EPA Finalizes First-of-Its-Kind Air Quality Plan to Promote Clean Air and Facilitate Economic Growth in Maricopa County
WASHINGTON – Today, U.S. Environmental Protection Agency (EPA) took a historic step by approving a first-of-its-kind air quality rule that will enable the building and expansion of manufacturing, power plants, and other critical industries without increasing emissions in Maricopa County, Arizona. Known as “Rule 205,” Maricopa County’s Air Quality Department’s innovative air regulation will unlock a new source of emission reduction credits (ERCs) for businesses to offset emissions, as is required for the area under the Clean Air Act (CAA). By providing a new avenue for businesses to be able to build in the County, while still meeting federal air requirements, EPA is working in partnership with Maricopa County to bring new economic investment and good-paying jobs to the community. The final action proves once again that there does not have to be a binary choice between protecting the environment and growing the economy.
“When states, that know their economies and environment best, come up with a creative way to grow their economies while working within environmental requirements, EPA should work with them to get it across the finish line. The Trump EPA is proud to approve this commonsense win for Maricopa County and businesses throughout the area,” said EPA Administrator Lee Zeldin. “EPA will continue to work with our regulatory partners to find ways to protect our environment while making sure regulations work under real world conditions.”
“Maricopa County has developed a practical, market-based tool that allows business to build and expand while keeping Clean Air Act protections in place,” said EPA Pacific Southwest Regional Administrator Mike Martucci. “EPA’s approval of Rule 205 reflects our commitment to working with local partners to support economic growth and protect health in Arizona.”
Portions of Maricopa County are currently designated as “Moderate” nonattainment for the 2015 Ozone National Ambient Air Quality Standard (NAAQS). As a result, major stationary sources, including power plants and manufacturing facilities, must obtain a preconstruction permit from the County and offset any increase in emissions, per the CAA, to build or expand in a nonattainment area. Today’s final action will allow mobile source owners and operators who permanently reduce nitrogen oxide or volatile organic compound emissions 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 has found that this new plan meets statutory requirements under CAA section 173 and will enable the stationary sources to meet all CAA building requirements for an area in “Moderate” nonattainment for the 2015 Ozone NAAQS. EPA does not expect this rule to increase air emissions in the area.
The Trump EPA firmly believes its local and state regulatory partners are best positioned to understand the unique needs of their regions. Through this final action, Maricopa County and Arizona have worked within federal requirements to find a unique, market-based regulatory structure that meets the area’s economic and environmental needs. Through cooperative federalism, the Trump EPA worked with Maricopa County and Arizona to promote prosperity while fulfilling the agency’s core mission of protecting human health and the environment.
Read EPA’s final approval of Rule 205.
Background
In October 2026, while in Maricopa County, Administrator Zeldin a second innovative air quality rule by Maricopa County, Rule 204, covering ERCs from nonroad engines.
On March 23, 2026, EPA finalized a determination not to reclassify the Phoenix-Mesa area from “Moderate” to “Serious” nonattainment under the 2015 NAAQS. Consistent with CAA section 179B, 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 United States.
Under the CAA, EPA established the 2015 Ozone NAAQS at 70 parts per billion.