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Miami | Sulfur Dioxide (SO2) Nonattainment Area

County Affected:

Parts of 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 Miami, Arizona SO2 nonattainment area (NAA) 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. Freeport McMoRan, a contributor to SO2 emissions in the NAA, made numerous improvements to their Miami Operations in 2017 as a part of a $250 million expansion project to substantially reduce SO2 emissions. In 2019, EPA took final action to approve Arizona’s SIP revision for attaining the 2010 1-hour SO2 primary national ambient air quality standard (NAAQS) for the Miami SO2 NAA, effective April 11, 2019 | View Federal Register >

Some of the controls implemented at the smelter to reduce SO2 emissions include:

  • Capture of fugitive emissions from converters and anode furnaces rooflines, and routing of these to new caustic aisle scrubber
  • Routing of emissions from the anode furnace baghouse to aisle scrubber
  • Upgrade of the vent fume scrubber, and acid plant tail gas scrubber to caustic use.
  • Improvements in capture of fugitive emissions from IsaSmelt furnace feed port and matte taping
  • Stringent SO2 emission limits established to meet federal standards

Effective March 2, 2022, EPA determined that the Miami 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 January 31, 2023, revisions to the Arizona SIP that, among other elements, provide for expeditious attainment of the SO2 NAAQS in the Miami SO2 NAA by January 31, 2027.

Source of Pollutant:

  • Smelting Metal

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