Sulfur dioxide (SO2) is a colorless gas with a strong, suffocating odor. Sources of sulfur dioxide emissions include fossil-fuel fired power plants, metal/ore processing industries, other industries that combust fossil fuels, and certain nonroad engines such as locomotives and marine vessels. Exposure to elevated concentrations of sulfur dioxide can cause irritation of the throat and lungs, leading to difficulty breathing, increased asthma symptoms and other respiratory illnesses. The department monitors sulfur dioxide levels in the air at locations across the state.

Sulfur dioxide is one of the Environmental Protection Agency's criteria air pollutants – commonly found air pollutants that can harm people and the environment at high enough levels. Because of the potential to harm people and the environment, the federal Clean Air Act and Missouri Air Conservation Law limit the amount of sulfur dioxide that sources can emit into the atmosphere. Sulfur dioxide also contributes to the formation of secondary fine particle pollution, which is a subset of particulate matter, another criteria pollutant.

Sulfur Dioxide National Ambient Air Quality Standard (NAAQS)

In June 2010, the EPA established a new 1-hour primary sulfur dioxide standard of 75 parts-per-billion. The previous sulfur dioxide primary standards set in 1971 included a 24-hour standard at 140 parts-per-billion and annual standard at 30 parts-per-billion. There is also a secondary sulfur dioxide standard based on a 3-hour average set at 500 parts per billion. When the EPA revised the sulfur dioxide standard in 2010, they revoked the two previous primary standards, replacing them with the new 1-hour primary standard and they retained the existing secondary standard.

2010 1-hr SO2 Primary Standard: 75 ppb

When the EPA revises a National Ambient Air Quality Standard, states are allowed to submit boundary designation recommendations to the EPA for consideration when establishing the final boundary designations. For most criteria pollutants, states are given one year to submit their recommendations and the EPA finalizes boundary designations within two years.

The EPA has chosen a different approach to establish boundary designations under the 2010 sulfur dioxide standard. Unlike other criteria pollutants, sulfur dioxide is almost exclusively a point source-emitted pollutant. Additionally, transport of sulfur dioxide emissions is typically more localized and is less likely to be observed on a regional scale. A monitoring network large enough to adequately cover all large sources would be prohibitively expensive and an affordable network would leave large gaps in coverage. Therefore, the EPA has decided to use a hybrid monitoring-modeling approach for sulfur dioxide. Additionally, the EPA is splitting the boundary designation process into multiple rounds. The initial round for boundary designations was based on available ambient air quality monitoring data. Additional rounds of designations are based on a hybrid approach involving emissions inventory analysis, an enhanced monitoring network and extensive use of refined air dispersion modeling.

As the state develops new boundary designation recommendations and state implementation plans, they will be made available for public review and comment online at http://dnr.mo.gov/env/apcp/stateplanrevisions.htm.

 

Infrastructure plan: 2010 SO2 standard

After the EPA finalizes a new standard, states have three years to develop an infrastructure plan that demonstrates the state’s ability to implement, maintain and enforce the standard.

Date EPA Approval Document
MACC Adoption:
June 2013
Pending Section 110 Infrastructure SIP for the 2010 SO2 NAAQS

Initial round: Plans for nonattainment area — Jefferson County (part), St. Louis

According to data from ambient air monitors between 2007 - 2009 and 2010 - 2012, areas in Jackson County and Jefferson County were in violation of the 2010 one-hour SO2 standard. Based on these violations, the EPA designated part of Jefferson County as nonattainment under the 2010 standard, effective in October 2013.

Jefferson County Area in St. Louis Region

Date EPA Approval Document
MACC Adoption:
May 2015
Pending

Jefferson County SO2 Nonattainment Area Plan
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Appendix H
Appendix I
Appendix J

The modeling performed in support of the Jefferson County Nonattainment Plan takes into account federally enforceable SO2 emission reductions from the closure of the Doe Run Herculaneum primary lead smelter. The closure of the smelter was required by the consent decree between Doe Run, the department and the EPA filed in the U.S. District Court in the Eastern District of Missouri, Case No. 4:10-cv-01895-JCH, and entered on Dec. 21, 2011. For more information, go to epa.gov/region7/cleanup/doe_run/pdf/consent_decree.pdf

Feb. 2, 2016  

According to monitoring data from 2013-2015, the Jefferson County nonattainment area has attained the standard. For more information, see the department's SO2 monitoring webpage .

Clean Data Determination Request letter to EPA

TBD   Redesignation Request and Maintenance Plan

Initial round: Plans for nonattainment area — Jackson County (part), Kansas City

According to data from ambient air monitors between 2007 - 2009 and 2010 - 2012, areas in Jackson County and Jefferson County were in violation of the 2010 one-hour SO2 standard. Based on these violations, the EPA designated part of Jackson County as nonattainment under the 2010 standard, effective in October 2013.

Jackson County Area in Kansas City Region

Date EPA Approval Document
MACC Adoption:
May 2015
Pending

Jackson County SO2 Nonattainment Area Plan
Appendix A
Appendix B 
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Appendix H
Appendix I
Appendix J

TBD  

The Jackson County nonattainment area is expected to attain the standard by the attainment date of October 2018. For more information, see the department's SO2 monitoring data webpage .

TBD   Redesignation Request and Maintenance Plan

Round 2 -- Consent Decree Round

To resolve litigation surrounding the process for designating SO2 boundaries, the EPA signed on March 2, 2015, a consent decree with the Sierra Club and Natural Resources Defense Council. The decree imposes a strategy and timeline for future rounds of designating SO2 boundaries. More information. ...

Date
Action
Sept. 24, 2015

Sulfur Dioxide Boundary Recommendations for July 2016 Designations

February 2016

EPA 120-Day Letter

Attachment to EPA 120-Day Letter

April 2016

Response to EPA 120-Day Letter

Attachment 1

Attachment 2

Attachment 3

July 12, 2016 Federal Register Notice for the July 2016 Round of SO2 Boundary Designations

Round 2 (Consent Decree Round): Nonattainment area plans

EPA designated no nonattainment areas in Missouri during this round.

Round 3 -- Modeling

In August 2015, the EPA finalized the data requirements rule, which details options for evaluating areas in two additional rounds of SO2 boundary designations and other requirements as applicable. Round 3 is for sources characterized by modeling. Round 4 is for sources characterized by approved monitoring networks required to commence data collection by January 1, 2017, in addition to modeling requirements to establish such networks.

 

Completion Date/
Expected Date

Action Related to Round 3 of the Boundary Designation Process for the 2010 SO2 Standard

January
2016

State-submitted list of SO2 sources that emitted more than 2,000 tons per year (tpy) of SO2 in 2014 and that will be evaluated under the EPA's data requirements rule

July
2016

State-submitted details of how each SO2 source identified in January 2016 will be characterized. Options: a new limit, modeling or new air quality monitors

July
2016

Modeling protocol submitted to the EPA for sources characterized by modeling

January
2017

State-submitted modeling analyses and boundary recommendations for sources characterized by modeling

2010 SO2 Recommendations for December 2017 Designations

January
2017

Effective date for compliance with the data requirements rule for sources characterized by modeling

August
2017

EPA to notify states of intended designations for sources characterized by modeling via 120-day letters

December
2017

Final designations for sources characterized by modeling

Round 3 (Modeling): Nonattainment area plans per 2010 SO2 standard

The EPA will finalize designations for this round by December 2017.  If new areas in Missouri are designated nonattainment for the 2010 sulfur dioxide standard in round 3, then nonattainment-related SIP elements are also required for those areas.

Expected Date

Action

August 
2019

States to submit nonattainment-related plans for areas designated nonattainment based on modeling characterization


Round 4 -- Monitoring

Completion Date/ Expected Date

Action

January
2017

SO2 monitors that satisfy the data requirements rule must be operational. Per data requirements rule,this link includes source specific sites that began monitoring on January 1, 2017 or March 22, 2015.

May
2020

Certified monitoring data submitted for 2017 – 2019
States to submit recommendations for sources characterized by monitoring

August
2020

EPA to notify states of intended designations for sources characterized by monitoring via 120-day letters

December
2020

Final designations for sources characterized by monitoring

Round 4 (Monitoring): Nonattainment area plans

The EPA will finalize designations for the round by December 2020. If the EPA designates new areas in Missouri as nonattainment for the 2010 SO2 standard in round 4, then additional nonattainment-related SIP elements are also required for those areas.

Expected Date

Action

August
2022

States to submit nonattainment-related SIPs for areas designated nonattainment based on 2017 - 2019 monitoring data from new SO2 monitors