Hayden | Sulfur Dioxide (SO2) Nonattainment Area

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Air Quality Improvement Planning

Hayden | Sulfur Dioxide Nonattainment Area

Revised On: May. 1st, 2025 - 02:55 pm

Counties Affected:

Parts of Pinal and Gila County | View on a Map >

Nonattainment Area Designation Date:

Aug. 5, 2013

Learn more about the designation of the area in the Federal Register (FR) (78 FR 47191) | View >

Pollutant of Concern:

Sulfur Dioxide (SO2) (2010 standard)

Summary: 

The concentration of SO2 in the air in Hayden has been above federal standards for several years. ADEQ submitted a nonattainment State Implementation Plan (SIP) to the U.S. Environmental Protection Agency (EPA) in March 2017. In 2018, ASARCO completed numerous improvements to the Hayden smelter as part of a $180 million converter retrofit project that has substantially reduced SO2 emissions. Some of the controls implemented at the copper smelter include:

  • Ventilation hooding over furnaces
  • Wet gas cleaning system improvements
  • High surface area lime injection system for secondary hood baghouse and furnace ventilation baghouse
  • Stringent SO2 emission limits established to meet federal standards

On May 21, 2020, EPA proposed to partially approve and partially disapprove Arizona’s SIP revision for attaining the 2010 one-hour primary SO2 National Ambient Air Quality Standard (NAAQS) for the Hayden SO2 Nonattainment Area. ADEQ is currently working on a supplemental submittal to address deficiencies identified by EPA.

On Nov. 5, 2020, EPA finalized a limited approval/limited disapproval of ADEQ’s 2017 SIP revision (85 FR 70483). On Nov. 10, 2020, EPA finalized a partial approval/partial disapproval (85 FR 71547).

On Oct. 3, 2023, ADEQ submitted a SIP revision to EPA to show attainment of the 1971 and 2010 SO2 NAAQS. This SIP revision also included a revised good engineering practice demonstration study. This SIP revision is currently pending EPA’s action. 

Rulemaking:

Learn more about the state level rulemaking to incorporate controls for the Hayden SO2 Nonattainment Area into the Arizona Administrative Code | View >

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