Indicators 2014: Air Quality

Air Quality Index
The Air Quality Index (AQI) is a measurement used to communicate  the level of air pollution to the public. With increasing levels of pollution, the index number will increase. These numbers are determined by calculating the average of readings over a period of time. For Forsyth County, the air quality is calculated hourly at multiple monitoring stations. Each pollutant is measured and considered in the final index.
The AQI is calculated using standards set by the Clean Air Act (CAA). The standards relating to the CCA are focused in on six common pollutants: particulate matter (PM), ozone (O3), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and lead (Pb).
Levels of Air Quality Index
The chart describes the AQI levels and associated index range. If an area reports an AQI of 25, then that day falls within the ‘Good’ range. However, if they report an AQI of 115, this falls within the orange category: ‘Unhealthy for Sensitive Groups' and so forth. Each level has suggested level of outdoor activity for certain groups of people.
Within the last ten years, the level of pollutants for selected counties in North Carolina has seen some rises and falls. Reasons for these fluctuations may be changes in tighter or more flexible regulations. For example, on October 1, 2015, the EPA announced new standards for ground-level ozone. (1)

Figure 1: Air Quality, Forsyth County Trend, 2004-2014
  • Forsyth County has increased the number of ‘good’ air quality days.

Figure 2: Air Quality, Percent of Days with AQI over 100, Forsyth County Trend, 2004-2014
  • This figure shows a spike in the percent of days with AQIs over 100 in 2007 followed by a sharp decrease continuing for two more consecutive years.
  • From 2004 to 2014, there has been an overall drop from 5% to 0% of days reported with an AQI over 100.

Figure 3: Air Quality, Percent of Days with AQI over 100, Major Urban County Trend Comparison, 2004-2014
  • The trend for NC's major urban counties all followed the same general pattern.

Explore More
To explore the dataset that this report is based on click here.
To explore more Environmental Sustainability data available through Forsyth Futures click here.

Last Update: December 2015
(1). United States Environmental Protection Agency. (2015, December 23). Regulatory Information by Topic: Air. Retrieved from
For more information, please contact Megan Grigg at