Today, EPA Administrator Gina McCarthy announced the signing of a final rule that reduces the National Ambient Air Quality Standard (NAAQS) for ozone from 75 parts per billion (ppb) to 70 ppb.
The CAA requires the NAAQS to be reviewed every 5 years. EPA must review relevant scientific data and set the NAAQS at a level that “in the judgement of the Administrator” is “requisite to protect the public health” with “an adequate margin of safety.”
In November 2014, the EPA proposed to revise the existing ozone NAAQS to a level within the range of 65 to 70 ppb. Administrator McCarthy settled on 70 ppb, citing the following:
- It eliminates exposure at 72 ppb, which is the lowest exposure known to cause harmful health effects in healthy adults, and
- For 98 percent of children, it eliminates repeated exposure to ozone concentrations as low as 60 ppb.
Based on 2014, 2015, and 2016 data and regulations already in place, EPA expects numerous counties in California, but just 14 counties outside of California, to be in nonattainment in 2025. Nonattainment designations are expected in 2017, with attainment dates stretching from 2020 to 2037.