Median AQI
38
Good
Maryland · County air quality · 2025
Carroll County, Maryland
Median AQI 38 (Good). 90.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 90.3%
- Good-air days
- 0
- Unhealthy days
- 76%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Carroll County's air is good on balance, cleaner than most US counties, a median AQI of 38 with 90.3% of 238 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 90.3%
- days rated Good
- Ozone
- main pollutant
- 76%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 90.
Data updated July 2026
- Good · 215 d · 90.3%
- Moderate · 23 d · 9.7%
How did Carroll County's air break down in 2025?
Across 238 monitored days, 215 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 90 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 238 days monitored. Median AQI: 38 (Good).
Insights: Carroll County, Maryland. EPA monitors recorded a median Air Quality Index of 38 across 238 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 215 (90%) fell in the Good band (AQI 0–50), 23 (10%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 50, while the worst single-day peak hit 90 (Moderate). Residents averaged about 27.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (238 days). Across the 2020–2025 trend window, good days shifted by -10 and the median AQI moved -1 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 90, 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); Cecil (80.9% good, AQI 41); Charles (92.4% good, AQI 38).
Air Quality Summary
Good Days
90.3%
215 of 238 monitored days
15.3pp vs 75% target
Max AQI Recorded
90
Moderate
Health Grade
Excellent
90th-pct AQI 50
Carroll County, Good days share 90.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Carroll 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 238 monitored days across EPA AQI categories.
Good
215
90%
Moderate
23
10%
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 Carroll County.
- Ozone · 238 days · 100.0%
Health Impact Assessment
Excellent
Carroll County's air quality is rated Excellent based on 90.3% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 90.3% 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 238 of 238 monitored days.
5-Year Air Quality Trend
Air quality is stable in Carroll County. Best year: 2020 (225 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 225 | 17 | 0 | 0 | 39 | 84 |
| 2021 | 208 | 34 | 1 | 0 | 41 | 112 |
| 2022 | 210 | 32 | 1 | 0 | 42 | 112 |
| 2023 | 183 | 57 | 4 | 0 | 44 | 143 |
| 2024 | 189 | 55 | 0 | 0 | 42 | 93 |
| 2025 | 215 | 23 | 0 | 0 | 38 | 90 |
How does Carroll County compare?
How Carroll County compares
Good-day share better than US avg
Carroll County 90.3%
Anne Arundel County, Maryland 87.2%
US average 76.5%
Median AQI about average
Carroll County 38
Anne Arundel County, Maryland 40
US average 38
Unhealthy days / yr about average
Carroll 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 Carroll 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 Carroll 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 Carroll County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Carroll County with its Maryland neighbours before drawing a conclusion about the region. All of Maryland
Based on 238 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 Carroll County, Maryland? ▼
Carroll County has a median Air Quality Index (AQI) of 38, rated "Good." 90.3% of monitored days (215 out of 238) had good air quality in 2025.
What is the main pollutant in Carroll County? ▼
The primary pollutant in Carroll County is Ozone (O3), which was the main AQI driver on 238 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Carroll County have? ▼
In 2025, Carroll County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 90.
Is the air quality in Carroll County getting better or worse? ▼
Air quality in Carroll County is stable based on 5-year trends (2020-2025). Best year: 2020 with 225 good days. Worst year: 2023 with 183 good days.
What does AQI 38 mean for health? ▼
Carroll 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 Carroll County compare to other counties in Maryland? ▼
Carroll County has 90.3% 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), Cecil (80.9% good), Charles (92.4% good).
What is the 90th percentile AQI in Carroll County? ▼
The 90th percentile AQI for Carroll County is 50, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 90 (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.