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Hayden | Sulfur Dioxide (SO2) Nonattainment Area

County Affected:

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

Nonattainment Area Designation Date:

Aug. 5, 2013
(78 FR 47191)

Pollutant of Concern:

Sulfur Dioxide (2010 standard)


The concentration of sulfur dioxide (SO2) in the air in the Hayden, Arizona, SO2 nonattainment area (NAA) has been above federal standards for several years. ADEQ submitted a nonattainment State Implementation Plan (SIP) to U.S. Environmental Protection Agency (EPA) in March 2017. In 2018, ASARCO, a contributor to SO2 emissions within the NAA, completed numerous improvements to the Hayden copper 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

Effective Dec. 10, 2020, EPA took final action to partially approve and partially disapprove Arizona’s SIP revision for attaining the 2010 1-hour primary SO2 national ambient air quality standard for the Hayden SO2 NAA | View Federal Register >

ADEQ is currently working on a supplemental submittal to address deficiencies identified by EPA.

Effective March 2, 2022, EPA determined that the Hayden SO2 NAA failed to attain the 2010 1-hour SO2 primary NAAQS by the applicable attainment date of Oct. 4, 2018 | View Federal Register >

As a result of this determination, the State of Arizona is required to submit by Jan. 31, 2023, revisions to the Arizona SIP that, among other elements, provide for expeditious attainment of the SO2 NAAQS in the Hayden SO2 NAA by Jan. 31, 2027.

Source of Pollutant:

  • Copper smelter

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