What does this indicator measure?

This indicator measures the air quality every day of the year in Onondaga County, from 2000 to 2011. The number of days with good Air Quality Index (AQI) is a useful measure because it demonstrates the number of days which the EPA has determined as an unhealthy level. AQI is measured on a 0-500 scale with 0-50 representing ‘good’ air quality according to AIRNow. The index measures levels of major air pollutants outlined in the Clean Air Act such as: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Any air quality other than good poses a health threat and short term exposure to poor air quality and prolonged exposure to citizens pose an identified risk.