Air Quality Index

The DNR uses the Air Quality Index (AQI) [exit DNR] that was developed to make it easier for the public to understand the health signficance of air pollution levels for monitored levels of ozone, particle pollution (also known as particulate matter), and other common air pollutants.

There are over 1,000 monitoring sites around the country, including Wisconsin's network, that measure ozone, particulates and several other air pollutants. Concentrations of these pollutants are then translated into the AQI Index, which ranges from 0 to 500. The higher the AQI value for a pollutant, the greater the health concern. An AQI value of 100 usually corresponds to the national ambient air quality standard (NAAQS) for the pollutant, meaning that pollutant concentrations have reached unhealthy levels. These standards are established by EPA under the Clean Air Act to protect public health and the environment.

Each AQI category has a specific color assigned to make it easier to quickly determine the air quality in communities. You may see the AQI for ozone and PM2.5 reported in your newspaper, local television news, radio station, on the AIRNOW website [Exit DNR] and on the DNR's Air Quality Hotline. To learn more about the AQI color system, you can view an AQI video at the Department of Commerce website [Exit DNR]. The chart below explains the AQI color system used in Wisconsin.

At times, the AQI on DNR's Air Monitoring Network may be different than the federal AirNow website [exit DNR]. This is because AirNow estimates the AQI while DNR uses the official EPA formula for determining the AQI level. You may also notice that the AQI values on DNR's air monitoring [insert link] reports may not match those obtained from EPA's Air Quality System (AQS). These differences are most often an artifact of changes in the NAAQS. When EPA changed the standard for PM2.5, they didn't change the AQI calculations but DNR did in order to update concentration ranges to be more protective of public health and reflect the updated NAAQS.

How do the AQI ranges correspond to ozone and fine particle (PM2.5) concentrations?

The ozone AQI is calculated from 8-hour rolling average concentrations. The PM2.5 AQI is calculated using the 24-hour rolling average concentrations from the continuous monitors. The table below identifies the concentration range for each AQI level.

For real-time monitoring of air quality, visit the Department of Natural Resources' Air Monitoring Network or call the DNR's Air Quality Hotline at 1-866-DAILY AIR (1-866-324-5924).

For more information

• Air Quality Watches and Advisories
• American Lung Association [exit DNR] (phone 1-800-LUNG-USA, or 1-800-586-4872)
• Federal AIRNOW website [exit DNR] - information on ozone and particle pollution mapping, the AQI, and more.
• Map of Wisconsin Counties with Continuous Pollutant Monitors for Ozone and PM2.5