State air quality · 2025

Maine Air Quality Ranking

Across 11 monitored counties, the typical county in Maine posts a median AQI of 35 (Good) and 87.0% of monitored days were rated Good, from EPA AQS.

35
Avg median AQI
87.0%
Good-air days
11
Counties monitored
96%
Cleaner than US states

Maine's typical county median AQI is 35 (Good) across 11 monitored counties

According to the U.S. EPA Air Quality System, Maine monitors 11 counties with a day-weighted Good-day share of 87.0%. Cleanest: Knox County (97.8% Good). Most polluted: Cumberland County (74.3%). These are annual summaries, not live AirNow readings.

Data source EPA Air Quality System (AQS)

Cleaner than US states
Maine's day-weighted Good-day share of 87.0% places it cleaner than 96% of US states.
In-state spread
Within Maine, Knox County leads at 97.8% Good days while Cumberland County sits at 74.3% across 11 monitored counties.
2024→2025 release
Maine's Good-day share moved -3.1 points vs the 2024 EPA annual release.
Typical median AQI
Typical median AQI: 35

Verify with AirNow → · EPA AQS →

EPA state monitoring brief

AQS state key MAINE

Maine · 2025 EPA AQS · 11 counties · med AQI 35 · 87.0% Good · Knox→Cumberland spread

  • GOOD 35 Median AQI · Good
  • SHARE 87.0% Good-day share
  • COUNT 11 Counties monitored
  • UNH 2 Unhealthy+ days
  • RANK 96% Cleaner than states
  • O3 66.2% Main pollutant share

Good-day share peers

Maine (this)87%Virginia86.5%Montana85.9%Wyoming85.1%
Good-day share neighbourhood · nearest ABS peers vs Maine

Maine's 87.0% Good-day share is cleaner than 96% of monitored US states; Knox and Cumberland County bracket the in-state range. Open Knox County →

According to EPA AQS annual summaries on PlainAirData, Maine ranks #2 of 52 by day-weighted good-day share (87.0%) and #12 by mean county median AQI (34.6). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).

Data updated August 2026

What changed, what drives it, and how thick is the sample

Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.

Release change

87.0%

Good-day share in 2025, down 3.1 percentage points vs 2024. County-mean median AQI 35, within half a point of the 2024 county-mean median.

Pollutant mix

Ozone

Main driver on 66.2% of pollutant-assigned days.

  • Ozone 66.2%
  • PM2.5 33.0%
  • PM10 0.9%

Monitoring coverage

350

Average monitored days per county in the latest release. Every monitored county clears the 100-day ranking floor.

Counties Monitored

11

Good Days %

87.0%

Avg Median AQI

35

Total Unhealthy Days

2

Best Air Quality

Knox County

Worst Air Quality

Cumberland County

Where Maine sits nationally

COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Maine's day-weighted Good-day share is 87.0% - cleaner than 96% of that comparison set.

Maine Good-day share vs. every US state

Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

87.0% Cleaner than 96% higher than 96% of 52 US states

0.0%–5.0%: 0 US states (0%). Below this entry. 5.0%–10.0%: 0 US states (0%). Below this entry. 10.0%–15.0%: 0 US states (0%). Below this entry. 15.0%–20.0%: 0 US states (0%). Below this entry. 20.0%–25.0%: 0 US states (0%). Below this entry. 25.0%–30.0%: 0 US states (0%). Below this entry. 30.0%–35.0%: 0 US states (0%). Below this entry. 35.0%–40.0%: 0 US states (0%). Below this entry. 40.0%–45.0%: 0 US states (0%). Below this entry. 45.0%–50.0%: 0 US states (0%). Below this entry. 50.0%–55.0%: 0 US states (0%). Below this entry. 55.0%–60.0%: 0 US states (0%). Below this entry. 60.0%–65.0%: 2 US states (4%). Below this entry. 65.0%–70.0%: 9 US states (17%). Below this entry. 70.0%–75.0%: 11 US states (21%). Below this entry. 75.0%–80.0%: 11 US states (21%). Below this entry. 80.0%–85.0%: 13 US states (25%). Below this entry. 85.0%–90.0%: 5 US states (10%). This entry sits in this band. 90.0%–95.0%: 1 US states (2%). Above this entry. 95.0%–100.0%: 0 US states (0%). Above this entry. 100.0%–105.0%: 0 US states (0%). Above this entry. This state 0.0% 100% every floor-qualified US state, bucketed by value

Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.

Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025

Which counties in Maine have the cleanest and most polluted air?

Cleanest counties in Maine

Share of monitored days rated Good (AQI 0–50)

  1. 1 Knox County 97.8%
  2. 2 York County 96.7%
  3. 3 Sagadahoc County 95.4%
  4. 4 Washington County 91.5%
  5. 5 Hancock County 91%
  6. 6 Androscoggin County 85.2%
  7. 7 Kennebec County 85.2%
  8. 8 Penobscot County 84.2%
  9. 9 Aroostook County 83.3%
  10. 10 Oxford County 75.9%
  11. 11 Cumberland County 74.3%

Good-day share · EPA Air Quality System

County Good % Median AQI
Knox 97.8% 33
York 96.7% 34
Sagadahoc 95.4% 35
Washington 91.5% 34
Hancock 91.0% 35
Androscoggin 85.2% 34
Kennebec 85.2% 34
Penobscot 84.2% 33
Aroostook 83.3% 32
Oxford 75.9% 38
Cumberland 74.3% 39

Data Sources

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

Coverage: 11 counties in Maine with active monitoring stations. Unmonitored counties are not represented.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025

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.

Informational only, not professional advice. Data from EPA AQS. See our disclaimer.