Median AQI
44
Good
Maryland · County air quality · 2025
Baltimore County, Maryland
Median AQI 44 (Good). 70.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 70.4%
- Good-air days
- 0
- Unhealthy days
- 32%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Baltimore County's air is good on balance, more polluted than the median US county, a median AQI of 44 with 70.4% of 304 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 70.4%
- days rated Good
- Ozone
- main pollutant
- 32%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 129.
Data updated July 2026
- Good · 214 d · 70.4%
- Moderate · 87 d · 28.6%
- USG · 3 d · 1.0%
How did Baltimore County's air break down in 2025?
Across 304 monitored days, 214 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 129 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 304 days monitored. Median AQI: 44 (Good).
Insights: Baltimore County, Maryland. EPA monitors recorded a median Air Quality Index of 44 across 304 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 214 (70%) fell in the Good band (AQI 0–50), 87 (29%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 65, while the worst single-day peak hit 129 (USG). Residents averaged about 21.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (212 days), PM2.5 (92 days). Across the 2020–2025 trend window, good days shifted by -43 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 129, usg but never Unhealthy. Nearby counties show comparable readings: Anne Arundel (87.2% good, AQI 40); 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); Charles (92.4% good, AQI 38).
Air Quality Summary
Good Days
70.4%
214 of 304 monitored days
-4.6pp vs 75% target
Max AQI Recorded
129
USG
Health Grade
Moderate
90th-pct AQI 65
Baltimore County, Good days share 70.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Baltimore 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 304 monitored days across EPA AQI categories.
Good
214
70%
Moderate
87
29%
USG
3
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Baltimore County.
- Ozone · 212 days · 69.7%
- PM2.5 · 92 days · 30.3%
Health Impact Assessment
Moderate
Baltimore County's air quality is rated Moderate based on 70.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 70.4% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 212 of 304 monitored days.
5-Year Air Quality Trend
Air quality is stable in Baltimore County. Best year: 2020 (257 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 257 | 106 | 2 | 0 | 43 | 105 |
| 2021 | 207 | 148 | 10 | 0 | 47 | 140 |
| 2022 | 238 | 126 | 1 | 0 | 45 | 122 |
| 2023 | 228 | 124 | 9 | 3 | 45 | 205 |
| 2024 | 240 | 121 | 5 | 0 | 45 | 115 |
| 2025 | 214 | 87 | 3 | 0 | 44 | 129 |
How does Baltimore County compare?
How Baltimore County compares
Good-day share worse than US avg
Baltimore County 70.4%
Anne Arundel County, Maryland 87.2%
US average 76.5%
Median AQI worse than US avg
Baltimore County 44
Anne Arundel County, Maryland 40
US average 38
Unhealthy days / yr about average
Baltimore 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 Baltimore County.
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
Butte County, Idaho
AQI 44 · 87.4% good
What Baltimore 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 44 means for exposure. Health guidance
- See how Baltimore County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Baltimore County with its Maryland neighbours before drawing a conclusion about the region. All of Maryland
Based on 304 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 Baltimore County, Maryland? ▼
Baltimore County has a median Air Quality Index (AQI) of 44, rated "Good." 70.4% of monitored days (214 out of 304) had good air quality in 2025.
What is the main pollutant in Baltimore County? ▼
The primary pollutant in Baltimore County is Ozone (O3), which was the main AQI driver on 212 days (70% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Baltimore County have? ▼
In 2025, Baltimore County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 129.
Is the air quality in Baltimore County getting better or worse? ▼
Air quality in Baltimore County is stable based on 5-year trends (2020-2025). Best year: 2020 with 257 good days. Worst year: 2021 with 207 good days.
What does AQI 44 mean for health? ▼
Baltimore County's median AQI of 44 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 Baltimore County compare to other counties in Maryland? ▼
Baltimore County has 70.4% good air days. Nearby counties in Maryland: Anne Arundel (87.2% good), Baltimore (City) (68.7% good), Calvert (94.6% good), Carroll (90.3% good), Cecil (80.9% good), Charles (92.4% good).
What is the 90th percentile AQI in Baltimore County? ▼
The 90th percentile AQI for Baltimore County is 65, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 129 (USG).
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.