The level of air pollution varies throughout the United States from a good rating to an unhealthy rating on the air quality index scale, AQI. Prescott, Arizona, Cheyenne, Wyoming and Flagstaff, Arizona have some of the highest air quality ratings as ranked by StateoftheAir.org.
Most states have a rating between zero to 50 on the AQI scale, which is considered good air quality. Some areas fall into the moderate category, between 51 to 100. Areas such as Salt Lake City, Utah and Denver, Colorado have an AQI that falls between 101 to 150, which is considered unhealthy for sensitive groups. Salmon, Idaho has an unhealthy air quality ranking. No place in the country has an AQI within the two worst air quality rankings, which are "unhealthy" and "hazardous."