# Counties in North Dakota by highest daily Air Quality Index (US EPA), 2001

All 12 values come from U.S. Environmental Protection Agency for 2001, 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/north-dakota-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Cass County | 104 |
| 2 | Grand Forks County | 99 |
| 3 | McKenzie County | 84 |
| 3 | Oliver County | 84 |
| 5 | Mercer County | 83 |
| 6 | Burke County | 77 |
| 7 | Burleigh County | 75 |
| 8 | Dunn County | 74 |
| 9 | Steele County | 68 |
| 10 | Billings County | 67 |
| 11 | Stark County | 65 |
| 12 | McLean County | 34 |