State air quality · 2025

Maryland Air Quality Ranking

Across 16 monitored counties, the typical county in Maryland posts a median AQI of 40 (Good) and 81.8% of monitored days were rated Good, from EPA AQS.

40
Avg median AQI
81.8%
Good-air days
16
Counties monitored
73%
Cleaner than US states

Maryland's typical county median AQI is 40 (Good) across 16 monitored counties

According to the U.S. EPA Air Quality System, Maryland monitors 16 counties with a day-weighted Good-day share of 81.8%. Cleanest: Calvert County (94.6% Good). Most polluted: Baltimore County (64.7%). These are annual summaries, not live AirNow readings.

Data source EPA Air Quality System (AQS)

Cleaner than US states
Maryland's day-weighted Good-day share of 81.8% places it cleaner than 73% of US states.
In-state spread
Within Maryland, Calvert County leads at 94.6% Good days while Baltimore County sits at 64.7% across 16 monitored counties.
2024→2025 release
Maryland's Good-day share moved +4.3 points vs the 2024 EPA annual release.
Typical median AQI
Typical median AQI: 40

Verify with AirNow → · EPA AQS →

EPA state monitoring brief

AQS state key MARYLAND

Maryland · 2025 EPA AQS · 16 counties · med AQI 40 · 81.8% Good · Calvert→Baltimore spread

  • GOOD 40 Median AQI · Good
  • SHARE 81.8% Good-day share
  • COUNT 16 Counties monitored
  • UNH 0 Unhealthy+ days
  • RANK 73% Cleaner than states
  • O3 64.7% Main pollutant share

Good-day share peers

Washington82.2%Maryland (this)81.8%New York81.3%North Carolina81%
Good-day share neighbourhood · nearest ABS peers vs Maryland

Maryland's 81.8% Good-day share is cleaner than 73% of monitored US states; Calvert and Baltimore County bracket the in-state range. Open Calvert County →

According to EPA AQS annual summaries on PlainAirData, Maryland ranks #14 of 52 by day-weighted good-day share (81.8%) and #29 by mean county median AQI (39.6). 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

81.8%

Good-day share in 2025, up 4.3 percentage points vs 2024. County-mean median AQI 40, 0.9 points lower (cleaner) than 2024.

Pollutant mix

Ozone

Main driver on 64.7% of pollutant-assigned days.

  • Ozone 64.7%
  • PM2.5 33.1%
  • NO2 1.8%
  • PM10 0.4%

Monitoring coverage

324

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

Counties Monitored

16

Good Days %

81.8%

Avg Median AQI

40

Total Unhealthy Days

0

Best Air Quality

Calvert County

Worst Air Quality

Baltimore County

Where Maryland sits nationally

COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Maryland's day-weighted Good-day share is 81.8% - cleaner than 73% of that comparison set.

Maryland Good-day share vs. every US state

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

81.8% Cleaner than 73% higher than 73% 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%). This entry sits in this band. 85.0%–90.0%: 5 US states (10%). Above this entry. 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 Maryland have the cleanest and most polluted air?

Cleanest counties in Maryland

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

  1. 1 Calvert County 94.6%
  2. 2 Charles County 92.4%
  3. 3 Carroll County 90.3%
  4. 4 Anne Arundel County 87.6%
  5. 5 Garrett County 87.1%
  6. 6 Dorchester County 86%
  7. 7 Frederick County 85.7%
  8. 8 Kent County 84%
  9. 9 Prince George's County 83.8%
  10. 10 Montgomery County 83.1%
  11. 11 Howard County 80.3%
  12. 12 Cecil County 79.8%

Good-day share · EPA Air Quality System

County Good % Median AQI
Calvert 94.6% 38
Charles 92.4% 38
Carroll 90.3% 38
Anne Arundel 87.6% 40
Garrett 87.1% 39
Dorchester 86.0% 39
Frederick 85.7% 41
Kent 84.0% 38
Prince George's 83.8% 40
Montgomery 83.1% 39
Howard 80.3% 33
Cecil 79.8% 41
Washington 79.0% 40
Harford 75.5% 42
Baltimore (City) 68.1% 43
Baltimore 64.7% 45

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: 16 counties in Maryland 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.