Metro area air quality · 2025

Norwich-New London, CT

Median AQI 40 (Good). 79.0% of monitored days rated Good across this metro's EPA monitoring network.

40
Median AQI
79.0%
Good-air days
0
Unhealthy days
60%
Cleaner than US metros

Aggregated from EPA Air Quality System (2025), 181 monitored days. EPA AQS →

The verdict

The Norwich-New London, CT metro runs good on the EPA scale, cleaner than the median US metro, a median AQI of 40 with 79.0% of 181 monitored days in the Good band.

40
median AQI · Good
79.0%
days rated Good
60%
cleaner than US metros
136
worst single reading

No day crossed into the Unhealthy tier across the metro's monitors in 2025.

Insights: Norwich-New London, CT metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 40 over 181 measured days in 2025, which corresponds to a Good band and a Good metro-wide health grade. The monitored-day split lands at 143 Good days (79%), 34 Moderate (19%), and 4 Unhealthy-for-Sensitive-Groups (2%). The 90th-percentile AQI finished at 59 while the highest single-day reading hit 136 (USG). Metro residents averaged roughly 23.7 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by -131 and the median AQI moved -1 points, which classifies the multi-year trajectory as improving. The metro avoided any Unhealthy-tier days entirely, an outcome that typically reflects favorable wind patterns, lower industrial density, or effective regional emission controls. Metros with comparable AQI profiles include Berlin, NH-VT (85.4% good, AQI 40); Burlington-South Burlington, VT (91.2% good, AQI 40); Cambridge, MD (84.4% good, AQI 40).

Air Quality Summary

Median AQI

40

Good

Good Days

79.0%

143 of 181 days

Max AQI

136

USG

Health Grade

Good

90th pct: 59

AQI Day Breakdown (2025)

Distribution of 181 monitored days across EPA AQI categories.

Good

143

79%

Moderate

34

19%

USG

4

2%

Unhealthy

0

0%

Very Unhealthy

0

0%

Hazardous

0

0%

Health Impact Assessment

Good

The Norwich-New London, CT metro area's air quality is rated Good based on 79.0% good air days. No unhealthy air days were recorded in 2025.

Air quality is generally acceptable. Unusually sensitive people should monitor real-time conditions at AirNow.gov during high-pollution events.

How does the Norwich-New London, CT metro compare?

How Norwich-New London, CT compares

Good-day share better than US avg
Norwich-New London, CT 79.0%
Berlin, NH-VT 85.4%
US average 71.3%
Median AQI better than US avg
Norwich-New London, CT 40
Berlin, NH-VT 40
US average 41
Unhealthy days / yr better than US avg
Norwich-New London, CT 0
Berlin, NH-VT 0
US average 1

5-Year Air Quality Trend

Air quality is improving in the Norwich-New London, CT metro. Best year: 2024 (309 good days).

Year Good Moderate Unhealthy Median AQI
2020 274 87 1 41
2021 277 79 0 39
2022 290 71 0 39
2023 258 95 3 41
2024 309 51 0 37
2025 143 34 0 40

Metros with Similar Air Quality

Metro areas across the US with a similar median AQI to Norwich-New London, CT.

Berlin, NH-VT

AQI 40 · 85.4% good

40

Burlington-South Burlington, VT

AQI 40 · 91.2% good

40

Cambridge, MD

AQI 40 · 84.4% good

40

Charleston, WV

AQI 40 · 79.6% good

40

Corning, NY

AQI 40 · 80.2% good

40

Dickinson, ND

AQI 40 · 80.3% good

40

More Air Quality Data

Explore EPA air quality rankings and guides across U.S. metros and counties.

Cleanest Metro Areas

U.S. metros ranked by their share of Good air-quality days.

Worst Air Quality

Counties and metros with the most unhealthy air days.

All Metro Areas

Annual AQI by CBSA for every monitored U.S. metro area.

Best and Worst City Air

What drives urban air quality and how metro areas compare.

Air Quality Guides

Frequently Asked Questions

What is the air quality in the Norwich-New London, CT metro area? ▼
The Norwich-New London, CT metro area has a median Air Quality Index (AQI) of 40, rated "Good." 79.0% of monitored days (143 out of 181) had good air quality in 2025.
How many unhealthy air days does Norwich-New London, CT have? ▼
In 2025, the Norwich-New London, CT metro area recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 136.
Is air quality in Norwich-New London, CT getting better or worse? ▼
Air quality in the Norwich-New London, CT metro is improving based on 5-year trends (2020-2025). Best year: 2024 with 309 good days. Worst year: 2025 with 143 good days.
What does AQI 40 mean for health? ▼
An AQI of 40 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
What is the 90th percentile AQI for Norwich-New London, CT? ▼
The 90th percentile AQI for the Norwich-New London, CT metro area is 59, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 136 (USG).
How does Norwich-New London, CT compare to other metro areas? ▼
The Norwich-New London, CT metro has 79.0% good air days. Similar metros: Berlin, NH-VT (85.4% good), Burlington-South Burlington, VT (91.2% good), Cambridge, MD (84.4% good).

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset, 2020–2025. See our methodology for how AQI, median, and coverage figures are computed.

Read our methodology , how this data is sourced, computed, and verified.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by CBSA summary files (metro-level) · 2020–2025

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.