Median AQI
38
Good
Maryland · County air quality · 2025
Charles County, Maryland
Median AQI 38 (Good). 92.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 92.4%
- Good-air days
- 0
- Unhealthy days
- 81%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Charles County's air is good on balance, cleaner than most US counties, a median AQI of 38 with 92.4% of 236 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 92.4%
- days rated Good
- Ozone
- main pollutant
- 81%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 97.
Data updated July 2026
- Good · 218 d · 92.4%
- Moderate · 18 d · 7.6%
How did Charles County's air break down in 2025?
Across 236 monitored days, 218 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 97 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 236 days monitored. Median AQI: 38 (Good).
Insights: Charles County, Maryland. EPA monitors recorded a median Air Quality Index of 38 across 236 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 218 (92%) fell in the Good band (AQI 0–50), 18 (8%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 97 (Moderate). Residents averaged about 27.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (236 days). Across the 2020–2025 trend window, good days shifted by -17 and the median AQI moved +4 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 97, moderate but never Unhealthy. Nearby counties show comparable readings: Anne Arundel (87.2% good, AQI 40); Baltimore (70.4% good, AQI 44); Baltimore (City) (68.7% good, AQI 44); Calvert (94.6% good, AQI 38); Carroll (90.3% good, AQI 38); Cecil (80.9% good, AQI 41).
Air Quality Summary
Good Days
92.4%
218 of 236 monitored days
17.4pp vs 75% target
Max AQI Recorded
97
Moderate
Health Grade
Excellent
90th-pct AQI 49
Charles County, Good days share 92.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Charles County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 236 monitored days across EPA AQI categories.
Good
218
92%
Moderate
18
8%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Charles County.
- Ozone · 236 days · 100.0%
Health Impact Assessment
Excellent
Charles County's air quality is rated Excellent based on 92.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 92.4% of monitored days in 2025, with a median AQI of 38. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 236 of 236 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Charles County. Best year: 2020 (235 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 235 | 1 | 0 | 0 | 34 | 58 |
| 2021 | 215 | 26 | 1 | 0 | 38 | 105 |
| 2022 | 225 | 20 | 0 | 0 | 41 | 87 |
| 2023 | 199 | 42 | 2 | 0 | 42 | 115 |
| 2024 | 209 | 21 | 2 | 0 | 40 | 119 |
| 2025 | 218 | 18 | 0 | 0 | 38 | 97 |
How does Charles County compare?
How Charles County compares
Good-day share better than US avg
Charles County 92.4%
Anne Arundel County, Maryland 87.2%
US average 76.5%
Median AQI about average
Charles County 38
Anne Arundel County, Maryland 40
US average 38
Unhealthy days / yr about average
Charles County 0
Anne Arundel County, Maryland 0
US average 0
Other Counties in Maryland
Air quality comparison for nearby counties in Maryland.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Charles County.
Adams County, Illinois
AQI 38 · 94.4% good
Anoka County, Minnesota
AQI 38 · 82.1% good
Atlantic County, New Jersey
AQI 38 · 79.6% good
Avery County, North Carolina
AQI 38 · 93.9% good
Barnstable County, Massachusetts
AQI 38 · 92.5% good
Bay County, Michigan
AQI 38 · 71.8% good
What Charles County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 38 means for exposure. Health guidance
- See how Charles County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Charles County with its Maryland neighbours before drawing a conclusion about the region. All of Maryland
Based on 236 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Charles County, Maryland? ▼
Charles County has a median Air Quality Index (AQI) of 38, rated "Good." 92.4% of monitored days (218 out of 236) had good air quality in 2025.
What is the main pollutant in Charles County? ▼
The primary pollutant in Charles County is Ozone (O3), which was the main AQI driver on 236 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Charles County have? ▼
In 2025, Charles County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 97.
Is the air quality in Charles County getting better or worse? ▼
Air quality in Charles County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 235 good days. Worst year: 2023 with 199 good days.
What does AQI 38 mean for health? ▼
Charles County's median AQI of 38 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Charles County compare to other counties in Maryland? ▼
Charles County has 92.4% good air days. Nearby counties in Maryland: Anne Arundel (87.2% good), Baltimore (70.4% good), Baltimore (City) (68.7% good), Calvert (94.6% good), Carroll (90.3% good), Cecil (80.9% good).
What is the 90th percentile AQI in Charles County? ▼
The 90th percentile AQI for Charles County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 97 (Moderate).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
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.