Median AQI
42
Good
Connecticut · County air quality · 2025
Tolland County, Connecticut
Median AQI 42 (Good). 79.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 79.8%
- Good-air days
- 0
- Unhealthy days
- 52%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Tolland County's air is good on balance, cleaner than the median US county, a median AQI of 42 with 79.8% of 119 monitored days in the Good band, driven mainly by Ozone.
- 42
- median AQI · Good
- 79.8%
- days rated Good
- Ozone
- main pollutant
- 52%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 136.
Data updated July 2026
- Good · 95 d · 79.8%
- Moderate · 21 d · 17.6%
- USG · 3 d · 2.5%
How did Tolland County's air break down in 2025?
Across 119 monitored days, 95 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 136 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 119 days monitored. Median AQI: 42 (Good).
Insights: Tolland County, Connecticut. EPA monitors recorded a median Air Quality Index of 42 across 119 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 95 (80%) fell in the Good band (AQI 0–50), 21 (18%) registered Moderate readings, and 3 (3%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 64, while the worst single-day peak hit 136 (USG). Residents averaged about 23.9 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (119 days). Across the 2020–2025 trend window, good days shifted by -97 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 136, usg but never Unhealthy. Nearby counties show comparable readings: Fairfield (66.8% good, AQI 44); 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).
Air Quality Summary
Good Days
79.8%
95 of 119 monitored days
4.8pp vs 75% target
Max AQI Recorded
136
USG
Health Grade
Good
90th-pct AQI 64
Tolland County, Good days share 79.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Tolland County, Unhealthy-or-worse share 0.0%
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 119 monitored days across EPA AQI categories.
Good
95
80%
Moderate
21
18%
USG
3
3%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Tolland County.
- Ozone · 119 days · 100.0%
Health Impact Assessment
Good
Tolland County's air quality is rated Good based on 79.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 79.8% 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 Ozone, driving AQI on 119 of 119 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Tolland County. Best year: 2020 (192 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 192 | 14 | 0 | 0 | 39 | 93 |
| 2021 | 170 | 30 | 1 | 0 | 39 | 101 |
| 2022 | 187 | 19 | 2 | 0 | 39 | 122 |
| 2023 | 178 | 31 | 2 | 1 | 41 | 156 |
| 2024 | 184 | 16 | 4 | 1 | 37 | 156 |
| 2025 | 95 | 21 | 3 | 0 | 42 | 136 |
How does Tolland County compare?
How Tolland County compares
Good-day share better than US avg
Tolland County 79.8%
Fairfield County, Connecticut 66.8%
US average 76.5%
Median AQI worse than US avg
Tolland County 42
Fairfield County, Connecticut 44
US average 38
Unhealthy days / yr about average
Tolland County 0
Fairfield 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 Tolland County.
Adams County, Pennsylvania
AQI 42 · 73.8% good
Anderson County, Tennessee
AQI 42 · 91.0% good
Andrew County, Missouri
AQI 42 · 84.3% good
Armstrong County, Pennsylvania
AQI 42 · 68.1% good
Baldwin County, Alabama
AQI 42 · 72.2% good
Belmont County, Ohio
AQI 42 · 63.0% good
What Tolland County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 42 means for exposure. Health guidance
- See how Tolland County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Tolland County with its Connecticut neighbours before drawing a conclusion about the region. All of Connecticut
Based on 119 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 Tolland County, Connecticut? ▼
Tolland County has a median Air Quality Index (AQI) of 42, rated "Good." 79.8% of monitored days (95 out of 119) had good air quality in 2025.
What is the main pollutant in Tolland County? ▼
The primary pollutant in Tolland County is Ozone (O3), which was the main AQI driver on 119 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Tolland County have? ▼
In 2025, Tolland County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 136.
Is the air quality in Tolland County getting better or worse? ▼
Air quality in Tolland County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 192 good days. Worst year: 2025 with 95 good days.
What does AQI 42 mean for health? ▼
Tolland County's median AQI of 42 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 Tolland County compare to other counties in Connecticut? ▼
Tolland County has 79.8% good air days. Nearby counties in Connecticut: Fairfield (66.8% good), Hartford (66.8% good), Litchfield (81.8% good), Middlesex (77.9% good), New Haven (68.5% good), New London (79.0% good).
What is the 90th percentile AQI in Tolland County? ▼
The 90th percentile AQI for Tolland County is 64, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 136 (USG).
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.