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Federal Register / Vol. 86, No. 185 / Tuesday, September 28, 2021 / Proposed Rules
working in partnership with states, developed the following four-step interstate transport framework to address the requirements of the good neighbor provision for the ozone NAAQS: 1 Identify downwind air quality problems; 2 identify upwind states that impact those downwind air quality problems sufficiently such that they are considered linked and therefore warrant further review and analysis; 3 identify the emissions reductions necessary if any, applying a multifactor analysis, to prevent linked upwind states identified in step 2 from contributing significantly to nonattainment or interfering with maintenance of the NAAQS at the locations of the downwind air quality problems; and 4 adopt permanent and enforceable measures needed to achieve those emissions reductions.
The EPA has released several documents containing information relevant to evaluating interstate transport with respect to the 2015 ozone NAAQS. First, on January 6, 2017, the EPA published a notice of data availability NODA with preliminary interstate ozone transport modeling with projected ozone design values for 2023 using a 2011 base year platform, on which we requested comment.8 In the NODA, the EPA used the year 2023
as the analytic year for this preliminary modeling because that year aligns with the expected attainment year for Moderate ozone nonattainment areas for the 2015 ozone NAAQS.9 On October 27, 2017, we released a memorandum 2017 memorandum containing updated modeling data for 2023, which incorporated changes made in response to comments on the NODA, and noted that the modeling may be useful for states developing SIPs to address good neighbor obligations for the 2008 ozone NAAQS.10 On March 27, 2018, we issued a memorandum March 2018
memorandum noting that the same 2023 modeling data released in the 2017
memorandum could also be useful for identifying potential downwind air quality problems with respect to the include the NOX SIP Call, 63 FR 57356 October 27, 1998, and the Clean Air Interstate Rule CAIR, 70
FR 25162 May 12, 2005.
8 See Notice of Availability of the Environmental Protection Agencys Preliminary Interstate Ozone Transport Modeling Data for the 2015 Ozone National Ambient Air Quality Standard NAAQS, 82 FR 1733 January 6, 2017.
9 82 FR 1735 January 6, 2017.
10 See Information on the Interstate Transport State Implementation Plan Submissions for the 2008 Ozone National Ambient Air Quality Standards under Clean Air Act Section 110a2DiI, October 27, 2017, available in the docket for this action or at https www.epa.gov/
interstate-air-pollution-transport/interstate-airpollution-transport-memos-and-notices.

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2015 ozone NAAQS at step 1 of the four-step interstate transport framework.
The March 2018 memorandum also included the then newly available contribution modeling results to assist states in evaluating their impact on potential downwind air quality problems for the 2015 ozone NAAQS
under step 2 of the interstate transport framework. The EPA subsequently issued two additional memoranda in August and October 2018, providing additional information to states developing good neighbor SIPs for the 2015 ozone NAAQS concerning, respectively, potential contribution thresholds that may be appropriate to apply in step 2 of the framework, and considerations for identifying downwind areas that may have problems maintaining the standard at step 1 of the framework.11
On October 30, 2020, in the Notice of Proposed Rulemaking for the Revised CSAPR Update, the EPA released and accepted public comment on updated 2023 modeling that used the 2016
emissions platform developed under the EPA/Multi-Jurisdictional Organization MJO/state collaborative project as the primary source for the base year and future year emissions data.12 On March 15, 2021, the EPA signed the final Revised CSAPR Update using the same modeling released at proposal.13
Although Hawaii relied in part on the modeling included in the March 2018
memorandum to develop its SIP
submission, the EPA now proposes to primarily rely on the updated and newly available 2016 base year modeling in evaluating this submission.
By using the updated modeling results, EPA is using the most current and technically appropriate information as the primary basis for this proposed rulemaking. EPAs independent analysis, which also evaluated historical monitoring data, recent ambient air monitoring design values, and 11 See Analysis of Contribution Thresholds for Use in Clean Air Act Section 110a2DiI
Interstate Transport State Implementation Plan Submissions for the 2015 Ozone National Ambient Air Quality Standards, August 31, 2018 August 2018 memorandum, and Considerations for Identifying Maintenance Receptors for Use in Clean Air Act Section 110a2DiI Interstate Transport State Implementation Plan Submissions for the 2015 Ozone National Ambient Air Quality Standards, October 19, 2018, available in the docket for this action or at https www.epa.gov/
airmarkets/memo-and-supplemental-informationregarding-interstate-transport-sips-2015-ozonenaaqs.
12 See 85 FR 68964, 68981. The results of this modeling are included in a spreadsheet in the docket for this action. The underlying modeling files are available for public review in the docket for the Revised CSAPR Update EPAHQOAR
20200272.
13 82 FR 23054 April 30, 2021.

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emissions trends, found that such information provides additional support and further substantiates the results of the 2016 base year modeling as the basis for this proposed rulemaking. Section II
of this document and the Air Quality Modeling technical support document TSD included in the docket for this proposed action contain additional detail on this modeling.14
In the CSAPR, CSAPR Update, and the Revised CSAPR Update, the EPA
used a threshold of one percent of the NAAQS to determine whether a given upwind state was linked at step 2 of the interstate transport framework and would, therefore, contribute to downwind nonattainment and maintenance sites identified in step 1. If a states impact did not equal or exceed the one percent threshold, the upwind state was not linked to a downwind air quality problem, and the EPA, therefore, concluded the state would not significantly contribute to nonattainment or interfere with maintenance of the NAAQS in the downwind states. However, if a states impact equaled or exceeded the one percent threshold, the states emissions were further evaluated in step 3, to determine what, if any, emissions might be deemed significant and, thus, must be eliminated under the good neighbor provision. The EPA is proposing to rely on the one percent threshold i.e., 0.070
ppb for the purpose of evaluating Hawaiis contributions to nonattainment or maintenance of the 2015 ozone NAAQS in downwind areas.
Several D.C. Circuit court decisions have addressed the issue of the relevant analytic year for the purposes of evaluating ozone transport air-quality problems. On September 13, 2019, the D.C. Circuit issued a decision in Wisconsin v. EPA, remanding the CSAPR Update to the extent that it failed to require upwind states to eliminate their significant contribution by the next applicable attainment date by which downwind states must come into compliance with the NAAQS, as established under CAA section 181a.15
On May 19, 2020, the D.C. Circuit issued a decision in Maryland v. EPA
14 See Air Quality Modeling Technical Support Document for the Proposed Revised Cross-State Air Pollution Rule Update, 85 FR 68964 October 30, 2020, available in the docket for this action or at https www.epa.gov/csapr/revised-cross-state-airpollution-rule-update. This TSD was originally developed to support EPAs proposed action in the Revised CSAPR Update, as relating to outstanding good neighbor obligations under the 2008 ozone NAAQS. While developed in this separate context, the data and modeling outputs, including interpolated design values for 2021, may be evaluated with respect to the 2015 ozone NAAQS
and used in support of this action.
15 938 F.3d 303, 313.

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