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The United States Environmental Protection Agency (EPA) is implementing the national ambient air quality standards (NAAQS) for ozone that were issued in 2015.

Ground-level ozone is a gas that is formed by the reaction of volatile organic compounds and oxides of nitrogen in the atmosphere in the presence of sunlight. On October 1, 2015, the U.S EPA adopted a new more stringent 8-hour ozone standard that is set at 0.070 parts per million (or 70 part per billion). The final rule for the 2015 8-hour ozone National Ambient Air Quality Standard (NAAQS) was published October 26, 2015.

On November 16, 2017 EPA established initial air quality designations for the 2015 ozone NAAQS. About 85% of the country was designated "attainment/unclassifiable" and the remaining counties were not yet designated. The designations are based on the most recent three years of certified ozone air quality monitoring data and five-factor analysis to assess the ozone contributions of nearby areas. These preliminary designations were reviewed by states and tribes, who had the opportunity to comment on their agreement with or disagreement with the EPA's designations.

On December 22, 2017, EPA responded to state and tribal recommendations by indicating the anticipated area designations for the portions of the country not already designated for the 2015 ozone standards. These responses started a 120-day period in accordance with Section 107(d) of the Clean Air Act (CAA) for states and tribes to provide additional information before EPA determines the final designations.

There were a variety of comments received and addressed by the EPA during the 120-day comment period. The most common comment, that wasn't state or region specific, was in regards to super-regional areas. Many commenters (especially those in the northeastern United States) wanted to have the nonattainment areas expanded to include areas that are near big cities that may have increased ozone due to long range transport (and other mechanisms). The EPA disagreed because the NAAQS specifically only addresses "nearby" areas in their five-factor analysis. In addition, long range transport of ozone is already addressed by other regulations, such as the ozone transport region (OTR) and cross-state air pollution rule (CASPR).

The 120-day period ended on April 30, 2018 and designations for all areas (excepting eight counties in San Antonio, Texas - final designation for these counties will be issued by July 17, 2018) were published in table form and figure form. EPA Administrator E. Scott Pruitt signed the following notice which will be published in the Federal Register soon. The final designations will take effect 60 days after the notice is published in the Federal Register. More information can be found in EPA's public docket, EPA-HQ-OAR-2017-0548.

In the final designation, 51 areas are designated as nonattainment areas. Seven of the nonattainment areas cover multiple states.

Here is a list of counties where the state did not provide nonattainment recommendations, and the EPA had on a list of intended nonattainment. In the final rule some of these counties were designated as nonattainment and some, after further review, were designated attainment/unclassified.

Lake County IN
Clark County IN
Floyd Count IN
Bullitt County KY
Jefferson County KY
Oldham County KY
Franklin County MO
City of St Louis MO
St Charles MO
Kenosha WI (partial)
Door WI (partial)
Manitowoc WI (partial)
Sheboygan WI (partial)
Milwaukee WI
Ozaukee WI

Porter County IN
Dearborn County OH
Jefferson County MO
Cumberland County PA
Douphin County PA
Lancaster County PA
York County PA
Berks County PA
Racine WI
Washington WI
Waukesha WI





The EPA lacks authority to make NAAQS determinations on Indian County land. However, at the request of the Pechanga Tribe and the Morongo Tribe (Southern California) the EPA has provided nonattainment designations for the Indian Counties (as well as the surrounding areas). It is the hope that by providing proposed classification of these areas the planning by the state and tribes will complement each other as the area progresses away from nonattainment.

The EPA proposed that six areas in California retain their voluntary requested higher classification level of ozone nonattainment (these areas also retain a higher classification for the 1997 ozone NAAQS and the 2008 ozone NAAQS). After further review, the state of California declined reclassification for five out of the six areas, with Sacramento Metro area declining voluntary reclassification.

After final notice in the Federal Register is published, states have 30 days to ask for areas to be reclassified. For an area to be eligible to be reclassified, the area's design value must be within 5 percent of the upper or lower limit for the next lower or upper classification.

Some of the state's comments included concerns about the timeline - this NAAQS was first published in 2015, but will not be final until Q3 of 2018. A May 9, 2018 memorandum by E. Scott Pruitt seeks to change the timelines for how the NAAQS reviews and implementations occur in the future. Pruitt sets out five principles to be implemented in the current review of the 2015 ozone NAAQS and the upcoming review of the particulate matter NAAQS. These principles are:

  1. Meet statutory deadlines;
  2. Address all Clean Air Act (CAA) provisions for NAAQS reviews;
  3. Streamline and standardize the process for development and review of key policy-relevant information;
  4. Differentiate science and policy judgements in the NAAQS review process; and
  5. Issue timely implementation regulations and guidance.

The CAA requires each NAAQS to be reviewed every five years, but in reality, each NAAQS is reviewed approximately every ten years. Pruitt would like the EPA to seek efficiencies to shorten the review period. The EPA will be developing a standardized set of key CAA questions for the Clean Air Scientific Advisory Committee (CASAC) to frame and focus the NAAQS review. More robust drafts, appropriate for distribution to other branches of the agency and the general public for comments will be prepared to avoid recirculation of multiple drafts. In addition, a more efficient scientific assessment and policy review with a clear delineation between science and policy will be presented to the Administrator so they can make an informed decision. Finally, the EPA will strive to release both the regulation and the guidance at the same time so that states may know how to attain and maintain the NAAQS.