Regulatory Roundup

On or about October 2, 2026, EPA sent what are informally called "120-day letters" to all states, the District of Columbia, territories, and certain Tribes, telling each whether it intends to modify the initial designations they submitted for the 2024 annual PM2.5 standard. The Clean Air Act requires EPA to send these notices at least 120 days before it promulgates final designations. EPA published a notice in the Federal Register on October 6 and is accepting public comments through November 5, 2026 (Docket ID EPA-HQ-OAR-2024-0078).

For final designations, EPA says it intends to rely on design values from 2023–2025 monitoring data in its Air Quality System. Where a state recommended "attainment" and EPA agrees, the agency intends to designate the area "attainment/unclassifiable," which carries the same obligations as attainment. EPA's letters also asked states to send any additional information within 30 days of receiving them.

EPA is moving forward under the July 2026 court order requiring final designations by February 6, 2027 (see the July update below). The agency notes that it is appealing that order, but is proceeding with designations in the absence of further action from the courts.

Why it matters for monitoring programs: designations are decided at the monitor level. An area meets the 2024 standard when its three-year average of annual means, the design value, is at or below 9.0 µg/m³, and EPA notes that data from a site's primary monitor and a suitable collocated FRM or FEM can be combined to establish that design value. Agencies near the line should review their 2023–2025 records, data completeness, and any pending exceptional events documentation now, ahead of the November 5 deadline.

Read the Federal Register Notice → EPA Designations Page →

On September 14, 2026, EPA Administrator Lee Zeldin signed two concurrent actions under Clean Air Act Section 111. The first is a final rule partially repealing the 2024 Carbon Pollution Standards for fossil fuel-fired electric generating units. The second is a supplemental proposal that would repeal all remaining greenhouse gas standards for the source category.

The proposal asks whether EPA has authority under Section 111 to regulate power plant greenhouse gas emissions at all. It builds on two lines of reasoning: whether those emissions "contribute significantly" to dangerous air pollution, and the agency's earlier rescission of the 2009 Endangerment Finding (see the February update below). EPA held virtual public hearings on October 1 and 2, and comments are due on or before November 2, 2026.

Why it matters for monitoring programs: like the endangerment finding rescission, this action targets greenhouse gas emission standards rather than ambient air monitoring requirements. It doesn't change criteria pollutant monitoring obligations, but it continues a broad shift in federal air priorities that's worth tracking for its effects on state programs and resources.

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Multiple outlets reported this month that federal funding for public air monitoring has failed to keep pace with rising costs, leading to reduced coverage in several long-running networks. Reporting on the IMPROVE network, which tracks visibility and haze-related pollution at national parks and wilderness areas, describes indefinite closures at some monitoring sites and reduced sample collection frequency at others, according to a former director of EPA's air quality assessment division. Cuts have reportedly been concentrated at sites where air quality is already cleanest, but observers note that closing a site removes the ability to confirm that air quality remains good there going forward.

More broadly, coverage this month notes that the number of public air monitors nationwide has declined over recent decades, that remaining equipment is often aging or located away from major pollution sources, and that legislative efforts to establish new dedicated monitoring funding introduced in both 2025 and 2026 have failed to pass Congress.

The same reporting points to evidence that additional monitoring works: after EPA required refineries to monitor benzene along facility fencelines starting in 2018, the number of refineries exceeding EPA's benzene action level dropped by roughly half within five years, according to an analysis by the Environmental Integrity Project. Some states, including California and Colorado, have stepped in with their own funding and fenceline monitoring requirements for industrial facilities.

Why it matters for monitoring programs: as public monitoring capacity comes under strain, agencies, industry, and communities looking to fill coverage gaps may increasingly turn to contract monitoring services, third-party data validation, and lower-cost portable or fenceline equipment to supplement shrinking federal networks.

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On July 1, 2026, EPA proposed revisions to the public participation requirements tied to minor New Source Review (NSR) permitting, the process states use to approve construction or modification of smaller stationary emission sources. Under the Clean Air Act, states submit implementation plans to EPA that spell out how minor NSR permitting will work, including how much public comment and hearing process is required before a permit is approved.

The proposed change would let state and local air quality agencies decide for themselves how much public participation is necessary for individual minor permits and minor modifications, rather than following a standardized federal minimum. EPA's stated rationale is reducing administrative burden on the agencies that process these permits; the change would not apply to major-source permitting, Title V operating permits, or existing SIP development requirements.

The comment period closed on August 21, 2026, after drawing significant pushback from environmental, public health, and community organizations concerned about reduced transparency for facilities near residential areas, including a rise in minor-source permits for backup diesel generators at data centers. As of early October 2026, EPA's New Source Review page still lists the action as a proposed rule; the agency is expected to review the comment record before deciding whether to finalize, revise, or withdraw it. Even where a state adopts EPA's approach, it would still need to submit and receive approval for a revised state implementation plan before existing minor NSR public participation requirements would change.

Why it matters for monitoring programs: current public participation requirements remain in effect for now. If finalized, permitting timelines and comment expectations for minor sources could begin to vary more by state, which is worth watching for programs operating across multiple states.

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When EPA tightens a National Ambient Air Quality Standard (NAAQS), like it did for PM2.5 in February 2024, the agency is legally required to designate which regions across the country meet the new standard ("attainment") and which don't ("nonattainment") within a set timeframe. Those designations determine which areas face stricter permitting, control requirements, and monitoring obligations going forward.

In Alliance of Nurses for Healthy Environments v. Zeldin, a coalition of state and local governments along with environmental and public health groups sued EPA, arguing the agency had failed to complete these designations within the legally required window following the 2024 PM2.5 standard. On July 17, 2026, the U.S. District Court for the Northern District of California agreed, ruling that EPA had not fulfilled its non-discretionary duty under the Clean Air Act to issue timely attainment designations, and ordered EPA to complete them by February 6, 2027.

Separately, on June 26, 2026, the D.C. Circuit upheld the 2024 PM2.5 standard itself in Kentucky v. EPA, rejecting challenges from industry groups, several states, and EPA's own arguments that the agency had not conducted a sufficiently "thorough review" before tightening the standard.

Update, October 2026: EPA has since sent its 120-day designation letters to the states and opened a comment period through November 5, 2026, while also appealing the district court's order. See the October update above.

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On February 12, 2026, EPA finalized a rule rescinding its 2009 Greenhouse Gas Endangerment Finding, the scientific and legal determination that underlies federal regulation of greenhouse gas emissions from motor vehicles under the Clean Air Act. The final rule, effective April 20, 2026, also repealed the associated GHG emission standards and related testing, reporting, and averaging requirements for light-, medium-, and heavy-duty vehicles and engines. EPA has described the action as the single largest deregulatory action in U.S. history.

The rescission followed a proposal issued in 2025 and drew swift legal challenges: within days of the final rule, a coalition of environmental and public health organizations filed a petition for review in the U.S. Court of Appeals for the D.C. Circuit contesting its legality. That litigation remains ongoing, and legal observers expect it could eventually reach the Supreme Court.

EPA has also continued reconsidering related Biden-era vehicle emissions rules for model years 2027 and later, including nitrogen oxide reduction requirements for heavy-duty engines under the Clean Trucks Plan, while that separate reconsideration proceeds. In September 2026, EPA cited the rescission in its proposal to repeal the remaining power plant greenhouse gas standards (see the September update above).

Why it matters for monitoring programs: this action centers on vehicle greenhouse gas emissions rather than ambient air monitoring requirements directly, and its legal fate is still being litigated. But a shift of this scale in EPA's regulatory priorities is worth watching for downstream effects on state-level funding, staffing, and attention available for ambient monitoring programs more broadly.

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