EPA Administrator Zeldin Proposes Approving Another Innovative Plan in Maricopa County to Help Manufacturing and Economic Growth While Ensuring Clean Air
WASHINGTON – Today while in Maricopa County, Arizona, U.S. Environmental Protection Agency (EPA) Administrator Lee Zeldin announced the proposed approval of a second innovative air quality rule by Maricopa County to support Arizona’s continued economic expansion while maintaining clean air for the region. Administrator Zeldin was joined by U.S. Representative Andy Biggs (R-AZ-05) and a number of state and Maricopa County officials for the announcement. If finalized as proposed, the County’s Air Quality Rule 204, “Emission Offsets Generated by Voluntary Nonroad Engine Emission Reductions,” would allow key American industries, like high-tech manufacturing and power plants in the area, to use emission reduction credits (ERCs) from voluntary nonroad engine emissions reductions to build and expand production without increasing emissions.
In April 2026, EPA proposed approval of a similar Maricopa County rule covering ERCs from on-road vehicles. Through these proposals, the Trump EPA is proving once again that there does not have to be a binary choice between protecting the environment and growing the economy.
“State and local officials know what works for their communities better than anyone else,” said EPA Administrator Zeldin. “The Trump EPA is proud to work once again with Maricopa County to ensure economic growth while also protecting clean air. We can and will grow the American economy while fulfilling our core mission of protecting human health and the environment”
Portions of Maricopa County are currently designated as “Moderate” nonattainment for the 2015 Ozone National Ambient Air Quality Standards (NAAQS). As a result, major stationary sources, including power plants and manufacturing facilities, must obtain a preconstruction permit from the Maricopa County Air Quality Department (MCAQD) and offset any increase in emissions, per Clean Air Act (CAA) requirements, to build or expand in this nonattainment area.
If today’s proposed rule is finalized, nonroad engine owners and operators that permanently reduce nitrogen oxide or volatile organic compound emissions will be able to trade those reductions as ERCs to stationary sources wishing to build or expand in the County’s nonattainment area. Historically, ERCs have only been generated and traded between stationary sources; however, EPA is proposing that Rule 204 meets statutory requirements under CAA section 173. The ERCs will enable key industries to meet the manufacturing and energy needs of the area while following all CAA requirements for a “Moderate” nonattainment area for the 2015 Ozone NAAQS. EPA does not expect this rule to increase emissions in the area.
Under the framework of cooperative federalism, the Trump EPA believes that its local and state regulatory partners are oftentimes best positioned to understand the unique needs of their regions. Rule 204 provides a market-based regulatory structure that meets the area’s economic and environmental needs. EPA is proud to work with Maricopa County and Arizona to promote prosperity while fulfilling the agency’s core mission of protecting human health and the environment.
The agency will hold a 30-day public comment period. EPA’s proposed approval of Rule 204 is available here.
Background
Under the CAA, EPA established the 2015 Ozone NAAQS at 70 parts per billion.
On March 23, 2026, EPA finalized a determination not to reclassify the Phoenix-Mesa area from “Moderate” to “Serious” nonattainment under the 2015 NAAQS. Citing Section 179B of the CAA, EPA found that the Phoenix-Mesa area would have met federal ozone air quality standards by its August 3, 2024, deadline had it not been for emissions coming to the area from outside the U.S. The agency’s decision will ensure that manufacturers and citizens in the Phoenix-Mesa area are not punished for emissions out of their control.
Learn more about the CAA and NAAQS.