Air Toxics Regulatory Update

During the previous administration, we saw a flurry of revisions to air toxics regulations under 40 CFR Part 63. The United States Environmental Protection Agency (U.S. EPA) revised several National Emission Standards for Hazardous Air Pollutants (NESHAP) to include standards for additional hazardous air pollutants (HAP), additional emissions sources, and more stringent requirements for sources of ethylene oxide. Several sectors were affected by significant rule changes including coke ovens, integrated iron and steel, tire manufacturing, lime manufacturing, taconite ore processing, copper smelting, and chemical manufacturing. Under the current administration and according to various press releases, the pendulum has shifted towards regulatory reform and deregulation. In March 2025, the current administration signaled that they will reconsider each of the above referenced NESHAP and encouraged the use of an existing Clean Air Act mechanism under Section 112(i)(4) to request a two-year compliance extension via a presidential waiver. U.S. EPA has already issued a 90-day administrative stay of the 2025 compliance dates in the integrated iron and steel NESHAP, signaling a pending proposed reconsideration rule.

U.S. EPA also announced their intention to reconsider air toxics and other regulations that impact the utility sector. Almost 50 power plants recently received a two-year extension of compliance with the more stringent Mercury and Air Toxics Standards (MATS) limits. Four executive orders were issued in April that are geared toward promoting coal-fired power generation. While U.S. EPA had been working on updates to the combustion turbine NESHAP, it is not likely that we will see that proposal while they are working on the long list of items that the current administration wishes to reconsider, given the focus on deregulation instead of new requirements.

In addition, U.S. EPA is conducting a review of the brick and clay products manufacturing NESHAP under section 610 of the Regulatory Flexibility Act to determine whether the rule should continue unchanged, be amended, or be withdrawn. The following factors will be considered: (1) The continued need for the rule; (2) the nature of complaints or comments received concerning the rule; (3) the complexity of the rule; (4) the extent to which the rule overlaps, duplicates, or conflicts with other federal, state, or local government rules; and (5) the degree to which the technology, economic conditions or other factors have changed in the area affected by the rule. Comments must be received on or before May 30, 2025. It will be interesting to see whether the review results in any changes, especially given the complicated history of the rule.

Before all the announcements by the current administration, we had expected to see proposed changes to the NESHAP for industrial boilers and process heaters (Subpart DDDDD) in 2025 to address a recent court decision regarding the 2022 changes to the standards for new sources. However, this is not likely a priority given the resources available and the extended list of deregulatory actions announced in the last few months. Hopefully U.S. EPA will provide some guidance on the appropriate emissions limits for boilers constructed between June 4, 2010 and August 24, 2020.

One of the last regulatory actions released around the time of the administration change was a proposal to update the Chemical Manufacturing Area Source (CMAS) air toxics rule. The comment deadline for that rule got extended along with other proposed actions that were issued late in the previous administration. This proposal was interesting because U.S. EPA does not typically perform a risk review for area source standards, but the proposed CMAS updates included more stringent standards for ethylene oxide as a result of the risk assessment. The comment period recently closed and the final rule is due to be signed by January 15, 2026.

One thing to watch for with the announced NESHAP reconsideration actions and the final CMAS rule is a revised approach from U.S. EPA with respect to the Louisiana Environmental Action Network (LEAN) court decision that resulted in the gap-filling actions we have seen for NESHAP rules since mid-2020. In the gap-filling rules that we’ve seen since the LEAN decision, the agency has included many new requirements for additional HAP and additional equipment, even where the results of the residual risk review were acceptable and additional controls are not cost effective. Will either U.S. EPA or the court determine that additional standards should only be established if they are necessary to address risk and/or are cost effective to implement? How will the record for these rules reflect the change in interpretation? Will U.S. EPA simply invoke President Trump’s April 9 order to repeal rules that do not comport with recent decisions from the Supreme Court of the United States (SCOTUS)?

There are many questions surrounding the current air toxics-related activities announced and being undertaken by U.S. EPA. One of those is what will get done with a reduced budget? The regulated community is also wondering what changes will be durable. Will the next administration simply put all the rescinded requirements back into place? Will the court determine that certain deregulatory actions that U.S. EPA undertakes are illegal?

What should industry be doing? Follow what’s happening, evaluate the impacts of changes, decide what is important to your company and sector, engage with your industry association, and participate in the public comment process. ALL4 is monitoring U.S. EPA air toxics regulatory activity and can help you or your industry association develop technical comments on regulatory proposals or evaluate impacts of rule revisions on your facility or industry. Please contact your ALL4 project manager or Amy Marshall for assistance.