Air Quality Rankings for North Dakota 2026
North Dakota has 10 cities with EPA air quality data. Williams, North Dakota has the cleanest air with a 5-year average AQI of 34. Cass, North Dakota has the highest AQI at 41.
| # | City | 5yr Avg AQI | Current AQI | Worst Pollutant | Trend | Grade |
|---|---|---|---|---|---|---|
| 1 | Williams, North Dakota | 34 | 34 | Ozone | Stable | B |
| 2 | McKenzie, North Dakota | 36 | 39 | Ozone | Stable | C |
| 3 | Ward, North Dakota | 36 | 42 | Ozone | Worsening | C |
| 4 | Billings, North Dakota | 37 | 39 | Ozone | Stable | C |
| 5 | Dunn, North Dakota | 37 | 41 | Ozone | Worsening | C |
| 6 | Mercer, North Dakota | 38 | 41 | Ozone | Worsening | C |
| 7 | Burke, North Dakota | 38 | 44 | Ozone | Worsening | C |
| 8 | Burleigh, North Dakota | 38 | 42 | PM2.5 | Worsening | C |
| 9 | Oliver, North Dakota | 39 | 42 | Ozone | Worsening | C |
| 10 | Cass, North Dakota | 41 | 50 | Ozone | Worsening | C |
Air quality data for North Dakota is sourced from the EPA Air Quality System (AQS), which monitors outdoor air quality at thousands of stations nationwide.
Frequently Asked Questions
Williams, North Dakota has the best air quality in North Dakota with a 5-year average AQI of 34 and a grade of B.
North Dakota has 10 cities with EPA air quality monitoring data in our database, covering multiple years of AQI measurements.
The Air Quality Index (AQI) measures five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Lower AQI values indicate cleaner air — 0-50 is "Good," while 150+ is "Unhealthy."
Cities ranked by 5-year average AQI (lower is better). Grades factor in average AQI, trend direction, unhealthy days, and dominant pollutant.