Air Pollution Control Program

Sulfur Dioxide

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Information icon Recent Announcement

On April 12, 2012, EPA sent a letter to all states outlining the next steps with regard to implementation of the 1-hour sulfur dioxide (SO2) standard.  The letter sent to Missouri is available on the Web. We understand all letters sent to states are the same.

As detailed in the letter, EPA plans to: 

  1. Move forward with the current nonattainment designations process as soon as possible.
  2. Initiate stakeholder outreach in the near future to ask for input on monitoring, modeling, and implementation issues, particularly for unclassifiable areas.
  3. No longer require refined modeling demonstrations content for the June 2013 Infrastructure SIP submittal required for unclassifiable areas.  However, a traditional Infrastructure SIP must still be submitted in June 2013. 

The information contained in this letter impacts the next steps the Air Program will take regarding implementation of the 1-hour SO2 standard.  We are still working to determine what these next steps will be and will post additional information as it becomes available.

Sulfur Dioxide

Sulfur dioxide is a colorless gas with a strong, suffocating odor. It can cause irritation of the throat and lungs, leading to difficulty breathing, increased asthma symptoms and more respiratory illnesses.

Sulfur dioxide is sometimes referred to as one of the Environmental Protection Agency's criteria air pollutants. Criteria pollutants are commonly found air pollutants that, at high enough levels, can harm human health and the environment. Because of the potential to harm people and the environment, EPA and the Department of Natural Resources limit the amount of sulfur dioxide sources can emit into the atmosphere. The department monitors sulfur dioxide levels in the air at certain locations across the state. Sulfur dioxide also contributes to the formation of fine particle pollution, another criteria pollutant, also known as particulate matter.

Sulfur Dioxide - National Ambient Air Quality Standard Revision

Map of sulfur dioxide monitoring sites around the state.In June 2010, EPA established a new 1-hour primary sulfur dioxide standard of 75 parts-per-billion. States must submit boundary recommendations for area designations using this new standard to EPA by June 2011, and EPA expects to issue final designations by June 2012. EPA anticipates initially designating areas based on 2008 to 2010 monitoring data or refined dispersion modeling results if provided by the state. Areas violating the standard based on monitoring or modeling data would be designated as nonattainment and all other areas would be designated either attainment or unclassifiable.

EPA plans to issue guidance on the use of air quality models to support designations, state implementation plan development and other implementation issues related to the new sulfur dioxide standard. EPA expects to finalize this guidance in summer 2011. As the sulfur dioxide modeling and implementation guidance is finalized, the department intends to conduct refined dispersion modeling of sulfur dioxide sources in accordance with EPA’s guidelines and provide additional technical justification as needed for the recommended nonattainment area boundaries.

Based on current data, monitors located in Kansas City, Herculaneum and Springfield are in violation of the 1-hour sulfur dioxide standard. Based on violations recorded at these monitors, the Air Program is required to recommend a nonattainment area boundary for each of these three areas.

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Boundary Designation Process

EPA requires each state to determine which areas in the state will not meet the 2010 National Ambient Air Quality Standard for sulfur dioxide, known as nonattainment areas. Since the 2010 sulfur dioxide standard does not require modeling for initial nonattainment determinations and EPA’s modeling guidance was not available in time to accommodate our public hearing deadlines, the department is basing boundary recommendations on factors other than modeling, such as monitoring data, emissions data, and meteorology. The department intends to present draft nonattainment recommendations at public information sessions held in areas with violating monitors during early April 2011 and at the formal public hearing on April 28. The department intends to submit the nonattainment boundary designation to EPA by the June 2, 2011 deadline. EPA has one year to approve or modify the designation and has the authority to make the final determination of nonattainment area boundaries.

The EPA has chosen a different approach to determine attainment status for 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 dependent 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, EPA has decided to use a hybrid monitoring-modeling approach for sulfur dioxide. This hybrid approach involves a modest monitoring network and extensive use of refined air dispersion modeling. A combination of monitoring and modeling will also be used to assess compliance with the 2010 1-hour sulfur dioxide standard.

A summary of the implementation timeline for the 1-hour sulfur dioxide standard is as follows:

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Meetings

To help communities that may be designated as nonattainment, the department has and will be holding public meetings with local city, county and business leaders. Documents and presentations from these meetings will be posted here.

Festus

Kansas City

Springfield

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Links

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