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Sulfur Dioxide (SO2) Air Quality Designations

All National Ambient Air Quality Standards (NAAQS) undergo periodic review and may be revised to reflect the latest health, environmental, and technological advances. When a new standard is promulgated or an existing standard is revised for sulfur dioxide (SO2), the first step in implementation is to determine which areas are, or are not, violating the NAAQS or are contributing to a violation of the NAAQS. During the “designation process” states submit ambient air quality monitoring data and designation recommendations, which United States Environmental Protection Agency (U.S. EPA) reviews and considers before issuing final designations. IDEM’s Map of Nonattainment Boundaries for the 2010 SO2 1-Hour Standard [ZIP] shows the current air quality designation for all counties. Following are documents relating to U.S. EPA’s air quality designations in Indiana for the SO2 NAAQS.

2010 Primary 1-Hour SO2 Standard

U.S. EPA issued air quality designations in four rounds based on air quality monitoring and modeling data. IDEM completes annual assessments for areas subject to ongoing data requirements.

Ongoing Data Requirements
  • 2021 Assessment for Ongoing Data Requirements for the 2010 Primary 1-Hour Sulfur Dioxide National Ambient Air Quality Standard (June 16, 2021) [ZIP]
  • 2020 Assessment for Ongoing Data Requirements for the 2010 Primary 1-Hour Sulfur Dioxide National Ambient Air Quality Standard (June 24, 2020) [ZIP]
  • 2019 Assessment for Ongoing Data Requirements for the 2010 Primary 1-Hour Sulfur Dioxide National Ambient Air Quality Standard (July 1, 2019) [ZIP]
  • 2018 Ongoing Data Requirements for the 2010 Primary 1-Hour Sulfur Dioxide National Ambient Air Quality Standard (June 19, 2018) [ZIP]
  • 2017 Ongoing Data Requirements for the 2010 Primary 1-Hour Sulfur Dioxide National Ambient Air Quality Standard (June 26, 2017) [ZIP]
Rounds 3 and 4 Nonattainment Designations

Round 4 was completed on December 21, 2020, for areas around sources that are subject to U.S. EPA’s SO2 Data Requirements Rule (DRR) and elected to install and operate U.S. EPA-approved ambient air quality monitors for the characterization of air quality. Round 4 designations also include areas not previously addressed by U.S. EPA in Rounds 1-3. Round 3 was completed on December 21, 2017, based on modeling conducted to characterize air quality for areas around large sources that are subject to U.S. EPA’s DRR as well as certain smaller sources identified by IDEM or U.S. EPA for further air quality characterization.

  • Documents – March 26, 2021 to December 20, 2017 [ZIP]:
    • Federal Register Notice Concerning Round 4 SO2 Designations (March 26, 2021)
    • U.S. EPA Letter Concerning Round 4 Nonattainment Boundaries for the 2010 SO2 1-Hour Standard and Technical Support Document (December 21, 2020)
    • U.S. EPA Letter Concerning Proposed Round 4 Designation Recommendations and Technical Support Document (August 13, 2020)
    • Indiana Preliminary Round 4 Designation Recommendations (April 16, 2020)
    • Indiana State Implementation Plan (SIP) Submittal of Commissioner’s Order for Indianapolis Power and Light; Petersburg Generating Station (September 18, 2019)
    • Petition for Reconsideration and Request for Agency Stay Pending Reconsideration of Final Rule Designating Huntington Township, Huntington County, Indiana, Nonattainment under Round 3 SO2 Designations (March 9, 2018)
    • Federal Register Notice Concerning U.S. EPA Round 3 SO2 Designations (January 9, 2018)
    • U.S. EPA Letter Concerning Round 3 Nonattainment Boundaries for the 2010 SO2 1-Hour Standard and Technical Support Document (December 20, 2017)
  • Documents - October 18, 2017
    • Indiana’s Response to U.S. EPA 120-Day Letter Concerning Intended Round 3 Area Designations, Transmittal Letter and Attachments A-C [ZIP]
    • Attachments D-F [ZIP]
  • Documents - August 22, 2017 to May 10, 2017 [ZIP]:
    • U.S. EPA Proposed Round 3 Designation Recommendations (August 22, 2017)
    • Federal Register Notice Concerning U.S. EPA Approval of Indiana’s SIP Submittal, Commissioner’s Order for Carmeuse Lime, Inc. (May 10, 2017)
    • Federal Register Notice Concerning U.S. EPA Approval of Indiana’s SIP Submittal, Commissioner’s Order for SABIC Innovative Plastics (May 10, 2017)
  • Documents - January 13, 2017 [ZIP]:
    • Indiana’s Preliminary Round 3 Designation Recommendations, Transmittal Letter and Attachment 1 (January 13, 2017)
      • Attachment 2
        • Enclosures 1-4 of Attachment 2
      • Attachments 3-5
  • Documents - December 27, 2016 - December 5, 2016 [ZIP]:
    • Indiana SIP Submittal of Commissioner’s Order for Carmeuse Lime, Inc. (December 27, 2016)
    • Indiana SIP Submittal of Commissioner’s Order for SABIC Innovative Plastics (December 5, 2016)
  • Documents - September 26, 2016 to January 7, 2016 [ZIP]:
    • Update to Indiana's Round 3 and 4 Designations for the 2010 Primary 1-Hour Sulfur Dioxide National Ambient Air Quality Standard and Air Quality Characterization under the Data Requirements Rule (September 26, 2016)
    • Letter Concerning Rounds 3 and 4 Designations for the 2010 SO2 1-Hour Standard and Air Quality Characterization Around Sources under the Data Requirements Rule (DRR) with Enclosure 1 (June 30, 2016)
      • Enclosures 2 and 3
    • Indiana Sources Subject to Air Quality Characterization under Round 3 Designations, Transmittal Letter and Enclosures 1 and 2 (January 7, 2016)
Round 2 Nonattainment Designations

Round 2 was completed on June 30, 2016, for modeled areas around certain large sources identified using U.S. EPA’s Air Markets Database and monitored areas designated in Round 1 with new monitored violations.

  • Documents - July 12, 2016 to March 31, 2016 [ZIP]:
    • Federal Register Notice Concerning U.S. EPA’s Round 2 SO2 Designations (July 12, 2016)
    • U.S. EPA Letter and Technical Support Document, Round 2 Nonattainment Boundaries for the 2010 SO2 1-Hour Standard, (June 30, 2016)
    • Federal Register Notice Concerning U.S. EPA’s Approval of Indiana’s SIP Submittals, Commissioner’s Orders for the A.B. Brown and Clifty Creek Generating Stations (May 6, 2016)
    • Indiana SIP Submittal of Commissioner’s Order for the A.B. Brown Generating Station (March 31, 2016)
  • Documents - March 21, 2016 to September 16, 2015 [ZIP]:
    • Indiana SIP Submittal of Commissioner’s Order for the Clifty Creek Generating Station (March 21, 2016)
    • Indiana’s Preliminary Round 2 Designation Recommendations, Transmittal Letter and Enclosures 1-3 (September 16, 2015)
Round 1 Nonattainment Designations

Round 1 was completed on July 25, 2013, for existing monitored areas showing air quality violations.

  • Documents - August 5, 2013 to May 11, 2011 [ZIP]:
    • Federal Register Notice Concerning U.S. EPA’s Round 1 SO2 Designations (August 5, 2013)
    • U.S. EPA Round 1 Nonattainment Boundaries for the 2010 SO2 1-Hour Standard, Letter and Technical Support Document (July 25, 2013)
    • Technical Addendum to Provide an Updated Response to Preliminary Designations under the 2010 National Ambient Air Quality Standard for Sulfur Dioxide (SO2) (March 28, 2013)
    • Indiana’s Response to U.S. EPA’s Proposed Designations for the 2010 1-Hour SO2 NAAQS (March 11, 2013)
    • U.S. EPA’s Response to Indiana’s Proposed Designation Recommendations and Intended Designations for the 2010 1-Hour SO2 NAAQS (February 6, 2013)
    • Technical Addendum to Provide Updated Recommendations Concerning Air Quality Designations for the 2010 1-Hour NAAQS for Sulfur Dioxide (SO2) (January 24, 2013) and Map of Recommendations
    • Technical Addendum to Provide Updated Recommendations Concerning Air Quality Designations for the 2010 1-Hour SO2 NAAQS (April 26, 2012)
  • Technical Addendum to Indiana’s Preliminary Round 1 Designation Recommendations for the 2010 1-Hour SO2 NAAQS (January 6, 2012)
  • Indiana’s Preliminary Round 1 Designation Recommendations for the 2010 1-Hour SO2 NAAQS (May 11, 2011)

Previous SO2 Standards

U.S. EPA’s Green Book provides information concerning designations under previous standards:

IDEM’s Nonattainment Status for Indiana Counties page includes additional nonattainment history.