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U.S. EPA Proposed 2015 Ozone NAAQS Implementation Rule

Posted: December 5th, 2016

Author: All4 Staff 

On November 2, 2016, the United States Environmental Protection Agency (U.S. EPA) proposed an implementation of the 2015 National Ambient Air Quality Standard (NAAQS) for ozone (2015 ozone NAAQS) with requirements that would apply to states with nonattainment areas and states in the ozone transport region (OTR).  The proposed rule, which was subsequently published in the Federal Register (FR) on November 17, 2016, largely resembles the implementation rule promulgated for the 2008 ozone NAAQS and establishes the framework for U.S. EPA, state, tribes, and local air quality agencies for planning to achieve the 2015 ozone standards1. The three key features of the proposed rule which might impact you are as follows:

Nonattainment Area Classification

The proposed rule establishes the new nonattainment area classification thresholds for designation purposes.  The rule also sets the deadlines for areas to attain the 2015 ozone NAAQS.  The new classification thresholds and number of nonattainment areas potentially subject to each classification (based on 2013-2015 ambient air monitoring data) are as follows:


Threshold Value
(8-hr Design Value in
parts per billion)

Potential Nonattainment Areas in Each Classification


From 71 up to 81



From 81 up to 93



From 93 up to 105


Severe – 15

From 105 up to 111


Severe – 17

From 111 up to 163



Equal to or above 163


Based on this new proposed classification, there will be a total of 47 areas classified as marginal nonattainment areas with a potential 3-year attainment date (i.e. attainment by year 2020).

Nonattainment NSR Offset Requirements

Pursuant to 40 CFR Part 51.165 and 40 CFR Part 51 Appendix S, air agencies can issue a permit to a new or modified major stationary source located in an ozone nonattainment area provided that the nonattainment New Source Review (NNSR) emissions offset requirements are met.  Specifically, when NNSR air permitting occurs in ozone non-attainment areas, project-related emissions increase of volatile organic compounds (VOC) and nitrogen oxides (NOX) must be offset.  IPT regulates how these VOC and NOX emissions (i.e., ozone precursors) are offset and how offsets of one precursor pollutant can be substituted for another precursor pollutant (i.e., inter-precursor trading – IPT).   However, as part of the proposed rule, U.S. EPA plans to revise the NNSR offset requirements by requiring technical justification for the use of IPT to meet the NNSR offset requirements.  This update to the previously finalized rule is as a result of a petition for reconsideration filed by a coalition of environmental and health advocate groups.

The U.S. EPA is proposing that state, local, and tribal air agencies demonstrate that the use of IPT provides equivalent or greater air quality benefits for ozone concentration reductions in the ozone nonattainment areas as part of the implementation plan submitted by the respective agency.  U.S. EPA is proposing to allow the respective agencies to apply IPT provisions on a case-by-case basis when permitting NNSR projects.  Accordingly, each permit applicant for a NNSR project who wishes to use ozone IPT to satisfy the NNSR emissions offset requirement would be required to calculate how much one ozone precursor (e.g., VOC) would need to be offset by the other ozone precursor (NOX) in order to be equivalent.  The development of this IPT ratio would require the permit applicant to perform photochemical modeling or other technical demonstrations.  U.S. EPA included a Technical Guidance Document (TGD) on demonstration of IPT for ozone to assist stakeholders.  The TGD is available in the docket for this proposed ozone implementation rule.  ALL4 can assist you in reviewing the TGD, analyze the impact of on your potential NNSR project, and can also support you in drafting comments on the regulations.  Detailed discussion on the TGD and its implementation will be discussed in a separate blog.

Revoking the 2008 Ozone NAAQS

Last but not least, the proposed rule provides two options for revoking the 2008 ozone NAAQS as follows:

Option 1 will revoke the 2008 NAAQS in all areas one year after the 2015 ozone NAAQS designations are finalized.  Considering that the U.S. EPA is required to finalize the 2015 designations by October 2017 which will go into effect by December 2017 (60 days after publishing in FR), the 2008 NAAQS can be revoked as early as December 2018.  This option, however, will require that the air quality agencies establish anti-backsliding measures if the areas were classified as nonattainment for both the 2008 and 2015 NAAQS.

Option 2 will revoke the 2008 NAAQS only in the areas that will be designated as attainment for the 2008 NAAQS one year after the effective date of the designations for each area for the 2015 ozone NAAQS.  That is, only the areas designated as attaining the 2015 ozone NAAQS by December 2018 will be allowed to revoke the 2008 NAAQS by December 2018, but not any earlier.  For the rest of the areas, the 2008 NAAQS will continue to apply until the area can be re-designated as attainment for the 2015 ozone NAAQS.

The finalization of this proposed rule is anticipated to have impact on our clients not only because State Implementation Plans (SIPs) will be changed but also because the NNSR permitting process will be affected.  The comments on this proposed implementation rule are due to U.S. EPA by January 17, 2017.  Stay tuned for my next blog on the Technical Guidance Document on the development of IPT ratios.

[1] Federal Register 81276, published on November 17, 2016


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