In 1970, the U.S. Environmental Protection Agency (EPA) established federal limits on the ground-level ozone (smog) concentration permitted in outdoor air with the creation of the Clean Air Act. These limits were health-based and were designed to ensure that citizens would breathe clean, healthy, safe air.

For several years, Indianapolis' ground-level ozone levels did not meet federal air quality standards, and the city was designated as non-attainment. Thanks to years of hard work from area residents and businesses, Indianapolis reduced ground-level ozone levels below the federal standards and returned to attainment status in November 1994.

With the goal of improving regional air quality, Indianapolis launched Knozone in 1996. For more than ten years, Knozone has worked to educate area residents about air pollution and to encourage voluntary actions that will improve air quality at home, at work and at play.

However, central Indiana as a whole, like many major metropolitan areas across the country, now is in violation of federal air quality standards again. This is not because the regional air quality is worsening; rather, federal ground-level ozone standards have become stricter in recent years.

In 2004, the EPA implemented a new, more restrictive air quality standard for ground-level ozone concentrations. As a reult of that new ozone standard, all nine counties in central Indiana have been designated as non-attainment by the U.S. EPA. central Indiana will fail to meet ozone standards if current air pollution levels continue.

In addition, in April 2005, the U.S. EPA designated Indianapolis-Marion County as well as Hamilton, Hendricks, Johnson and Morgan counties as not attaining the federal standard for fine particles (soot), or PM 2.5. For this reason, Knozone evolved into a year-round air quality awareness program for central Indiana in 2005.