An Obama-era rule to reduce ground-level ozone has been delayed by one year, EPA Administrator Scott Pruitt announced Tuesday. The National Ambient Air Quality Standards were supposed to identify cities that currently have ozone levels above 70 parts per billion. The EPA itself calls ground-level ozone “bad ozone” and says it has been linked to numerous environmental and health effects, including “chest pain, coughing, throat irritation, and airway inflammation,” which can lead the asthma or other problems. The announcement about this delay, however, claims the EPA does not “fully understand the role of background ozone levels.”