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Sulfur Dioxide

Sulfur Dioxide Implementation - Programs and Requirements for Reducing Sulfur Dioxide

The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for six criteria pollutants; sulfur dioxide is one of these.  EPA works with partners at state, local, and tribal air quality agencies to meet these standards.

EPA issued the final primary NAAQS for SO2 on June 2, 2010.   EPA will “designate” areas for the standard by June 2012, two years following the promulgation of the standard. Designations for the revised standard would rely upon the monitors currently in place that evaluate area-wide concentrations of SO2 as well as available modeling data indicating a violation of the standard.  State Implementation Plans designed to reduce emissions in areas designated as nonattainment will be due within 18 months of the effective date of designation, and the attainment date for nonattainment areas will be within 5 years of designation.

Under the Clean Air Act (CAA), as amended in 1990, each state must develop a plan describing how it will attain and maintain the NAAQS.  In other words, how it plans to clean up polluted areas and keep them clean.  This plan is called the State Implementation Plan (SIP) and is required under Section 110 of the CAA (40 CFR Part 51, Subparts F & G).  In general, the SIP is a collection of programs, including:

  • a monitoring program, which is a collection of monitoring devices throughout the country which provide actual measurements of the concentrations in the air, to identify whether an area is meeting the air quality standards, and if not, how much reductions are needed to meet those standards;
  • air quality calculations and computer modeling, which are used to predict future trends and the effects of emissions reduction strategies;
  • emissions inventories, which describe the sources and categories of emissions to the air for a given pollutant, and how much is emitted by each source or source category;
  • control strategy studies whose goal is finding the best way to reduce emissions in order to meet air quality standards;
  • formal adoption of measures (enforceable by EPA, States and citizens) which ensure that we will achieve the reductions deemed necessary in the planning process;
  • periodic review to evaluate whether those needed reductions were achieved in reality, and whether they had the predicted result.

The air quality agency responsible for the State Implementation Plan, (usually a state agency) must provide the public an opportunity to review the plan before sending it to EPA for approval.

In cases where the EPA fails to approve a state implementation plan, the Agency can issue and enforce a Federal Implementation Plan (FIP) to ensure attainment and maintenance of the NAAQS.   In addition, the Clean Air Act contains penalties, referred to as "sanctions" which EPA can impose in areas not satisfying the State Implementation Plan requirements. 

Stakeholder Outreach

EPA is seeking additional input from states, tribes, and other interested parties to refine the agency's approach for implementing the SO2 standard. We have set up an outreach process that allows for focused discussion of monitoring, modeling and implementation issues. This effort will ensure that the agency has the information it needs to protect public health from unhealthy levels of SO2 in the outdoor air.

EPA provided letters to states and tribes to notify them of these plans. Samples of the state and tribal letters are included below. These letters do not represent final agency action.

EPA is convening three small group meetings with stakeholders to discuss issues associated with implementation of the SO2 standard.

Schedule for Stakeholder Discussions

  • Session 1: Environmental and Public Health Organization Representatives
    May 30, 2012, Washington, DC
  • Session 2: State and Tribal Representatives
    May 31, 2012, Research Triangle Park, NC
  • Session 3: Industry Representatives
    June 1, 2012, Research Triangle Park, NC

For more information about these meetings, please contact Carolyn Childers at (919) 541-5604.

White Paper

To stimulate discussion at the small group meetings and to promote progress toward a workable approach for implementing the 1-hour SO2 standard, EPA developed a white paper that identifies important questions about how we could determine whether an area is meeting the SO2 standard and how we might use monitoring, modeling, or a combination of monitoring and modeling. The current version of the white paper is included below, along with summary information for the stakeholder discussions. This white paper is not a final agency action.

Other Opportunities to Comment

In addition to the opportunity to comment on the white paper at the small group meetings, EPA will also be accepting written comments on topics covered in the white paper. Comments will be accepted through Friday, June 29, 2012. This is a 1-week extension from the date originally announced.

You may submit comments, identified by Docket ID No. EPA-HQ-OAR-2010-1059, by one of the following methods:

  • http://www.regulations.gov. Follow the on-line instructions for submitting comments.
  • Email: a-and-r-docket@epa.gov. Attention Docket ID No. EPA-HQ-OAR2010-1059.
  • Fax: 202-566-9744. Attention Docket ID No. EPA-HQ-OAR-2010-1059.
  • Mail: Air Docket, Attention Docket ID No. EPA-HQ-OAR-2010-1059, Environmental Protection Agency, Mail Code: 6102T, 1200 Pennsylvania Ave., NW, Washington, D.C. 20460.

Summary of Key Comments

High level summaries of key comments from the stakeholder meetings are provided below.

Draft Implementation Guidance for the Primary National Ambient Air Quality Standard for Sulfur Dioxide


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