# Counties in Maryland by median Air Quality Index (US EPA), 2025

All 16 values come from U.S. Environmental Protection Agency for 2025, so the places are comparable. 3 counties have no value for that period and are not ranked.

- Indicator id: `aqi_median`
- Unit: index
- Definition: Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries. The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide). Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/median-air-quality-index/maryland-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Baltimore County | 45 |
| 2 | Baltimore city | 43 |
| 3 | Harford County | 42 |
| 4 | Cecil County | 41 |
| 4 | Frederick County | 41 |
| 6 | Anne Arundel County | 40 |
| 6 | Prince George's County | 40 |
| 6 | Washington County | 40 |
| 9 | Dorchester County | 39 |
| 9 | Garrett County | 39 |
| 9 | Montgomery County | 39 |
| 12 | Calvert County | 38 |
| 12 | Carroll County | 38 |
| 12 | Charles County | 38 |
| 12 | Kent County | 38 |
| 16 | Howard County | 33 |