Metro area air quality · 2025

Norwich-New London, CT

Median AQI 38 (Good). 81.3% of monitored days rated Good across this metro's EPA monitoring network.

38
Median AQI
81.3%
Good-air days
0
Unhealthy days
70%
Cleaner than US metros

Norwich-New London, CT posted a 2025 median AQI of 38 (Good) with 81.3% Good days

According to the U.S. EPA Air Quality System, the Norwich-New London, CT CBSA recorded a median AQI of 38 across 364 monitored days in 2025, with 81.3% rated Good and 0 unhealthy or worse. This is an annual metro comparison, not a live advisory.

Data source EPA Air Quality System (AQS)

Cleaner than US metros
The Norwich-New London, CT CBSA's 81.3% Good-day share places it cleaner than 70% of US metros in 2025.
Closest median-AQI peer
Appleton, WI (72.3% Good, median AQI 38) is the closest nationwide median-AQI peer to Norwich-New London, CT.
2020–2025 Good-day shift
Norwich-New London, CT's Good-day share moved +7.5 points from 2020 to 2025 (median AQI -3).
Median AQI
Median AQI: 38

Aggregated from EPA Air Quality System (2025), 364 monitored days. EPA AQS →

The verdict

Norwich-New London, CT sits in the upper Good-day tercile among EPA CBSA metros on this site (81.3% of 364 monitored days). On the EPA scale the metro runs good, cleaner than the median US metro, with a median AQI of 38 and 81.3% of 364 monitored days in the Good band.

38
median AQI · Good
81.3%
days rated Good
70%
cleaner than US metros
136
worst single reading

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

Annual release change

What changed in the 2025 EPA annual release

2024 → 2025
  • Norwich-New London, CT metro's Good-day share fell from 85.8% to 83.1% between the 2024 and 2025 EPA annual releases, a change of -2.7 percentage points.
  • Norwich-New London, CT metro's peak single-day AQI rose from 126 to 136 between the 2024 and 2025 EPA annual releases, a change of +10 points.

Compared against 360 monitored days in 2024 and 356 in 2025. These are arithmetic differences between two stored EPA annual summaries, not a cause claim or a live advisory.

National release changes Two-year CSV

Norwich-New London, CT sits in the upper Good-day tercile among EPA CBSA metros on this site (81.3% of 364 monitored days). Signature read: 81.3% Good-day share (high tercile vs CBSA corpus). Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 38 over 364 measured days in 2025 (Good / Good). The monitored-day split lands at 296 Good (81%), 60 Moderate (16%), and 8 Unhealthy-for-Sensitive-Groups (2%). The 90th-percentile AQI finished at 60; the highest single-day reading hit 136 (USG).

Across 2020–2025, Good-day share shifted +7.5 points and median AQI moved -3 (improving). No Unhealthy-tier days appear in this annual dataset. Metros with comparable AQI profiles include Appleton, WI (72.3% good, AQI 38); Billings, MT (86.3% good, AQI 38); Burlington-South Burlington, VT (87.7% good, AQI 38).

Health effects of air pollution →

Air Quality Summary

Median AQI

38

Good

Good Days

81.3%

296 of 364 days

Max AQI

136

USG

Health Grade

Good

90th pct: 60

AQI Day Breakdown (2025)

Distribution of 364 monitored days across EPA AQI categories.

Good

296

81%

Moderate

60

16%

USG

8

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 81.3% 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 typical
Norwich-New London, CT 81.3%
Appleton, WI 72.3%
Typical US metro 70.6%
Median AQI better than typical
Norwich-New London, CT 38
Appleton, WI 38
Typical US metro 41
Unhealthy days / yr better than typical
Norwich-New London, CT 0
Appleton, WI 6
Typical US metro 1

5-Year Air Quality Trend

Air quality is improving in the Norwich-New London, CT metro. Highest Good-day share: 2024 (85.8%, 309 of 360 monitored 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 296 60 0 38

Metros with a similar median AQI

CBSA peers nationwide whose annual median AQI sits near Norwich-New London, CT (38).

Appleton, WI

Median AQI 38 · 72.3% Good-day share

38

Billings, MT

Median AQI 38 · 86.3% Good-day share

38

Burlington-South Burlington, VT

Median AQI 38 · 87.7% Good-day share

38

Charlottesville, VA

Median AQI 38 · 81.0% Good-day share

38

Corning, NY

Median AQI 38 · 83.3% Good-day share

38

Dickinson, ND

Median AQI 38 · 82.7% Good-day share

38

Metros with similar unhealthy-day exposure

A second relationship type: metros whose unhealthy-or-worse day count is closest to Norwich-New London, CT's 0 (independent of median AQI).

Aberdeen, SD

0 unhealthy-or-worse days · median AQI 27

27

Aberdeen, WA

0 unhealthy-or-worse days · median AQI 22

22

Adrian, MI

0 unhealthy-or-worse days · median AQI 41

41

Akron, OH

0 unhealthy-or-worse days · median AQI 45

45

Albany, GA

0 unhealthy-or-worse days · median AQI 46

46

Albany, OR

0 unhealthy-or-worse days · median AQI 27

27

Frequently Asked Questions

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.
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 38, rated "Good." 81.3% of monitored days (296 out of 364) had good air quality in 2025.
Is air quality in Norwich-New London, CT getting better or worse? ▼
Air quality in the Norwich-New London, CT metro is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2024 at 85.8% (309 of 360 days). Lowest qualifying Good-day share: 2023 at 72.5% (258 of 356 days).
What does AQI 38 mean for health? ▼
An AQI of 38 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
How does Norwich-New London, CT compare to other metro areas? ▼
The Norwich-New London, CT metro has 81.3% good air days. Similar metros: Appleton, WI (72.3% good), Billings, MT (86.3% good), Burlington-South Burlington, VT (87.7% good).
What is the 90th percentile AQI for Norwich-New London, CT? ▼
The 90th percentile AQI for the Norwich-New London, CT metro area is 60, 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 CBSA dataset for Norwich-New London, CT, 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, Norwich-New London, CT · 2020–2025