Month: October 2015

2015 National Ambient Air Quality Standards for Ozone

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In accordance with a federal court order, the United States Environmental Protection Agency (USEPA) signed a final rule on October 1, 2015, revising the National Ambient Air Quality Standards (NAAQS) for ground level ozone, lowering the primary and secondary standards to 70 ppb, a decrease of 5 ppb from the 2008 ozone NAAQS. The USEPA believes that this standard should be attainable for most areas based on the implementation of other large regulations recently promulgated, e.g., Tier 3 vehicle standards, the Mercury and Air Toxics Standards (MATS) and the Clean Power Plan. The rule was published in the Federal Register on October 26, 2015, and becomes effective on December 28, 2015.

Based on clinical studies and analyses of the effect of ozone exposure, the USEPA concluded a primary ozone NAAQS of 70 ppb is sufficient to protect public health with an adequate margin of safety. Likewise, the USEPA concluded that a secondary ozone NAAQS of 70 ppb is sufficient to protect public welfare, e.g., protection of the forests in Class I areas. The averaging time and form of the standards will remain the same. Compliance is demonstrated when the fourth-highest daily maximum 8-hour ozone concentration per year, averaged over three years, is less than or equal to 70 ppb. The USEPA deemed the 70 ppb standards to be “requisite to protect public health and welfare,” meaning that the level is neither more nor less stringent than necessary.

The implementation timeline for the 2015 ozone NAAQS is as follows:

  • October 2016 – States recommend non-attainment designations to USEPA, based on monitoring data from the previous three-year period (2013-2015).
  • October 2017 – USEPA makes final non-attainment designations based on monitoring data from 2014-2016.
  • 2020-2021 – State Implementation Plans (SIPs) due (date dependent on severity of non-attainment designation).
  • 2020-2037 – States must comply with the standard (date dependent on severity of non-attainment designation).

As presented above, states are required to submit recommended non-attainment designations to USEPA by October 2016, based on monitoring data from the previous three-year period. USEPA plans to issue guidance documents in early 2016 to facilitate the designation process.

Several states in the western U.S. have expressed concern regarding the impact of background ozone concentration on ambient air quality and counties’ abilities to demonstrate compliance with the more stringent ozone standards. The USEPA believes that background ozone will not prevent areas from attaining the 70 ppb ozone standards; however, to address this concern, USEPA plans to update the Exceptional Events Rule, which allows states to exclude “uncontrollable pollution,” such as increased ozone levels due to wildfires. Additionally, the USEPA plans to issue a white paper on background ozone and hold a stakeholder workshop. The USEPA will also work with states to address interstate transport of ozone and ozone precursors, especially in areas affected by high background concentrations of ozone due to long-range transport of ozone from other countries and wildfires.

The final regulation also provides a transition mechanism for PSD permitting projects currently underway via a grandfathering provision. Projects subject to this provision must demonstrate compliance with the 75 ppb ozone NAAQS standards from 2008 but will not be required to demonstrate compliance with the 2015 standards. This will allow these projects to proceed without the significant delay associated with preparation of a new compliance demonstration. In order to qualify for the provision, the facility must have achieved one of the following milestones:

  • The permitting agency formally determined the application to be complete as of October 1, 2015; or
  • The public notice for a draft permit or preliminary determination will have been published prior to December 28, 2015, the date the revised ozone standards become effective.

For 33 states and regions, the USEPA has also increased the length of the ozone monitoring season to address findings that ozone levels can be elevated earlier in the spring and later in the fall than the current monitoring time frame. This extension ranges from the addition of one month for 22 states and the District of Columbia to an additional seven months for Utah. The revised standard also requires that ozone monitors located at multi-pollutant NCore monitoring sites operate year-round. These changes will become effective January 1, 2017.

Additional changes to the NAAQS include updating the Air Quality Index (AQI), streamlining and modernizing the Photochemical Assessment Monitoring Stations (PAMS) network, and updating the Federal Reference Method for ozone to include an additional method for measuring ozone in outdoor air.

Many state agencies will host stakeholder meetings over the next year as they begin to identify potential ozone non-attainment areas. Check your state’s website to follow their activities.

If you have any questions about the 2015 ozone NAAQS and their implications to your facility, please contact either Amy Ritts (; 888-598-6808). More information on the ozone standards is available at