The U.S. Environmental Protection Agency (EPA) approved the Arizona Department of Environmental Quality’s (ADEQ) request to redesignate the Ajo planning area in Pima County to attainment of the EPA health standard for particulate matter of 10 microns or less (PM10) in size. EPA’s redesignation of the Ajo planning area became effective September 3, 2020.
“It is great to know that the air quality improvements over the last decade warrant the redesignation by EPA. Pima County Department of Environmental Quality (PDEQ) worked diligently with EPA and ADEQ to complete all the necessary steps to successfully move the area from nonattainment to the maintenance plan,” said Ursula Nelson, PDEQ Director. “PDEQ will be conducting inspections in Ajo to ensure continued compliance with air quality requirements.”
After months of agency collaboration, a rule specific for the Ajo PM10 Planning Area was developed and approved by all parties providing air quality control measures that will be enforced by PDEQ.
“ADEQ’s Air Quality Division worked with our partners at PDEQ, EPA and the regulated community to develop permanent emissions reduction strategies to ensure the Ajo planning area meets and will continue to maintain federal air quality standards well into the future,” said ADEQ Air Quality Division Director Daniel Czecholinski. “More people in Arizona are breathing cleaner air, as evidenced by Ajo’s redesignation to attainment.”
In May 2019, ADEQ submitted a revision to the Arizona air quality State Implementation Plan (SIP), along with a request for EPA to redesignate the Ajo nonattainment area to attainment. The years with no violations of the air quality standard, implemented control strategies, and projections of future emissions included in the plan all demonstrated the area is expected to continue to record good air quality and maintain the PM-10 standard through 2031.
“EPA is pleased to work with ADEQ and Pima County to redesignate the Ajo area to attainment,” said EPA Pacific Southwest Regional Administrator John Busterud. “Thanks to the efforts of Arizona state and local officials and the public, the residents of Ajo are now breathing cleaner, healthier air.”
Ajo is the site of a former copper smelter and mine. Emissions from those operations as well as nearby tailings and slag storage areas contributed to elevated levels of particulate matter. In 1990, EPA designated Ajo as not meeting the National Ambient Air Quality Standards for PM-10 based on recorded violations of the standards at an ambient air monitoring station in the area.