TOAR Health (IMAGE) University of Colorado at Boulder Caption Average number of days per year (2010-2014 average) when ozone levels exceed the US health-based air quality standard of 70 parts per billion (ppb) averaged over eight hours, at non-urban and urban sites. People in parts of California, Arizona, Colorado, Texas, the Midwest and the Middle Atlantic experienced more than 15 days a year with ozone pollution readings higher than 70 ppb. Credit TOAR/Elementa Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.