Air Plan Approval; Arizona; Yuma 2015 8-Hour Ozone Nonattainment Area; Redesignation Request and Maintenance Plan

SUPPLEMENTARY INFORMATION:

Throughout this document, “we,” “us,” and “our” refer to the EPA.

Table of Contents

I. Background

A. The 2015 Ozone National Ambient Air Quality Standards

B. The Yuma Area and Regulatory Actions

C. CAA and Regulatory Requirements for Redesignations and Maintenance Plans

II. Submissions From the State of Arizona To Redesignate the Yuma Area to Attainment for the 2015 Ozone NAAQS

A. Summary of State Submissions

B. CAA Procedural Requirements for Adoption and Submission of SIP Revisions

III. Evaluation of Arizona's Redesignation Request for the Yuma Area

A. Evaluation of Whether the Yuma Area Has Attained the 2015 Ozone NAAQS

B. The Area Must Have a Fully Approved SIP Meeting the Requirements Applicable for the Purposes of Redesignation Under Section 110 and Part D of the CAA

C. The Area Must Show That the Improvement in Air Quality Is Due to Permanent and Enforceable Emissions Reductions

D. The Area Must Have a Fully Approved Maintenance Plan Under CAA Section 175A

IV. Proposed Action and Request for Public Comment

V. Statutory and Executive Order Review

I. Background

A. The 2015 Ozone National Ambient Air Quality Standards

Ground-level ozone pollution is formed from the reaction of volatile organic compounds (VOC) and oxides of nitrogen (NO_X) in the presence of sunlight. These two pollutants, referred to as ozone precursors, are emitted by many types of sources, including on- and nonroad motor vehicles and engines, power plants and industrial facilities, and smaller area sources such as lawn and garden equipment and paints.

Scientific evidence indicates that adverse public health effects occur following exposure to ozone, particularly in children and adults with lung disease. Breathing air containing ozone can reduce lung function and inflame airways, which can increase respiratory symptoms and aggravate asthma or other lung diseases.

Under section 109 of the Act, the EPA promulgates NAAQS for pervasive air pollutants, such as ozone. The NAAQS are concentration levels the EPA has determined to be requisite to protect public health and welfare. On February 8, 1979, the EPA established primary and secondary NAAQS for ozone at 0.12 parts per million (ppm) averaged over a 1-hour period. On July 18, 1997, the EPA revised the primary and secondary standards for ozone to set the acceptable level of ozone in the ambient air at 0.080 ppm averaged over an 8-hour period (“1997 ozone NAAQS”).

In 2008, the EPA lowered the 8-hour ozone NAAQS to 0.075 ppm (“2008 ozone NAAQS”) to revise the 1997 ozone NAAQS. Then, in 2015, the EPA lowered the primary and secondary 8-hour ozone NAAQS to 0.070 ppm (“2015 ozone NAAQS” or “standard” ). Most recently, in December 2020, the EPA finalized review of the ozone NAAQS, retaining the form and level of the standards. As a result, no new ozone area designations were triggered under the CAA, and therefore, no new nonattainment area requirements will apply. This action pertains to only the 2015 ozone NAAQS.

B. The Yuma Area and Regulatory Actions

Following promulgation of a new or revised NAAQS, the EPA is required by the CAA to promulgate designations for areas throughout the U.S. in accordance with section 107(a)(1) of the CAA. Effective August 3, 2018, the EPA established the initial air quality designations for most areas in the United States for the 2015 ozone NAAQS. The EPA designated the Yuma area as “Marginal” nonattainment for the 2015 ozone NAAQS based on monitoring data from 2014-2016. Areas classified as Marginal must attain the NAAQS within three years of the effective date of the nonattainment designation. The Yuma area covers 52 square miles in the Sonoran Desert region of southwestern Arizona and is adjacent to California and the international border with Mexico. In response to the designation and classification of the Yuma area as a Marginal area, Arizona submitted to the EPA revisions to its nonattainment new source review (NNSR) program. The EPA approved the revisions and determined that the NNSR program meets the applicable NNSR program requirements for areas classified as Marginal nonattainment for the 2015 ozone NAAQS. Arizona also submitted a plan titled “Marginal Ozone Plan for the Yuma Nonattainment Area” and a technical supplement which address the emissions inventory requirement in CAA section 182(a)(1) and the emissions statement requirement in CAA section 182(a)(3). The EPA approved the emissions inventory for the Yuma area on April 5, 2022, and the emissions statement on July 29, 2022.

On October 7, 2022, the EPA determined that the Yuma area attained the 2015 ozone NAAQS by August 3, 2021, the attainment deadline specified by the Act, with a design value of 0.068 ppm. The EPA relied on 2018-2020 quality-assured, certified ambient ozone data in making the determination that the Yuma area had attained the NAAQS by the applicable date.

C. CAA and Regulatory Requirements for Redesignations and Maintenance Plans

The CAA establishes the criteria that must be met for the EPA to redesignate a nonattainment area to attainment for a given NAAQS. Specifically, section 107(d)(3)(E) sets forth the following criteria: (1) the EPA must determine that the area has attained the applicable NAAQS; (2) the EPA must have a fully approved SIP for the area under CAA section 110(k); (3) the EPA must determine that the improvement in air quality is due to permanent and enforceable reductions in emissions; (4) the EPA must have fully approved a maintenance plan for the area as meeting the requirements of CAA section 175A; and, (5) the State must have met all requirements applicable to the area under section 110 and title I, part D (“part D”) of the CAA. Section 110 identifies a comprehensive list of elements that must be included in SIPs, and part D establishes the SIP requirements for nonattainment areas. Part D is divided into six subparts. The generally applicable SIP requirements for nonattainment areas are found in subpart 1 of part D, and the ozone-specific SIP requirements are found in subpart 2 of part D. The EPA provided guidance on redesignations in a document titled “State Implementation Plans; General Preamble for the Implementation of title I of the Clean Air Act Amendments of 1990,” published in the Federal Register on April 16, 1992, and supplemented on April 28, 1992 (collectively referred to herein as the “General Preamble”). The EPA issued additional guidance in two memoranda: a September 4, 1992 memorandum from John Calcagni, titled “Procedures for Processing Requests to Redesignate Areas to Attainment” (“Calcagni memo”); and a 1995 memorandum from Mary D. Nichols, titled “Part D New Source Review (part D NSR) Requirements for Areas Requesting Redesignation to Attainment” (“Nichols memo”).

The EPA's approval of a State's maintenance plan is one of the CAA prerequisites for redesignation of a nonattainment area to attainment. Section 175A of the CAA provides the general framework for a State's maintenance plans. A State's initial 10-year maintenance plan must provide for maintenance of the NAAQS for at least 10 years after redesignation and include any additional control measures necessary to ensure such maintenance. In addition, maintenance plans must contain contingency provisions necessary to assure the prompt correction of a violation of the NAAQS during the maintenance period. At a minimum, these contingency provisions must include a requirement that a State will implement all control measures contained in the nonattainment SIP prior to redesignation. Because a State's maintenance plan submittals are SIP revisions, the EPA is obligated under CAA section 110(k) to approve them or disapprove them depending upon whether they meet the applicable CAA requirements for such plans outlined above.

For the reasons described in section III of this proposal, the EPA is proposing to approve the Yuma Maintenance Plan and approve Arizona's request for redesignation of the Yuma area to attainment for the 2015 ozone NAAQS. The EPA's proposed approvals are based on our conclusion that Arizona has satisfied all the criteria under CAA section 107(d)(3)(E).

II. Submissions From the State of Arizona To Redesignate the Yuma Area to Attainment for the 2015 Ozone NAAQS

A. Summary of State Submissions

On December 27, 2023, the Arizona Department of Environmental Quality (ADEQ) submitted to the EPA its redesignation request and the Yuma Maintenance Plan as a revision to the Arizona SIP. This document addresses all of the CAA section 107(d)(3)(E) requirements for redesignating a nonattainment area to attainment for the NAAQS and includes the required maintenance plan elements. The Yuma Maintenance Plan is organized into eight chapters and two appendices. Appendix A of the Plan provides technical support for the emissions inventory, and appendix B of the Plan contains the procedural requirements and authority to implement the Yuma Maintenance Plan.

B. CAA Procedural Requirements for Adoption and Submission of SIP Revisions

CAA sections 110(a) and 110(l) require a State to provide reasonable public notice and opportunity for public hearing prior to the adoption and submission of a SIP revision to the EPA. To meet this procedural requirement, a State must include evidence that it provided adequate public notice and an opportunity for a public hearing, consistent with the EPA's implementing regulations in 40 CFR 51.102.

ADEQ's December 27, 2023 SIP submittal includes documentation of the public process conducted by ADEQ in its adoption the Yuma Maintenance Plan. On November 15, 2023, ADEQ released a draft version of the plan for public review and published a notice of public meeting to be held on December 15, 2023, to consider the adoption of the Yuma Maintenance Plan. ADEQ adopted the Yuma Maintenance Plan on December 15, 2023, following a public hearing, as documented in the public hearing presiding officer certification and public hearing transcript. Based on the documentation in the December 27, 2023 SIP submittal, ADEQ has satisfied the applicable statutory and regulatory requirements for reasonable public notice and hearing prior to adoption and submission of the Plan. Therefore, the submission of the Yuma Maintenance Plan meets the procedural requirements for public notice and hearing in CAA sections 110(a) and 110(l) and in 40 CFR 51.102.

On June 23, 2024, the Yuma Maintenance Plan became complete by operation of law pursuant to CAA section 110(k)(1)(B).

III. Evaluation of Arizona's Redesignation Request for the Yuma Area

A. Evaluation of Whether the Yuma Area Has Attained the 2015 Ozone NAAQS

1. Statutory and Regulatory Requirements

Pursuant to section 107(d)(3)(E)(i) of the CAA, for a nonattainment area to be redesignated to attainment, the EPA must determine that the area has attained the relevant NAAQS. The EPA interprets this requirement to mean that the area must have an attaining design value based on the most recently available and quality-assured air quality monitoring data, collected in accordance with the requirements of 40 CFR part 58. These requirements include quality assurance procedures for monitor operation and data handling, siting parameters for instruments or instrument probes, and minimum ambient air quality monitoring network requirements. State, local, or Tribal agencies that operate air monitoring sites in accordance with 40 CFR part 58 must enter the ambient air quality data from these sites in the EPA Air Quality System (AQS) database. These monitoring agencies certify annually that these data are accurate to the best of their knowledge, taking into consideration the quality assurance findings. Accordingly, the EPA relies primarily on AQS data when determining the attainment status of an area.

In accordance with 40 CFR part 50, appendix U, the EPA's finding of attainment of the 2015 ozone NAAQS must be based upon complete, certified data gathered at monitoring sites in the nonattainment area in accordance with 40 CFR part 58 and entered into AQS. Under 40 CFR 50.19 and in accordance with part 50, appendix U, an area meets the 2015 ozone NAAQS when the design value at each eligible monitoring site within the area is less than or equal to 0.070 ppm, based on the calculations set forth in 40 CFR part 50, appendix U.

To have a valid design value showing attainment of the ozone standard at a given monitoring site, the ambient air quality data must meet data completeness or substitution requirements for each year under consideration. The completeness requirements are met when at least 90 percent of the days in the ozone season are complete, on average, for the three-year period, with a minimum of at least 75 percent of the complete days within the ozone monitoring period in any one year. When computing whether the minimum data completeness requirements have been met, meteorological or ambient data may be sufficient to demonstrate that meteorological conditions on missing days were not conducive to concentrations above the level of the 2015 ozone NAAQS. Missing days assumed less than the level of the 2015 ozone NAAQS are counted for the purpose of meeting the minimum data completeness requirements, subject to the approval of the Regional Administrator.

2. Monitoring Network Review, Quality Assurance, and Data Completeness

ADEQ is the governmental agency with the authority and responsibilities under the State's laws for collecting ambient air quality data in the Yuma area. As a result, ADEQ submits annual monitoring network plans to the EPA. These plans document the status of ADEQ's air monitoring network, as required under 40 CFR 58.10. The EPA reviews these annual network plans for compliance with the specific requirements in 40 CFR part 58. With respect to ozone, we have found that the annual network plans submitted by ADEQ met these requirements under 40 CFR part 58, including the minimum monitoring requirements. Yuma Supersite (AQS ID No. 04-027-8011) is the only ozone monitor in the Yuma area.

In accordance with 40 CFR 58.15, ADEQ certifies annually that the previous years' ambient concentration and quality assurance data are completely submitted to AQS and that the ambient concentration data are accurate, taking into consideration the quality assurance findings. Along with the certification letters, ADEQ submits a summary of the precision and accuracy data for all ambient air quality data. The EPA's evaluations of the relevant quality assurance data are reflected in the associated AQS design value reports. These reports include a certification evaluation and concurrence (“Cert&Eval”) flag indicating the overall quality of the corresponding monitoring data. Over the period of 2021-2023, the associated Cert&Eval flag in the design value report was “Y” for the monitoring site in the Yuma area, meaning that “[t]he certifying agency has submitted a certification letter, and EPA has no unresolved reservations about data quality (after reviewing the letter, the attached summary reports, the amount of quality assurance data submitted to AQS, the quality statistics, and the highest reported concentrations).”

The Yuma area Design Value Report also included a validity indicator (“Y”) that reflects whether the design value is valid ( i.e., calculated using data that meet the applicable completeness criteria). For the purposes of this proposal, we reviewed the data for the 2021-2023 period for completeness and determined that the ozone data collected by ADEQ met the completeness criterion at the ozone monitoring site in the Yuma area.

Finally, the EPA conducts regular technical system audits (TSAs) where we review and inspect State and local ambient air monitoring programs to assess compliance with applicable regulations concerning the collection, analysis, validation, and reporting of ambient air quality data. For the purposes of this proposal, we reviewed the findings from the EPA's 2021 TSA of ADEQ's ambient air monitoring program. In Finding 4 of the 2021 TSA, the EPA noted that ADEQ did not report all valid measurement quality checks to AQS as required by the CFR. ADEQ conducted nightly zero/precision/span checks on its ozone analyzers with certified transfer standards but did not report these to AQS. In the past, the rationale for not reporting these checks was that the stability was not tracked or was questionable given the limited time for the zero/precision/span to occur, ( i.e., 11:45 p.m.-12:15 a.m.). To address this finding, as of October 2023, ADEQ has begun to submit nightly ozone precision checks to AQS. The EPA did not recommend invalidating any data from the monitoring site in the Yuma area based on this TSA.

In summary, based on the EPA's reviews of the relevant monitoring network plans, certifications, quality assurance data, and the 2021 TSA, we propose to find that the ozone data collected in the Yuma area are suitable for determining whether the area has attained the 2015 8-hour ozone NAAQS based on the most recent certified data available in AQS.

3. Evaluation of Attainment

Table 1 shows the calculated 2015 ozone design values at the Yuma Supersite monitor (AQS ID No. 04-027-8011). The data show that the monitor in the Yuma area met the 2015 ozone NAAQS in the 2020-2022 period. In addition, preliminary data for 2024 shows that the Yuma Supersite monitor is attaining the 2015 ozone NAAQS.