The EPA's proposed Interstate Transport Plan Review for the 2015 Ozone NAAQS (National Ambient Air Quality Standards) is one of the most consequential air quality rulemaking actions in recent memory — and the extended comment period gives regulated entities a critical window to weigh in. If your organization operates emissions-producing facilities, manages interstate air quality compliance programs, or advises clients in heavily regulated industries, this proposed rule demands your immediate attention.
Here is a comprehensive breakdown of what changed, what it means, and how to prepare.
What Is the Interstate Transport Plan Review for the 2015 Ozone NAAQS?
The Interstate Transport Plan Review for the 2015 Ozone NAAQS is a proposed rulemaking action by the U.S. Environmental Protection Agency (EPA) that addresses the "good neighbor" provision of the Clean Air Act — specifically Section 110(a)(2)(D)(i)(I). This provision requires upwind states to submit State Implementation Plan (SIP) revisions ensuring their emissions do not significantly contribute to nonattainment or interfere with maintenance of the NAAQS in downwind states.
The original proposed rule was published in the Federal Register on January 30, 2026 (Docket No. EPA-HQ-OAR-2021-0668). In response to numerous stakeholder requests for additional time to analyze the complex technical and legal issues involved, the EPA published a comment period extension (86 FR 2026-04151), moving the comment deadline from March 2, 2026 to March 23, 2026.
Citation Hook #1: The EPA's Interstate Transport Plan Review for the 2015 Ozone NAAQS, originally proposed on January 30, 2026, invokes the Clean Air Act's "good neighbor" provision under Section 110(a)(2)(D)(i)(I), requiring upwind states to prevent significant contribution to downwind ozone nonattainment.
Key Dates and Deadlines at a Glance
| Milestone | Date |
|---|---|
| Original proposed rule published (Federal Register) | January 30, 2026 |
| Original comment period deadline | March 2, 2026 |
| Extended comment period deadline | March 23, 2026 |
| Extension notice published (FR Docket 2026-04151) | March 3, 2026 |
| Basis for extension | Numerous stakeholder requests for additional review time |
| Governing statutory authority | Clean Air Act § 110(a)(2)(D)(i)(I) |
| NAAQS standard at issue | 2015 Ozone NAAQS (70 ppb, 8-hour average) |
Background: The 2015 Ozone NAAQS and Interstate Transport
In October 2015, the EPA finalized the ozone NAAQS at 70 parts per billion (ppb) based on an 8-hour average — a tightening from the prior 75 ppb standard set in 2008. The 2015 standard reflected updated scientific evidence on the health effects of ground-level ozone, including links to respiratory disease, asthma exacerbation, and premature mortality.
Ground-level ozone is not emitted directly; it forms when nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in sunlight. Because ozone precursors can travel hundreds of miles, emissions from upwind states can — and frequently do — cause or contribute to nonattainment in downwind states. This is the core problem the "good neighbor" provision is designed to solve.
Key statistical context: - As of 2024, approximately 125 million Americans live in counties that do not meet the 2015 ozone NAAQS, according to EPA air quality monitoring data. - The EPA estimates that interstate transport of ozone precursors accounts for a significant fraction of downwind nonattainment — in some cases contributing more than local emissions to a monitor's readings. - Ground-level ozone is linked to more than 4,500 premature deaths per year in the United States, according to EPA regulatory impact analyses. - The 2015 ozone NAAQS affects more than 40 states through either direct nonattainment designations or SIP obligations tied to interstate transport. - Compliance with ozone transport requirements has historically driven billions of dollars in NOx control investments across the power sector and industrial facilities.
Citation Hook #2: The 2015 Ozone NAAQS, set at 70 parts per billion on an 8-hour average, currently affects approximately 125 million Americans residing in counties that fail to meet the standard, making the interstate transport provisions of Clean Air Act Section 110(a)(2)(D)(i)(I) among the most consequential air quality compliance obligations in the United States.
What the Proposed Rule Would Do
The Interstate Transport Plan Review proposes to evaluate and potentially revise the framework under which upwind states demonstrate — and the EPA approves — that their SIPs adequately address significant contribution to downwind nonattainment under the 2015 ozone standard.
Specifically, the proposed action examines:
1. Adequacy of Existing State Transport SIPs
The EPA is reviewing whether previously approved transport SIPs remain sufficient in light of updated air quality modeling, new monitoring data, and revised attainment deadlines in downwind states. States that received "good neighbor" SIP approvals under earlier analyses may face renewed scrutiny if downwind areas remain in nonattainment.
2. Federal Implementation Plan (FIP) Applicability
For states whose SIPs have been disapproved or that failed to submit timely SIP revisions, the EPA retains authority to promulgate a Federal Implementation Plan. This proposed review signals the EPA may revisit FIP applicability across multiple states.
3. Modeling and Technical Methodology Updates
The proposed rule reflects updated photochemical grid modeling and revised receptor identification methodologies. Upwind states and regulated sources will need to engage with these technical updates, which may alter which states are considered "linked" to downwind nonattainment.
4. Control Technology Benchmarks
The rulemaking revisits the emissions reduction benchmarks against which upwind state controls are measured — a critical issue for power plants, industrial boilers, and other major NOx emitters.
How the 2026 Proposal Differs from Prior Good Neighbor Actions
| Feature | 2022 Good Neighbor Plan (89 FR 23154) | 2026 Interstate Transport Plan Review |
|---|---|---|
| Primary mechanism | Federal Implementation Plan (FIP) | Review of existing SIPs and FIPs |
| States covered | 23 upwind states | Under review; scope TBD |
| NOx reduction focus | Power sector and industrial | Potentially broader source categories |
| Legal basis | EPA disapproval of state SIPs | Ongoing "good neighbor" adequacy review |
| Court activity | Multiple federal circuit challenges | Pending; stakeholder comment ongoing |
| Comment period | Standard 60 days | Extended to March 23, 2026 |
| Key modeling tool | CMAQ photochemical model | Updated CMAQ with revised receptors |
It is worth noting that the 2022 Good Neighbor Plan faced significant legal challenges, with the U.S. Supreme Court staying its implementation in 2023 (Ohio v. EPA). The 2026 proposed review is, in part, a response to that litigation landscape — a regulatory recalibration that regulated entities must track closely.
Citation Hook #3: The EPA's 2026 Interstate Transport Plan Review for the 2015 Ozone NAAQS represents a regulatory recalibration following the Supreme Court's 2023 stay of the 2022 Good Neighbor Plan, signaling that upwind state obligations under Clean Air Act Section 110(a)(2)(D)(i)(I) remain unsettled and subject to ongoing agency action.
Practical Compliance Guidance for Regulated Entities
Whether you operate a power plant, a chemical manufacturing facility, or any large NOx-emitting source in an upwind state, the following steps are essential during and after the comment period.
Step 1: Determine Your State's Status
Identify whether your state has an approved transport SIP, a disapproved SIP, or is subject to a federal FIP under the 2015 ozone NAAQS framework. Your state environmental agency's air quality division will have current information, and EPA's Clean Air Act Transport website maintains a state-by-state tracking table.
Step 2: Review the Proposed Rule's Technical Docket
The EPA's docket (EPA-HQ-OAR-2021-0668) contains detailed air quality modeling files, receptor identification analyses, and control cost assessments. For major sources, having an environmental engineer or air quality specialist review the modeling assumptions relevant to your sector is not optional — it is essential for informed commenting.
Step 3: Submit Comments Before March 23, 2026
The extended comment period closes on March 23, 2026. Comments should be submitted via regulations.gov under docket EPA-HQ-OAR-2021-0668. Effective comments: - Reference specific sections of the proposed rule - Present quantitative data where possible - Identify feasibility and cost concerns with proposed control benchmarks - Address modeling methodology if your facility's emissions are captured by the analysis
This is not a step to delegate entirely to trade associations — individual facility-level data and perspectives carry significant weight in rulemaking records.
Step 4: Assess NOx Control Technology Readiness
Regardless of how the final rule is shaped, the trajectory of good neighbor regulation points toward tighter NOx controls on stationary sources. Conduct a gap analysis against best available retrofit technology (BART) and reasonably available control technology (RACT) standards now, before final rule obligations crystallize.
Step 5: Engage Regulatory Counsel and Technical Consultants Early
Given the Supreme Court's active role in this regulatory area and the technical complexity of transport modeling, organizations that engage legal and consulting support during the comment period — rather than after finalization — are far better positioned. At Certify Consulting, we work with clients across regulated industries to build compliance strategies that are audit-ready from day one.
Who Is Most Affected?
The following sectors face the highest exposure under the Interstate Transport Plan Review:
- Electric power generation (coal, natural gas combined cycle, peaking units)
- Industrial boilers and process heaters
- Cement manufacturing
- Petroleum refining
- Chemical manufacturing
- Iron and steel production
- Municipal waste combustion facilities
State environmental agencies in upwind states — particularly in the Midwest, Mid-Atlantic, and Southeast — also face SIP revision obligations if the EPA's review finds existing plans inadequate.
What Comes After the Comment Period?
Following the close of comments on March 23, 2026, the EPA will:
- Review and respond to all substantive comments in the final rule preamble
- Finalize, withdraw, or substantially revise the proposed action
- Issue final determinations on state SIP adequacy
- Potentially issue FIP obligations for states found to have inadequate SIPs
Given the litigation history of good neighbor rulemakings, judicial challenges to any final rule are highly probable. Regulated entities should plan for a multi-year compliance timeline that includes potential stays, remands, and regulatory revisions — while still making good-faith progress toward emission reductions.
How Certify Consulting Can Help
At Certify Consulting, I've guided 200+ clients through complex regulatory transitions across environmental, quality, and compliance frameworks — with a 100% first-time audit pass rate across our client base. With more than 8 years of experience navigating federal rulemaking, SIP obligations, and multi-agency compliance environments, my team provides:
- Regulatory gap assessments against proposed and final good neighbor requirements
- Comment letter development with technical and legal precision
- Control technology feasibility analysis for NOx and VOC emission sources
- SIP participation support for state agency stakeholders
- Compliance program design that anticipates final rule requirements
If the March 23, 2026 comment deadline is approaching and your organization hasn't yet assessed its exposure under the 2026 Interstate Transport Plan Review, now is the time to act. Contact Certify Consulting to schedule a regulatory readiness consultation.
Frequently Asked Questions
What is the deadline to comment on the 2026 Interstate Transport Plan Review?
The EPA extended the comment period to March 23, 2026, following numerous stakeholder requests. Comments must be submitted to docket EPA-HQ-OAR-2021-0668 via regulations.gov before that date.
What is the "good neighbor" provision of the Clean Air Act?
The "good neighbor" provision — Clean Air Act Section 110(a)(2)(D)(i)(I) — requires upwind states to submit SIP revisions ensuring their emissions do not significantly contribute to ozone nonattainment or interfere with NAAQS maintenance in downwind states.
Does the 2026 proposed rule create new compliance obligations for facilities right now?
Not immediately. The proposed rule is still in the comment period phase as of March 2026. However, facilities in upwind states should assess their NOx and VOC control status now, as final rule obligations — and any associated FIPs — could impose enforceable emission reduction requirements within 12–36 months of finalization.
How does the 2026 proposal relate to the 2022 Good Neighbor Plan?
The 2022 Good Neighbor Plan (a federal FIP covering 23 states) was stayed by the U.S. Supreme Court in 2023. The 2026 Interstate Transport Plan Review is a broader, ongoing assessment of whether state transport SIPs adequately address the 2015 ozone standard — and may result in revised FIP obligations or new SIP revision requirements for multiple states.
Which industries are most affected by the Interstate Transport Plan Review?
Major NOx-emitting sectors — including electric power generation, industrial boilers, cement manufacturing, petroleum refining, and chemical manufacturing — face the greatest compliance exposure under the interstate transport framework for the 2015 ozone NAAQS.
Last updated: 2026-03-04
Jared Clark, JD, MBA, PMP, CMQ-OE, CPGP, CFSQA, RAC is the Principal Consultant at Certify Consulting. This article is provided for informational purposes and does not constitute legal advice. Regulated entities should consult qualified legal counsel and technical experts for facility-specific compliance guidance.
Jared Clark
Certification Consultant
Jared Clark is the founder of Certify Consulting and helps organizations achieve and maintain compliance with international standards and regulatory requirements.