The 1-Hour Ozone Standard
The 1-hour primary and secondary federal standards for ozone were each set at a level of 0.12 ppm. The standards were attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm was equal to or less than 1, averaged over 3 years (i.e., no more than 3 exceedances in 3 years). Current emissions control strategies focus on reducing the highest hourly average concentrations.