Thousands of residents in South Dakota—including the Badlands National Park, Haakon County, and Bennett County—have been advised to stay inside by the U.S. Environmental Protection Agency (EPA) as levels of fine particle pollution (PM2.5) reached “very unhealthy” levels on Sunday, December 28, 2025, at 4 a.m., according to an AirNow map.
The EPA uses AirNow as a platform to monitor and communicate air quality information across the United States. AirNow uses the Air Quality Index (AQI), which is a standardized system developed by the EPA that categorizes the air quality into six color-coded levels with scores ranging from 0 to 301+ to establish how good the air quality is, per region, based on the amount of pollution—including ozone and particulate matter (PM2.5 and PM10)—in the atmosphere.
The six AQI categories are:
- Good (green): Good has a score of between 0-50, meaning the air quality is considered satisfactory, and air pollution poses little or no risk.
- Moderate (yellow): Moderate has a score of between 51-100, which means the air quality is acceptable; however, there may be a risk for some people who are unusually sensitive to air pollution.
- Unhealthy for Sensitive Groups (orange): Unhealthy for sensitive groups has a score of between 101–150 and means that members of sensitive groups—including children, the elderly, and people with heart or lung conditions—may experience health effects. The general public is less likely to be affected.
- Unhealthy (red): Unhealthy has a score of between 151-200, and means everyone may begin to experience health effects; sensitive groups may experience more serious effects.
- Very Unhealthy (purple): Very unhealthy has a score of between 201-300 and means that the risk of health effects is increased for everyone.
- Hazardous (maroon): Hazardous is the highest AQI level, and has a score of 301 or higher, meaning the EPA is issuing health warnings of emergency conditions. The entire population is likely to be affected.
In this case, AirNow recorded a “very unhealthy” AQI score for certain parts of South Dakota due to elevated levels of PM2.5.
PM2.5 are tiny, inhalable particles of pollution—smaller than a strand of hair—that can enter the bloodstream and lungs, triggering or exacerbating health conditions or causing uncomfortable symptoms like coughing, nose, throat, and ear irritation, and shortness of breath.
The EPA is therefore urging vulnerable people in affected areas to avoid all physical outdoor activity, and everyone else to try to avoid long or intense outdoor activities.
The EPA has issued outdoor activity guidelines which say, when the air quality is “very unhealthy”: “Sensitive groups: Avoid all physical activity outdoors. Reschedule to a time when air quality is better or move activities indoors. Everyone else: Avoid long or intense activities. Consider rescheduling or moving activities indoors.”
It also said: “Particle pollution causes a number of serious health problems, including coughing, wheezing, reduced lung function, asthma attacks, heart attacks and strokes. It also is linked to early death in people with heart or lung disease. Fine particles (2.5 micrometers in diameter and smaller) come from power plants, industrial processes, vehicle tailpipes, woodstoves, and wildfires.”
People in affected areas should continue to monitor the AirNow map for updates, as conditions could change rapidly.
