good · 121 d · 66.9%
- Moderate · 51 d · 28.2%
- USG · 8 d · 4.4%
- Unhealthy · 1 d · 0.6%
How did Fairfield County's air break down in 2025?
Across 181 monitored days, 121 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 166 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 44 (Good).
Insights: Fairfield County, Connecticut. EPA monitors recorded a median Air Quality Index of 44 across 181 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 121 (67%) fell in the Good band (AQI 0–50), 51 (28%) registered Moderate readings, and 8 (4%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 69, while the worst single-day peak hit 166 (Unhealthy). Residents averaged about 20.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (98 days), PM2.5 (71 days), NO2 (12 days). Across the 2020–2025 trend window, good days shifted by -96 and the median AQI moved -3 points, placing the multi-year trajectory at improving. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Hartford (66.8% good, AQI 44); Litchfield (81.8% good, AQI 41); Middlesex (77.9% good, AQI 42); New Haven (68.5% good, AQI 44); New London (79.0% good, AQI 40); Tolland (79.8% good, AQI 42).
Air Quality Summary
Good Days
66.8%
121 of 181 monitored days
-8.2pp vs 75% target
Max AQI Recorded
166
Unhealthy
Health Grade
Moderate
90th-pct AQI 69
Fairfield County, Good days share 66.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Fairfield County, Unhealthy-or-worse share 0.6%
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 181 monitored days across EPA AQI categories.
Good
121
67%
Moderate
51
28%
USG
8
4%
Unhealthy
1
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Fairfield County.
- Ozone · 98 days · 54.1%
- PM2.5 · 71 days · 39.2%
- NO₂ · 12 days · 6.6%
Health Impact Assessment
Moderate
Fairfield County's air quality is rated Moderate based on 66.8% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 8 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 166. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is Ozone, driving AQI on 98 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Fairfield County. Best year: 2024 (248 good 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 | 121 | 51 | 8 | 1 | 44 | 166 |
How does Fairfield County compare?
How Fairfield County compares
Good-day share worse than US avg
Fairfield County 66.8%
Hartford County, Connecticut 66.8%
US average 76.5%
Median AQI worse than US avg
Fairfield County 44
Hartford County, Connecticut 44
US average 38
Unhealthy days / yr worse than US avg
Fairfield County 1
Hartford County, Connecticut 1
US average 0
Other Counties in Connecticut
Air quality comparison for nearby counties in Connecticut.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Fairfield County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Fairfield County's air means for you
On most days the air here is fine, but Ozone drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 44 means for exposure. Health guidance
- See how Fairfield County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Fairfield County with its Connecticut neighbours before drawing a conclusion about the region. All of Connecticut
Based on 181 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 Fairfield County, Connecticut? ▼
Fairfield County has a median Air Quality Index (AQI) of 44, rated "Good." 66.8% of monitored days (121 out of 181) had good air quality in 2025.
What is the main pollutant in Fairfield County? ▼
The primary pollutant in Fairfield County is Ozone (O3), which was the main AQI driver on 98 days (54% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Fairfield County have? ▼
In 2025, Fairfield County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 166.
Is the air quality in Fairfield County getting better or worse? ▼
Air quality in Fairfield County is improving based on 5-year trends (2020-2025). Best year: 2024 with 248 good days. Worst year: 2025 with 121 good days.
What does AQI 44 mean for health? ▼
Fairfield County's median AQI of 44 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 Fairfield County compare to other counties in Connecticut? ▼
Fairfield County has 66.8% good air days. Nearby counties in Connecticut: Hartford (66.8% good), Litchfield (81.8% good), Middlesex (77.9% good), New Haven (68.5% good), New London (79.0% good), Tolland (79.8% good).
What is the 90th percentile AQI in Fairfield County? ▼
The 90th percentile AQI for Fairfield County is 69, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 166 (Unhealthy).
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.