An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Sulfur Dioxide (SO2) Pollution

Specific Elements for Each of the Major SIP Types for Sulfur Dioxide (SO2)

Infrastructure State Implementation Plan (SIP)

An infrastructure SIP, or i-SIP, is a requirement for all states, regardless of designation. Even areas in attainment must demonstrate what controls they will continue to use and regulate in order to remain in attainment.

Nonattainment New Source Review SIP

Nonattainment Area SIP

  • If an area is designated as nonattainment, the state must develop an additional SIP detailing the path to attainment. The SIP will require different elements depending on how far the area is from being able to reach attainment.

Interstate transport SIP

Redesignation SIP, or maintenance SIP