Metro area air quality · 2025

Portland-South Portland, ME

Median AQI 41 (Good). 73.7% of monitored days rated Good across this metro's EPA monitoring network.

41
Median AQI
73.7%
Good-air days
1
Unhealthy days
51%
Cleaner than US metros

Aggregated from EPA Air Quality System (2025), 304 monitored days. EPA AQS →

The verdict

The Portland-South Portland, ME metro runs good on the EPA scale, cleaner than the median US metro, a median AQI of 41 with 73.7% of 304 monitored days in the Good band.

41
median AQI · Good
73.7%
days rated Good
51%
cleaner than US metros
169
worst single reading

1 day reached Unhealthy or worse across the metro's monitors in 2025.

Insights: Portland-South Portland, ME metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 41 over 304 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 224 Good days (74%), 74 Moderate (24%), and 5 Unhealthy-for-Sensitive-Groups (2%). The 90th-percentile AQI finished at 64 while the highest single-day reading hit 169 (Unhealthy). Metro residents averaged roughly 22.1 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by -38 and the median AQI moved -1 points, which classifies the multi-year trajectory as improving. The metro recorded 1 unhealthy-or-worse days combined, on those days the EPA recommends that sensitive groups limit prolonged outdoor exertion, and many schools and athletic programs adjust outdoor activity accordingly. Metros with comparable AQI profiles include Adrian, MI (77.3% good, AQI 41); Altoona, PA (71.9% good, AQI 41); Ann Arbor, MI (76.0% good, AQI 41).

Air Quality Summary

Median AQI

41

Good

Good Days

73.7%

224 of 304 days

Max AQI

169

Unhealthy

Health Grade

Moderate

90th pct: 64

AQI Day Breakdown (2025)

Distribution of 304 monitored days across EPA AQI categories.

Good

224

74%

Moderate

74

24%

USG

5

2%

Unhealthy

1

0%

Very Unhealthy

0

0%

Hazardous

0

0%

Health Impact Assessment

Moderate

The Portland-South Portland, ME metro area's air quality is rated Moderate based on 73.7% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.

Air quality is acceptable most days, but 5 days reached "Unhealthy for Sensitive Groups" and peak AQI reached 169. Sensitive groups should monitor real-time conditions at AirNow.gov.

How does the Portland-South Portland, ME metro compare?

How Portland-South Portland, ME compares

Good-day share better than US avg
Portland-South Portland, ME 73.7%
Adrian, MI 77.3%
US average 71.3%
Median AQI about average
Portland-South Portland, ME 41
Adrian, MI 41
US average 41
Unhealthy days / yr about average
Portland-South Portland, ME 1
Adrian, MI 0
US average 1

5-Year Air Quality Trend

Air quality is improving in the Portland-South Portland, ME metro. Best year: 2022 (320 good days).

Year Good Moderate Unhealthy Median AQI
2020 262 104 0 42
2021 313 49 0 36
2022 320 39 0 37
2023 261 101 0 41
2024 289 76 0 39
2025 224 74 1 41

Metros with Similar Air Quality

Metro areas across the US with a similar median AQI to Portland-South Portland, ME.

Adrian, MI

AQI 41 · 77.3% good

41

Altoona, PA

AQI 41 · 71.9% good

41

Ann Arbor, MI

AQI 41 · 76.0% good

41

Bowling Green, KY

AQI 41 · 81.2% good

41

Charlottesville, VA

AQI 41 · 77.9% good

41

Clarksville, TN-KY

AQI 41 · 76.8% good

41

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 Portland-South Portland, ME metro area? ▼
The Portland-South Portland, ME metro area has a median Air Quality Index (AQI) of 41, rated "Good." 73.7% of monitored days (224 out of 304) had good air quality in 2025.
How many unhealthy air days does Portland-South Portland, ME have? ▼
In 2025, the Portland-South Portland, ME metro area recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 169.
Is air quality in Portland-South Portland, ME getting better or worse? ▼
Air quality in the Portland-South Portland, ME metro is improving based on 5-year trends (2020-2025). Best year: 2022 with 320 good days. Worst year: 2025 with 224 good days.
What does AQI 41 mean for health? ▼
An AQI of 41 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 Portland-South Portland, ME? ▼
The 90th percentile AQI for the Portland-South Portland, ME metro area is 64, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 169 (Unhealthy).
How does Portland-South Portland, ME compare to other metro areas? ▼
The Portland-South Portland, ME metro has 73.7% good air days. Similar metros: Adrian, MI (77.3% good), Altoona, PA (71.9% good), Ann Arbor, MI (76.0% 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

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.