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Sulfur Dioxide Designations

Learn About Sulfur Dioxide Designations

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Designations Basics

What does designation mean?

States and tribes submit recommendations to EPA as to whether or not an area is attaining the national ambient air quality standards for a criteria pollutant. The states and tribes base these recommendations on air quality data collected from monitors at locations in urban and rural settings. After working with the states and tribes and considering the information from air quality monitors, EPA will then "designate" an area as attainment or nonattainment for the sulfur dioxide (SO2) standard. If an area is designated as nonattainment, it signifies that the air in the area is unhealthy to breathe.

What does nonattainment mean?

The Clean Air Act identifies six common air pollutants that are found all over the United States. These pollutants can injure health, harm the environment and cause property damage. EPA calls these pollutants criteria air pollutants because the agency has developed health-based criteria (science-based guidelines) as the basis for setting permissible levels in the air we breathe. Sulfur dioxide is a criteria pollutant. EPA establishes national ambient air quality standards for each of the criteria pollutants. These standards apply to the concentration of a pollutant in outdoor air. If the air quality in a geographic area meets or is cleaner than the national standard, it is called an attainment area; areas that don't meet the national standard are called nonattainment areas. In order to improve air quality in a nonattainment area, states must draft a plan known as a state implementation plan (SIP). The plan outlines the measures that the state will take in order to improve air quality. Once a nonattainment area meets the standards and additional redesignation requirements in the Clean Air Act [Section 107(d)(3)(E)], EPA will designate the area to attainment.

What will my area need to do to improve air quality if it is designated nonattainment for SO2?

States with designated nonattainment areas are required under the Clean Air Act to develop a State Implementation Plan and submit it to EPA within 18 months. (Tribes may elect to develop tribal implementation plans but are not required to do so.) This plan must include enforceable measures for reducing air pollutant emissions. The plan must also provide steps for the area to attain the SO2 standards as quickly as possible, and the area must show how it will make reasonable progress toward attaining the standards. In assessing how quickly an area can attain the standards, states should consider the air quality improvements that can be achieved from a combination of national, state, and local measures. For example, states should take into account existing emission reduction programs, plus any new programs or regulations that can be implemented within the state or local nonattainment area.

Status and Next Steps

On July 25, 2013, EPA identified or “designated” 29 areas in 16 states as “nonattainment” for the 2010 SO2 standard. Air quality monitors in each of these areas measured violations of the standard based on 2009 – 2011 data. State plans demonstrating how these areas will meet the SO2 standard were due to EPA by April 4, 2015.

On March 2, 2015, the U.S. District Court for the Northern District of California accepted, as an enforceable order, an agreement between EPA and Sierra Club and Natural Resources Defense Council to resolve litigation concerning the deadline for completing the designations. The court’s order directs EPA to complete designations for all remaining areas in the country in up to three additional rounds: the first round by July 2, 2016, the second round by December 31, 2017, and the final round by December 31, 2020.