Over the past year, the Maricopa County Air Quality Department (MCAQD) has been active in adopting various regulatory updates that could affect many facilities. In the last twelve months, the department has adopted a new emission offset program, revised its gasoline handling rules, finalized long-pending updates to its General Permits rule, and completed its routine annual update incorporating federal standards by reference. For facilities operating in Maricopa County, tracking these changes and determining which are relevant to a given operation can be a considerable undertaking. As we pass the midpoint of the year, we wanted to provide a chance to reflect on the rule changes adopted over the past year and outline any key takeaways.
Rule Changes Over the Past Year
- Rule 204 – Emission Offsets Generated by Voluntary Nonroad Engine Emission Reductions (adopted November 5, 2025): This rule establishes a pathway for generating Nonroad Engine Emission Reduction Credits (NERCs) through the retirement or repowering of qualifying diesel nonroad engines in captive fleets. The rule is intended to alleviate the well-documented shortage of oxides of nitrogen (NOx) and volatile organic compound (VOC) emission reduction credits available to major sources seeking to satisfy Nonattainment New Source Review offset requirements in the Phoenix-Mesa ozone nonattainment area. This rule has been referenced and discussed multiple times, including in some of our previous publications. Additional detail is also available in MCAQD’s Rule 204 program flyer.
- Rules 352 and 353 – Gasoline Cargo Tank Testing and Use, and Storage and Loading of Gasoline at a Gasoline Dispensing Facility (revised October 1, 2025): These amendments clarify that MCAQD, rather than the tank operator, conducts leak inspections, establish corrective-action schedules for identified leaks, and require annual testing by licensed representatives. EPA has since proposed to fully approve Rule 352 and conditionally approve Rule 353 into the State Implementation Plan, with a public comment period open through September 10, 2026.
- Rules 360, 370, and 371, and Appendix G (updated November 5, 2025): MCAQD’s annual update incorporating the federal New Source Performance Standards, Federal Hazardous Air Pollutant Program requirements, and Acid Rain Program provisions finalized by EPA as of the preceding July 1.
- Rule 230 – General Permits (updated June 24, 2026): MCAQD finalized updates clarifying that facilities operating under a General Permit are not also required to obtain an individual source permit, specifying which equipment or control system changes require written notice to the Control Officer, and expanding the public notice content required for Title V sources covered by a General Permit. This update is separate from the Emergency ICE General Permit document itself, which MCAQD revised this past April; additional detail is available in our previous eNews article on generator engine permitting.
Monitoring Future Rule Changes
Facilities interested in tracking MCAQD rulemaking between eNews issues may wish to consult the county’s Adopted Rules page. Each rule and appendix is listed alongside the date of its most recent revision, allowing readers to identify dates that fall after their last review as a quick way to flag changes. While this page does not indicate the specific content of a given revision, it provides an efficient first step before reviewing the rule text or the associated Notice of Final Rulemaking.
A Change in MCAQD’s Approach to HAPs Modeling
Separately, based on recent discussions with MCAQD, the County has revised its requirements for Hazardous Air Pollutants (HAP) air dispersion modeling. MCAQD has historically performed or requested dispersion modeling for facilities emitting large amounts of HAP pollutants, commonly publishing the results in the facility’s Technical Support Document (TSD) as part of the public permit record. MCAQD has discontinued this practice and going forward TSDs will no longer include this analysis or its results, based on the department’s determination that the practice lacks a clear legal or regulatory basis. This change is consistent with the county’s own rule history: Maricopa’s local HAPs program (Rule 372) and its companion Appendix H, which set forth procedures for determining ambient HAP concentrations, were both rescinded in February 2017.
This change does not affect a facility’s underlying obligation to control HAPs under Rule 370 (MCAQD’s Federal Hazardous Air Pollutant Program) or applicable federal Maximum Achievable Control Technology (MACT) standards. It does mean, however, that permit applicants and the public will no longer see an ambient HAP impact analysis included in the TSD.
Key Takeaways
Between a new emission offset program, revised gasoline handling requirements advancing toward EPA approval, routine federal updates, and a notable change in HAP modeling practice, MCAQD remains active in regulatory rulemakings and updates to historical interpretations. Trinity will continue to monitor the department’s rulemaking activity and will provide updates as further developments arise. For questions regarding how these changes may affect your Maricopa County facility, please contact Joseph Lynch in Trinity’s Phoenix office or call 602.274.2900.
