* Data calculated by dividing by the number of days with recorded Air Quality Index Values. PM10 monitoring started in 1988 and PM2.5 monitoring was phased in between 1999 and 2001. When tracking trends that include PM2.5, the EPA includes years 2000 and later.
Years Available: 1980–2019
Permanent Link: http://data.sagepub.com/sagestats/4142
General Notes: *Median value gives the value for the "average" county for this metric, the 50th percentile of all counties reporting data. **Very Unhealthy is defined as an AQI of over 201. This includes the AQI categories very unhealthy and hazardous. Very few locations (about 0.3% of counties) have any days in the very unhealthy or hazardous categories. Value calculated by SAGE using total days reported by county. See source for original data.