Is the Air Quality Good in Cass, North Dakota?
Mostly — air quality in Cass, North Dakota is fair, not pristine. The city earns a Grade of C (fair) on a 5-year median AQI of 41 (Good), with 32 unhealthy-air days over five years (about 6 per year). Healthy adults are fine most of the time, but sensitive groups should watch the daily forecast.
Who Can Safely Breathe the Air in Cass, North Dakota?
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.
Across the past five years, this area has logged 32 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 6 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Cass, North Dakota Air Quality Snapshot
| Air Quality Grade | C59/100 |
| 5-Year Median AQI | 41 (Good) |
| Most Recent Median AQI (2023) | 50 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Worsening (+0.46 AQI/yr) |
| Unhealthy Days (last 5 yr) | 32 |
| National Rank (cleanest = #1) | #548 of 1,020 (54th most polluted percentile) |
| North Dakota Rank | #10 of 10 |
What Does the C Grade Mean?
Cass, North Dakota earns a C — air quality is fair, but not great. With a 5-year median AQI of 41, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Cass, North Dakota's 5-year median AQI of 41 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within North Dakota, Cass, North Dakota runs more polluted than the state average of 37 — local sources or geography are concentrating pollution above the state's typical reading.
For context within North Dakota: Williams, North Dakota currently holds the state's cleanest grade (B, AQI 34), while Ward, North Dakota sits at the bottom (C, AQI 36).
What's in Cass, North Dakota's Air?
The dominant pollutant in Cass, North Dakota is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 245 | 68% |
| Ground-Level Ozone | 112 | 31% |
| Nitrogen Dioxide | 1 | 0% |
Is the Air Getting Better or Worse?
Air quality in Cass, North Dakota has been getting worse over the past decade, with median AQI climbing by roughly 0.5 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.
In 2014, Cass, North Dakota posted a median AQI of 37. By 2023 that figure was 50 — a rise of 13 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Cass, North Dakota
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 37 | 285 | 1 | Ozone |
| 2015 | 46 | 235 | 3 | PM2.5 |
| 2016 | 37 | 263 | 0 | Ozone |
| 2017 | 44 | 232 | 0 | PM2.5 |
| 2018 | 39 | 271 | 1 | Ozone |
| 2019 | 36 | 301 | 2 | Ozone |
| 2020 | 37 | 303 | 0 | Ozone |
| 2021 | 42 | 227 | 17 | PM2.5 |
| 2022 | 40 | 285 | 1 | PM2.5 |
| 2023 | 50 | 180 | 12 | PM2.5 |
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
More about Cass, North Dakota
Cass, North Dakota has an Air Quality Grade of C (fair) with a 5-year median AQI of 41. The dominant pollutant is Ground-Level Ozone, and air quality has been worsening over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.