Metro area air quality · 2025

Worcester, MA-CT

Median AQI 39 (Good). 81.1% of monitored days rated Good across this metro's EPA monitoring network.

39
Median AQI
81.1%
Good-air days
0
Unhealthy days
69%
Cleaner than US metros

Worcester, MA-CT posted a 2025 median AQI of 39 (Good) with 81.1% Good days

According to the U.S. EPA Air Quality System, the Worcester, MA-CT CBSA recorded a median AQI of 39 across 365 monitored days in 2025, with 81.1% 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 Worcester, MA-CT CBSA's 81.1% Good-day share places it cleaner than 69% of US metros in 2025.
Closest median-AQI peer
Bay City, MI (70.4% Good, median AQI 39) is the closest nationwide median-AQI peer to Worcester, MA-CT.
2020–2025 Good-day shift
Worcester, MA-CT's Good-day share moved +11.4 points from 2020 to 2025 (median AQI -4).
Median AQI
Median AQI: 39

Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →

The verdict

The Worcester, MA-CT metro runs good on the EPA scale, cleaner than the median US metro, a median AQI of 39 with 81.1% of 365 monitored days in the Good band.

39
median AQI · Good
81.1%
days rated Good
69%
cleaner than US metros
108
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
  • Worcester, MA-CT metro's Good-day share fell from 87.1% to 81.3% between the 2024 and 2025 EPA annual releases, a change of -5.8 percentage points.
  • Worcester, MA-CT metro's peak single-day AQI fell from 122 to 108 between the 2024 and 2025 EPA annual releases, a change of -14 points.

Compared against 364 monitored days in 2024 and 364 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

Insights: Worcester, MA-CT metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 39 over 365 measured days in 2025, which corresponds to a Good band and a Good metro-wide health grade. The monitored-day split lands at 296 Good days (81%), 68 Moderate (19%), and 1 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 59 while the highest single-day reading hit 108 (USG). Metro residents averaged roughly 24.3 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +11.4 points and the median AQI moved -4 points, which classifies the multi-year trajectory as improving. The metro recorded no Unhealthy-tier days in this annual dataset. Metros with comparable AQI profiles include Bay City, MI (70.4% good, AQI 39); Brainerd, MN (74.3% good, AQI 39); Cambridge, MD (86.0% good, AQI 39).

Air Quality Summary

Median AQI

39

Good

Good Days

81.1%

296 of 365 days

Max AQI

108

USG

Health Grade

Good

90th pct: 59

AQI Day Breakdown (2025)

Distribution of 365 monitored days across EPA AQI categories.

Good

296

81%

Moderate

68

19%

USG

1

0%

Unhealthy

0

0%

Very Unhealthy

0

0%

Hazardous

0

0%

Health Impact Assessment

Good

The Worcester, MA-CT metro area's air quality is rated Good based on 81.1% 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 Worcester, MA-CT metro compare?

How Worcester, MA-CT compares

Good-day share better than typical
Worcester, MA-CT 81.1%
Bay City, MI 70.4%
Typical US metro 70.6%
Median AQI better than typical
Worcester, MA-CT 39
Bay City, MI 39
Typical US metro 41
Unhealthy days / yr better than typical
Worcester, MA-CT 0
Bay City, MI 0
Typical US metro 1

5-Year Air Quality Trend

Air quality is improving in the Worcester, MA-CT metro. Highest Good-day share: 2024 (87.1%, 317 of 364 monitored days).

Year Good Moderate Unhealthy Median AQI
2020 256 110 0 43
2021 216 146 0 45
2022 227 138 0 46
2023 265 96 0 40
2024 317 47 0 37
2025 296 68 0 39

Metros with a similar median AQI

CBSA peers nationwide whose annual median AQI sits near Worcester, MA-CT (39).

Bay City, MI

Median AQI 39 · 70.4% Good-day share

39

Brainerd, MN

Median AQI 39 · 74.3% Good-day share

39

Cambridge, MD

Median AQI 39 · 86.0% Good-day share

39

Charleston, WV

Median AQI 39 · 77.0% Good-day share

39

Dalton, GA

Median AQI 39 · 90.3% Good-day share

39

Harrisonburg, VA

Median AQI 39 · 80.0% Good-day share

39

Metros with similar unhealthy-day exposure

A second relationship type: metros whose unhealthy-or-worse day count is closest to Worcester, MA-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

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 Worcester, MA-CT metro area? ▼
The Worcester, MA-CT metro area has a median Air Quality Index (AQI) of 39, rated "Good." 81.1% of monitored days (296 out of 365) had good air quality in 2025.
How many unhealthy air days does Worcester, MA-CT have? ▼
In 2025, the Worcester, MA-CT metro area recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 108.
Is air quality in Worcester, MA-CT getting better or worse? ▼
Air quality in the Worcester, MA-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 87.1% (317 of 364 days). Lowest qualifying Good-day share: 2021 at 59.7% (216 of 362 days).
What does AQI 39 mean for health? ▼
An AQI of 39 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 Worcester, MA-CT? ▼
The 90th percentile AQI for the Worcester, MA-CT metro area is 59, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 108 (USG).
How does Worcester, MA-CT compare to other metro areas? ▼
The Worcester, MA-CT metro has 81.1% good air days. Similar metros: Bay City, MI (70.4% good), Brainerd, MN (74.3% good), Cambridge, MD (86.0% 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

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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.