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In October 2015, the U.S. EPA signed a notice of final rulemaking that lowered the 8-hour primary and secondary ozone National Ambient Air Quality Standards (NAAQS) from 0.075 parts per million (ppm) to 0.070 ppm. When a NAAQS is established or revised, EPA and the states must act to ensure that the NAAQS are met. The first step in this process is to identify locations that meet and do not meet the NAAQS, known as the "initial area designations."

The Clean Air Act (CAA) states that initial area designations shall be completed no later than two years from the date of promulgation of a new or revised NAAQS, although it may be extended for up to one year in the event that there is insufficient information to promulgate the designations. EPA Administrator Scott Pruitt announced in June 2017 that he would extend the deadline for promulgating initial area designations by one year to October 1, 2018. This action is not uncommon as past EPA Administrators have extended deadlines to complete designations for other NAAQS.

Since June, EPA has concluded that there is more information available than previously thought. Thus, on August 2, Administrator Pruitt signed a notice withdrawing the one-year extension of the deadline for promulgating initial area designations. The original deadline of October 1, 2017 now applies. The prepublication version of this notice can be found here (for use as a reference rather than for purposes of compliance). The official version of the notice will be published in a forthcoming Federal Register publication and on