On October 1, 2015, EPA lowered the National Ambient Air Quality Standards (NAAQS) for ground-level ozone to 70 parts per billion (ppb).  The new standard will replace the 2008 standard of 75 ppb, which EPA found inadequate to protect public health with an adequate margin of safety, as required under the Clean Air Act, and likely will result in changes in ozone attainment designations in a number of areas.

Under the Clean Air Act, EPA is required to set a primary ozone standard to protect public health and a secondary standard to protect public welfare every five years.  Both standards are now set at 70 ppb.

To implement the new standards, EPA anticipates beginning the process of designating attainment and nonattainment areas in early 2016.  The statutory deadline to finalize attainment designations is October 1, 2017.  Areas would then have between 2020 and 2037 to come into compliance with the new standards.  Attainment dates will vary based on the ozone level in the area.

As illustrated by the below map, the lowered standard is expected to have a significant impact on the attainment status of many areas, including many major cities.



[Source: http://www.nam.org/Issues/Energy-and-Environment/Ozone-Regulations/Non-Attainment-Maps-for-Proposed-Ozone-Standard-(Based-on-2008-2010-data)/]

Though permit authorities are generally required to consider the revised ozone standards when issuing preconstruction permits to new or modified major emissions sources, the rule includes a grandfathering provision that requires permitting authorities to consider the prior ozone standard for some sources with pending Prevention of Significant Deterioration and Nonattainment New Source Review permits.

Over the next year, EPA plans to propose additional rules and guidance to help states with nonattainment areas implement the stricter standards, including revisions to its 2007 Exceptional Events Rule to address pollution events outside an area’s control, such as wildfires.