EPA Proposes Approving Maricopa County’s Innovative Emission Reduction Credits Plan for Facilities to Grow the Economy While Ensuring Clean Air
WASHINGTON – U.S. Environmental Protection Agency (EPA) is proposing to approve Maricopa County’s innovative air quality 205 rule, “Emission Offsets Generated by Voluntary Mobile Source Emission Reductions”, to support Arizona’s economic expansion while maintaining clean air for the region. If finalized as proposed, key American industries like high-tech manufacturing and power plants in Maricopa County will be able to utilize much-needed emission reduction credits (ERCs) from voluntary mobile source emissions reductions to build and expand production without increasing emissions. Through this proposal, the Trump EPA is proving once again that protecting human health and the environment, and growing the economy, is not a binary choice.
“In addition to finalizing Arizona’s international transport plan, this is another milestone in ensuring Arizona’s economy can continue to boom while also protecting air quality,” said EPA Administrator Lee Zeldin. “This proposal is another example of the Trump EPA following through on our commitment to listening to concerns and addressing issues preventing economic development in the United States while meeting our statutory requirements and fulfilling our core mission.”
“We at EPA are proud to work once again with Maricopa County to ensure that the Phoenix-Mesa area can unleash economic growth while also meeting Clean Air Act requirements to improve air quality,” said EPA Acting Region 9 Administrator Mike Martucci. “Cooperative federalism is a key pillar for the Trump EPA, and we applaud the creativity of local partners as they work towards building thriving communities.”
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 and offset any increase in emissions per the CAA to build or expand in a nonattainment area.
If EPA’s proposal is finalized as proposed, mobile source owners and operators that permanently reduce nitrous oxide (NOx) or volatile organic compound (VOC) emissions will be able to trade those reductions as ERCs to stationary sources wishing to build or expand in the County’s nonattainment areas. Historically, ERCs have only been generated and traded between stationary sources; however, EPA is proposing that the 205 rule still meets statutory requirements under CAA section 173(a). The ERCs 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 emissions in the area.
The Trump EPA believes that its state regulatory partners are best positioned to understand the unique needs of their regions. Arizona’s 205 rule provides a market-based regulatory structure that meets the area’s economic and environmental needs. EPA is proud to, through cooperative federalism, work with Arizona to promote prosperity while fulfilling the agency’s core mission of protecting human health and the environment.
EPA’s proposed approval of Rule 205 is available here. EPA is accepting public comments until May 18, 2026.
Background
Under the CAA, EPA established the 2015 Ozone NAAQS standards at 70 parts per billion to protect human health and the environment.
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 United States. 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.