Sulfur Dioxide State Planning

The Clean Air Act regulates sulfur dioxide as a criteria pollutant. The U.S. Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards for sulfur dioxide (SO₂). These standards include both primary standards to protect public health and secondary standards to protect the environment. EPA reviews pollutant standards every five years. Sometimes, a review results in a tightened standard. The primary annual and 24-hour standards were set in 1971, along with secondary annual and 3-hour standards. The secondary annual standard was revoked in 1973, but the existing 3-hours secondary standard of 500 ppb was retained. When EPA revised the sulfur dioxide standard in 2010, they revoked the two previous primary standards, replacing them with a new 1-hour primary standard of 75 parts per billion (ppb), The form of the 1-hour standard is the 3-year average of the 99th percentile of the yearly distribution of 1-hour daily maximum SO₂ concentrations.

When EPA revised the 2010 sulfur dioxide standard, they also chose a different approach to establishing boundary designations. EPA decided to use a hybrid monitoring-modeling approach for sulfur dioxide with a series of variable designation dates based on the designation approach selected. The initial round for boundary designations was based on available ambient air quality monitoring data at the time EPA established the standard. The second round was targeted at areas surrounding facilities that had the largest annual SO₂ emissions. The third round was targeted at areas surrounding facilities with emissions more than 2,000 tons per year that elected to characterize air quality using refined dispersion modeling analyses. The fourth and final round is targeted at areas surrounding facilities with emissions more than 2,000 tons per year that elected to characterize air quality using newly deployed ambient SO₂ monitors in the areas of maximum expected SO₂ concentrations surrounding such sources.

The SO₂ standard below includes the state implementation plan elements developed for the standard and the relevant documents associated with the boundary designations for each round. If you are looking for a document that is not available on our website, please submit a Open Records/ Sunshine Law Request.

Infrastructure SIP

Infrastructure SIP Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
July 1, 2013	Section 110 Infrastructure Requirements for the 2010 Sulfur Dioxide National Ambient Air Quality Standard	Sept. 24, 2018	Air Plan Approval; Missouri; Regional Haze Plan and Prong 4 (Visibility) for the 2012 PM2.5, 2010 NO2, 2010 SO2, and 2008 Ozone NAAQS [83 FR 48242]
		March 22, 2018	Approval of Implementation Plans; State of Missouri; Elements of the Infrastructure State Implementation Plan Requirements for the 2008 Ozone, 2010 Nitrogen Dioxide, 2010 Sulfur Dioxide, and 2012 Fine Particulate Matter National Ambient Air Quality Standards (NAAQS) [83 FR 12496]

Initial Round - Existing Monitors

Initial Round: Boundary Recommendations Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
April 26, 2013	Revised Boundary Recommendation of Nonattainment and Unclassifiable Areas Per the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard	Aug. 5, 2013	Air Quality Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard [78 FR 47191] Effective: Oct. 4, 2013
July 19, 2011	2010 Sulfur Dioxide National Ambient Air Quality Standard Summary of Recommendation of Nonattainment and Unclassifiable Boundaries in Missouri	Feb. 6, 2013	EPA Response to Recommendations on 2010 National Ambient Air Quality Standard for Sulfur Dioxide - 120-day letter for the initial round designations Draft Technical Support Document: Missouri Area Designations for the 2010 SO2 Primary National Ambient Air Quality Standard

Jefferson County (Partial) Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
April 9, 2021	Maintenance Plan Supplement for the Jefferson County Nonattainment Area for the 2010 Sulfur Dioxide Standard	Jan. 28, 2022	Air Plan Approval; Missouri Redesignation Request and Associated Maintenance Plan for the Jefferson County 2010 SO2 1-Hour NAAQS Nonattainment Area [87 FR 4508]
Dec. 21, 2017	Redesignation Request and Maintenance Plan for the  2010 Sulfur Dioxide Standard Jefferson County Nonattainment Area
Feb. 2, 2016	MoDNR Determination Request for Jefferson County 2010 1-hour Sulfur Dioxide National Ambient Air Quality Standard Attainment	Sept. 13, 2017	Approval of Missouri Air Quality Implementation Plans; Determination of Attainment for the 2010 1-Hour Primary Sulfur Dioxide National Ambient Air Quality Standard; Jefferson County Nonattainment Area [82 FR 28605]
May 29, 2015	Nonattainment Area Plan for the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard: Jefferson County Sulfur Dioxide Nonattainment Area (All elements withdrawn from EPA consideration except the base year emissions inventory) MoDNR Clarification of the Redesignation Request for the Jefferson County 2010 SO2 Nonattainment Area Plan MoDNR Withdrawal Request-Nonattainment Area Plan for the 2010 1-Hour SO2 NAAQS: Jefferson County MoDNR Withdrawal Request-10 CSR 10.6261 Control of Sulfur Dioxide Emissions Rule Action	Feb. 13, 2019	Air Plan Approval; Missouri; Emissions Inventory for the Missouri Jackson County and Jefferson County 2010 Sulfur Dioxide National Ambient Air Quality Standard Nonattainment Areas [84 FR 3703]

Jackson County (Partial) Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
Sept. 3, 2021	Maintenance Plan Supplement for the Jackson County Nonattainment Area for the 2010 Sulfur Dioxide Standard	Jan. 31, 2022	Air Plan Approval; Missouri Redesignation Request and Associated Maintenance Plan for the Jackson County 2010 SO2 1-Hour NAAQS Nonattainment Area [87 FR 4812]
Feb. 7, 2021	Maintenance Plan for the Jackson County Nonattainment Area for the 2010 Sulfur Dioxide Standard
Feb. 7, 2021	Redesignation Request for the Jackson County Nonattainment Area Under the 2010 Sulfur Dioxide Standard
May 4, 2018	MoDNR Determination Request for Jackson County 2010 1-hour Sulfur Dioxide National Ambient Air Quality Standard Attainment	July 9, 2020	Air Plan Approval; Missouri and Kansas; Determination of Attainment for the Jackson County, Missouri 1-Hour Sulfur Dioxide Nonattainment Area and Redesignation of the Wyandotte County, Kansas Unclassifiable Area to Attainment/Unclassifiable [85 FR 41193]
Oct. 9, 2015	Nonattainment Area Plan for the 2010 1-Hour Sulfur Dioxide National Ambient Air Quality Standard: Jackson County Sulfur Dioxide Nonattainment Area (All elements withdrawn from EPA consideration except the base year emissions inventory) MoDNR Withdrawal Request-Nonattainment Area Plan for the 2010 1-Hour SO2 NAAQS: Jackson County MoDNR Withdrawal Request-10 CSR 10.6261 Control of Sulfur Dioxide Emissions Rule Action	Feb. 13, 2019	Air Plan Approval; Missouri; Emissions Inventory for the Missouri Jackson County and Jefferson County 2010 Sulfur Dioxide National Ambient Air Quality Standard Nonattainment Areas [84 FR 3703]

Round Two - Consent Decree

EPA designated no nonattainment areas in Missouri during this round.

Round Two - Boundary Recommendations Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
Sept. 2, 2020	Redesignation Request for the Labadie Unclassifiable Area Under the 2010 Sulfur Dioxide Standard	Aug. 6, 2020	EPA Response to Redesignation Request for Portions of Franklin and St. Charles Counties Under the 2010 Sulfur Dioxide Standard
April  19, 2016	MoDNR Response to EPA Proposed February 2016 Sulfur Dioxide Area Designation	July 12, 2016	Air Quality Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard-Round 2 [81 FR 45039] Effective: 9/12/2016
Sept. 24, 2015	2010 1-Hour Sulfur Dioxide Standard Area Boundary Recommendations, July 2016 Designation	Feb. 16, 2016	EPA Response to Recommendations on Air Quality Designations for 2010 National Ambient Air Quality Standard for Sulfur Dioxide - 120-day letter for round two designations Draft Technical Support Document: Missouri [Round 2] Area Designations for the 2010 SO2 Primary National Ambient Air Quality Standard

Round Three - Modeling

In August 2015, EPA finalized the data requirements rule, which details options for evaluating areas in rounds three and four of the 2010 SO₂ standard boundary designations. Round Three is for sources characterized by refined dispersion modeling of actual emissions. EPA designated no nonattainment areas in Missouri during this round.

Round 3 - Boundary Recommendations Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
May 3, 2018	Withdrawal of the Redesignation Request for the Sibley Generating Station	N/A	N/A
Oct. 23, 2017	MoDNR Response to EPA Proposed December 2017 Area Designations	Jan. 9, 2018	Air Quality Designations for the 2010 Sulfur Dioxide (SO2) Primary National Ambient Air Quality Standard—Round 3 [83 FR 1098]
Dec. 8, 2016	2010 1-Hour Sulfur Dioxide Standard Area Boundary Recommendations, December 2017 Designations	Aug. 22, 2017	EPA Response to Recommendations on Intended Designations for 2010 National Ambient Air Quality Standard for Sulfur Dioxide - 120-day letter for round three designations
July 2016	Modeling Protocol for Characterization of Air Quality, Federal Data Requirements Rule for the 2010 Sulfur Dioxide Standard, September 2016	N/A	NA
June 28, 2016	Evaluation Specifics for Sources Subject to the 2010 1-hour Sulfur Dioxide Data Requirements Rule	N/A	N/A
Jan. 15, 2016	List of Sources Subject to the 2010 1-Hour Sulfur Dioxide Data Requirements Rule	N/A	N/A

Round Four - Monitoring

Round Four is for sources characterized by newly installed SO₂ monitoring networks located in the areas of expected maximum concentration near high-emitting SO₂ sources. The EPA data requirements rule required Round Four monitors to begin operating by Jan. 1, 2017. State boundary recommendations were due by May 1, 2020, and EPA final boundary designations was due by Dec. 31, 2020. Three areas of Missouri have ambient SO₂ monitoring networks that were installed according to EPA’s data requirements rule. The Labadie, Missouri source had already been designated unclassifiable under the Round Two Designations, which may be considered for redesignation based on monitored SO₂ concentrations surrounding the facility.

Round Four - Monitoring Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
Oct. 16, 2020	Missouri Response to EPA 120-Day Letter on Round Four Designations Attachment 1 - AERMOD Model Performance Evaluation	March 26, 2021	Air Quality Designations for the 2010 Primary Sulfur Dioxide (SO2) National Ambient Air Quality Standard-Round 4 [86 FR 16055] Effective: April 20, 2021
April 30, 2020	Proposed Area Boundary Recommendations for the 2010 Sulfur Dioxide Standard: December 2020 Designations	Aug. 13, 2020	EPA Response to Recommendations on Intended Designations for Remaining Undesignated Areas for the 2010 1-hour National Ambient Air Quality Standard for Sulfur Dioxide Technical Support Document: Intended Round 4 Area Designations for the 2010 1-Hour SO2 Primary National Ambient Air Quality Standard

Round Four - Monitoring: Nonattainment Area Plans

EPA finalized designations for Round Four with an effective date of April 30, 2021. EPA designated a portion of New Madrid County as nonattainment in this round. This required the department to develop a nonattainment area plan for the area within 18 months.

New Madrid County Nonattainment Area Actions

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
May 3, 2023	New Madrid County Nonattainment Area Plan 2010 Sulfur Dioxide Standard Implementation Impact Report-Missouri State Implementation Plan: New Madrid Nonattainment Area Pursuant to the 2010 SO2 Standard	Pending	Pending
Nov. 3, 2021	New Madrid Nonattainment Area Plan for the 2010 Sulfur Dioxide Standard Presentation, Nov. 3, 2021

Annual Ongoing Data Requirements Report

For sources designated attainment according to the EPA SO₂data requirements rule based on modeling of actual emissions (generally Round Three sources), the federal rule requires the department to submit annual ongoing emissions evaluations from these sources to ensure emissions have not increased to a level that may cause a violation of the 2010 SO₂ standard.

• 2023 Annual Ongoing Data Requirements Report for Sulfur Dioxide
• 2022 Annual Ongoing Data Requirements Report for Sulfur Dioxide
• 2021 Annual Ongoing Data Requirements Report for Sulfur Dioxide
• 2020 Annual Ongoing Data Requirements Report for Sulfur Dioxide
• 2019 Annual Ongoing Data Requirements Report for Sulfur Dioxide
• 2018 Annual Ongoing Data Requirements Report for Sulfur Dioxide
• 2017 Annual Ongoing Data Requirements Report for Sulfur Dioxide 

Other SO2 SIPS

Other SO2 SIPS

MoDNR Submittal Date	MoDNR Action/Document	EPA Date	EPA Action/Document
Aug. 8, 2022	MoDNR Comment Letter on EPA Proposed Rule: Air Plan Disapproval of State Sulfur Dioxide Emissions	July 8, 2022	Air Plan Disapproval; Missouri; Control of Sulfur Dioxide Emissions [87 FR FR 40759]
April 14, 2022	Ameren Sioux Sulfur Dioxide Consent Agreement	Pending	Pending
Feb. 17, 2022	Evergy - Lake Road Sulfur Dioxide Consent Agreement - 2021 Revision	Pending	Pending