Sulfur Dioxide (SO2) Designation History

• 12/27/2024: EPA’s Final Rule for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen, Oxides of Sulfur, and Particulate Matter
  • Summary: "Based on the Environmental Protection Agency's (EPA's) review of the air quality criteria for ecological effects and secondary national ambient air quality standards (NAAQS) for oxides of nitrogen (N oxides), oxides of sulfur (SOX), and particulate matter (PM), the EPA is revising the existing secondary sulfur dioxide (SO2) standard to an annual average, averaged over three consecutive years, with a level of 10 parts per billion (ppb). Additionally, the Agency is retaining the existing secondary standards for N oxides and PM, without revision. The EPA is also finalizing revisions to the data handling requirements for the secondary SO2 NAAQS."
  • Final rule link: 89 FR 105692
• 12/5/2025: North Carolina's Recommendation on Boundaries for the 2024 Revised Secondary Annual Sulfur Dioxide (SO2) National Ambient Air Quality Standard
  • Designation Recommendation Letter to EPA

Designations Related to the Sulfur Dioxide (SO₂) Data Requirements Rule

• 12/21/2020 - EPA's Final Rule 4 Boundary Designations for the 2010 1-Hour Sulfur Dioxide (SO₂) National Ambient Air Quality Standard.
  • Federal Register Notice (86 FR 16055; March 26, 2021)
  • Letter from EPA to Governor Cooper and Technical Support Document (12/21/2020)
• 12/21/2017 - EPA's Final Boundary Designations for the 2010 1-Hour Sulfur Dioxide (SO₂) National Ambient Air Quality Standard.
  • Federal Register Notice
  • EPA Technical Support Document
• 10/23/2017 - State of North Carolina's Response to EPA's 120-Day Letter
  • Letter to EPA
• 8/22/2017 - EPA's 120 Day Letter Responding to NC's January 13, 2017 Boundary Recommendations
  • Letter to the NC Governor
  • Technical Support Document
• 1/13/2017  - North Carolina's Recommendation on Boundaries for the 2010 1-Hour Sulfur Dioxide (SO₂) National Ambient Air Quality Standard
  • Transmittal Letter to EPA
  • State of North Carolina's Recommendation on Boundaries For the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard
  • Attachment A - North Carolina's 2010 SO₂ NAAQS Boundary Recommendation
  • Attachment B - Maps of Modeled Facilites
  • Attachment C - Maps of Monitored Facilites
  • Attachment D - Maps of Ambient Air Quality Monitors
  • Attachment E - SO₂ Facilities and their 2015 Emissions
• 6/30/2016 -  North Carolina SO₂ Data Requirements Rule Air Quality Characterization Submittal
  • Air Quality Characterization via Modeling – Modeling Reports
    • Transmittal to EPA
    • Duke Energy Progress Belews Creek Generating Station
    • Duke Energy Progress Marshall Steam Station
    • Duke Energy Progress Mayo Electric Generating Electric Plant
    • Duke Energy Allen Steam Station
  • Air Quality Characterization via Modeling – Modeling Protocols
    • Duke Energy Carolinas, LLC – Allen Steam Station
    • Duke Energy Progress, Inc. – Asheville Steam Electric Plant
    • Duke Energy Progress, LLC – Mayo Facility
    • Duke Energy Carolinas, LLC – Marshall Steam Station
    • Duke Energy Carolinas, LLC – Belews Creek Steam Station
  • Air Quality Characterization via Monitoring  –
    Plans for characterization of air quality via monitoring for the following facilities are included in North Carolina’s Annual Monitoring Network Plan:
    • PCS Phosphate Company, Inc. - Aurora
    • CPI USA North Carolina – Southport Plant
    • Blue Ridge Paper Products – Canton Mill
    • Duke Energy Progress, LLC – Roxboro Plant
• 3/18/2016 - EPA response to NC's Facilities in North Carolina Subject to the SO2 Data Requirements Rule
• 1/15/2016 - Facilities in North Carolina Subject to the SO₂ Data Requirements Rule

Designations for Brunswick County

• 9/28/2021 – USEPA Final Rule:  Redesignation of the Brunswick County 2010 Sulfur Dioxide Unclassifiable Area (86 FR 53555)
• 7/2/2021 – USEPA Proposed Rule:  Air Quality Designations; NC: Redesignation of the Brunswick County 2010 Sulfur Dioxide Unclassifiable Area (86 FR 35254)
• 4/23/2021 – Redesignation Request for Brunswick County for the 2010 1-Hour Sulfur Dioxide Primary NAAQS
• 6/30/2016 – EPA’s second round of SO₂ designations
  • EPA designation letter for Brunswick County, 6/30/16
  • EPA Technical Support Document for Brunswick County, 6/30/16
• 4/19/2016 - North Carolina's Updated Boundary Recommendations for Brunswick County and New Hanover County
  • Attachment: CPI Southport Permit, issued 4/18/2016
  • 2/16/2016 - EPA Response (120-day letter) and Technical Support Document
  • 9/18/2015 - North Carolina's Boundary Recommendations for Brunswick County and New Hanover County

Initial Statewide Boundary Recommendations

• 4/8/2013 - North Carolina's Recommendations for Air Quality Designations for the Sulfur Dioxide Standard
• 6/2/2011 - North Carolina SO₂ Boundary Recommendation
• 4/12/2011 - North Carolina SO₂ Draft Boundary Options (pdf)

Implementation

• EPA's SO₂ Implementation Guidance
• 7/14/2014 - NCDAQ's Comments on USEPA's Data Requirements Rule for the 1-Hour SO₂ Standard
• 6/29/2012 - NCDAQ's Comments on USEPA's Proposed SO₂ Implementation

2010 1-hour SO₂ Standard

• 6/22/2010 - EPA's Final 1-hour SO₂ NAAQS Rule
• 12/8/2009 - NCDAQ's Comments on USEPA's Proposed SO₂ Standard