# Counties in Maryland by highest daily 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_max`
- Unit: index
- Definition: Highest daily Air Quality Index (AQI) value recorded in a US county during the year, from the EPA AirData annual summaries. Values above 500 are beyond the AQI scale and are published as EPA computes them.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: highest 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: highest daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/highest-daily-air-quality-index/maryland-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Harford County | 143 |
| 2 | Baltimore city | 136 |
| 3 | Baltimore County | 129 |
| 3 | Cecil County | 129 |
| 3 | Kent County | 129 |
| 6 | Prince George's County | 126 |
| 7 | Anne Arundel County | 119 |
| 8 | Charles County | 97 |
| 9 | Frederick County | 93 |
| 10 | Carroll County | 90 |
| 10 | Montgomery County | 90 |
| 10 | Washington County | 90 |
| 13 | Dorchester County | 84 |
| 14 | Garrett County | 80 |
| 15 | Howard County | 78 |
| 16 | Calvert County | 77 |