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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 SO2 in the air in Hayden has been above federal standards for several years. ADEQ submitted a nonattainment State Implementation Plan (SIP) to 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 the EPA proposed 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 nonattainment area. ADEQ is currently working on a supplemental submittal to address deficiencies identified by EPA.

Source of Pollutant:

  • Copper smelter

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