Baltimore Air Quality in September
Across 2019–2025, Baltimore's September air quality had a median AQI of 45 (Good) over 210 monitored days in the Baltimore-Columbia-Towson, MD area. 1.0% of September days (2 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 62.4% of days. The cleanest September on record here was 2020 (median AQI 41, 0 days above 100) and the worst was 2019 (median 52, 1 day above 100, peak AQI 122).
- Good: 65.7%
- Moderate: 33.3%
- Unhealthy for Sensitive Groups: 1.0%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Baltimore
Today's main pollutant in Baltimore is ground-level ozone (AQI 23). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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How is the air in Baltimore in September?
Good on a typical day: median AQI 45 across 2019–2025, with 1.0% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓65.7% of September days were Good (AQI 0–50), 33.3% Moderate (51–100).
- ✓2 days of 210 reached AQI 101+; the September peak was 122.
- ✓Best September: 2020; worst September: 2019.
Frequently asked questions
What is the air quality like in Baltimore in September?▾
Across 2019–2025, the median daily AQI in Baltimore in September was 45 (Good). 65.7% of days were Good, 33.3% Moderate, and 1.0% reached Unhealthy for Sensitive Groups or worse, based on 210 monitored days in EPA's Air Quality System.
Is September a good time for outdoor exercise in Baltimore?▾
A typical September day in Baltimore sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of September days (1.0%) reached AQI 101+ in 2019–2025.
Which pollutant causes Baltimore's September air quality problems?▾
Ground-level ozone set the daily AQI on 62.4% of September days in Baltimore. The highest September AQI recorded in 2019–2025 was 122 (Unhealthy for Sensitive Groups), in 2019.
Baltimore September air quality, year by year
Baltimore September air quality by year (Baltimore-Columbia-Towson, MD, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 30 | 52 | 1 | 122 | O3 |
| 2020cleanest | 30 | 41 | 0 | 71 | PM2.5 |
| 2021 | 30 | 46 | 0 | 84 | PM2.5 |
| 2022 | 30 | 43 | 0 | 74 | O3 |
| 2023 | 30 | 44 | 1 | 105 | O3 |
| 2024 | 30 | 43 | 0 | 90 | O3 |
| 2025 | 30 | 49 | 0 | 87 | O3 |
What September air means in Baltimore
A typical September day in Baltimore sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of September days (1.0%) reached AQI 101+ in 2019–2025.
September's median AQI of 45 is below Baltimore's whole-year median of 49, making it one of the area's cleaner periods. Nationally, the median September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so Baltimore runs in line with the national September norm; 1.0% of its September days topped AQI 100 versus 2.7% nationally (below average).
September is part of Baltimore's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Baltimore
The latest EPA AirNow observation puts Baltimore's AQI at 23 (O3). The figures above are multi-year month statistics, not today's reading.
View current Baltimore air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Baltimore-Columbia-Towson, MD), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.