State Health authorities on Saturday advised people with heart or lung conditions, children and the elderly to limit their activities because of high pollution levels in a north-central Colorado county.
Pollution levels were expected to be unhealthy for sensitive groups through at least Sunday morning, the Colorado Department of Public Health and Environment said. Prolonged or heavy exertion either inside or outside is not recommended.
The advisory covers central and southern Weld County including the city of Greeley.
Cold, stagnant weather has allowed the concentrations of small particles of pollution in the air to climb in the area, the agency said.