Comment submitted by Steven Singleton

The following comment addresses the proposed rule published at 91 FR 35445 (June 11, 2026), Docket EPA-R09-OAR-2026-3664, FRL-13379-01-R9, extending the South Coast attainment date for the 2012 annual PM2.5 NAAQS from December 31, 2025 to December 31, 2030. 1. The population-exposed factor under CAA §188(e)(3) warrants an explicit finding. Section IV.F of the proposed rule states that EPA's evaluation of the discretionary §188(e) factors "focused on the nature and extent of the nonattainment area problem and the technological and economic feasibility of additional control measures." The population exposed to concentrations above the standard — a factor Congress specifically enumerated — does not receive comparable treatment in the preamble. Given that the South Coast basin includes approximately 17 million residents, and that the monitoring data EPA itself compiles in Table 2 shows the highest design values concentrated at sites historically associated with environmental justice communities (including Mira Loma, Ontario, Compton, and Long Beach), the record would benefit from an affirmative statement of who is exposed at the highest concentrations and for how long the extension leaves them there. This factor is discretionary, not mandatory, but its omission from the preamble leaves no basis in the record for evaluating the extension's distributional impact. EPA is asked to supplement the record with a demographic and exposure characterization tied to the design-value monitoring sites identified in Table 2. 2. The relationship between this extension and the pending review of the attainment demonstration should be clarified. Section IV.D states that EPA "will evaluate this analysis in a future rulemaking action," while treating the §188(e) precondition as satisfied on the basis that a demonstration was submitted. The proposed rule does not identify a docket number or expected timeline for that subsequent review. Because the extension requested is the full five-year statutory maximum, the record would be strengthened by identifying when the substantive adequacy review will occur, so the public can track whether the underlying 2030 demonstration is confirmed before the extension period elapses. 3. Interim reporting ahead of the January 1, 2030 MSM deadline would support the extension's own stated purpose. The four Most Stringent Measures identified in footnote 64 (livestock waste, greenwaste, commercial cooking, and wood-burning device requirements) were adopted in February 2026. Under the existing MSM implementation framework, they must be fully in place no later than January 1, 2030 — one year ahead of the attainment date itself. This leaves limited time between measure implementation and the deadline against which their success will be judged. EPA is asked to consider requesting or committing to an interim reporting checkpoint, such as a 2028 progress update, so that emissions performance data can inform course correction well before the extension period closes rather than only at its end. 4. Basis for selecting the full five-year extension. Footnote 65 indicates the State's own conclusion that attainment by 2029 would not be possible. Because this conclusion is part of the demonstration whose adequacy EPA has not yet substantively reviewed (see Comment 2), EPA is asked to state whether it has independently evaluated the choice of 2030 over an earlier date within the statutory window, or whether the maximum extension was granted on the basis of the State's determination alone. These comments are offered as requests for the record and questions EPA may wish to address before finalizing this action, not as objections to the extension itself.