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Air Pollution from Sulfur Dioxide

General information on sulfur dioxide and air quality standards, Texas' compliance status, and latest air quality planning activities.

What is sulfur dioxide?

Sulfur dioxide (SO2) is one of a group of highly reactive gases called sulfur oxides (SOX). Exposure to SO2 can affect the respiratory system, especially for people with asthma. Studies show connections between short-term exposure and increased visits to emergency departments and hospital admissions for respiratory illnesses, particularly in populations at risk (including children, the elderly, and asthmatics). SOX can react with other compounds in the atmosphere to form small particles that cause or worsen respiratory disease or aggravate existing heart disease.

The largest source of SO2 emissions is fossil fuel combustion at power plants and other industrial facilities. SO2 emissions also come from extraction of metal from ore and burning high-sulfur fuels in locomotives, large ships, and non-road equipment.

National Ambient Air Quality Standards (NAAQS) for SO2

History of the SO2 NAAQS

The United States Environmental Protection Agency (EPA) issued annual and 24-hour primary (health-based) SO2 standards as well as three-hour and annual secondary SO2 standards in 1971. In 1973, the secondary annual SO2 standard was revoked, and the secondary three-hour standard was retained. In 1996, the EPA retained both the annual and 24-hour primary SO2 standards.

Effective August 23, 2010, the EPA strengthened the SO2 NAAQS with a new primary one-hour standard of 75 parts per billion (ppb) (75 FR 35520).Exit the TCEQ A one-hour standard was determined to better protect the public from exposure to high short-term SO2 concentrations, especially in communities located close to coal-fired power plants, industrial boilers, petroleum refineries, metal processing plants, and diesel exhausts.

In setting the 2010 primary one-hour SO2 standard, the EPA revoked the annual and 24-hour primary standards for areas not previously designated nonattainment, to become effective one year after designations for the 2010 standard are finalized. In areas previously designated nonattainment for SO2 under the 1971 standards, the annual and 24-hour standards remain in effect until implementation plans to attain or maintain the 2010 standard are approved by the EPA.

Texas Compliance with the SO2 NAAQS

Texas currently has no areas designated nonattainment for any SO2 air quality standard.

Implementation of the 2010 Primary SO2 NAAQS

Texas recommended to the EPA that Dallas, Ellis, El Paso, Galveston, Gregg, Harris, Jefferson, Kaufman, McLennan, and Nueces Counties be designated attainment for the 2010 SO2 standard; and all remaining counties be designated unclassifiable. Texas' recommendation was based on 2011 design values for existing SO2 regulatory monitors.

On August 5, 2013, the EPA published final nonattainment area designations for areas with 2009 through 2011 monitoring data indicating violations of the one-hour SO2 standard (78 FR 47191) Exit the TCEQ. There are no nonattainment areas in Texas. Final designations for areas not identified in 2013 as nonattainment are anticipated by December 2017 for modeled areas, and December 2020 for monitored areas. Additional information on the EPA's still developing SO2 implementation strategy can be found at the EPA's Sulfur Dioxide Implementation Web page. Exit the TCEQ

The 2010 SO2 NAAQS requires two monitors in the Houston-Sugar Land-Baytown area, and one monitor is required in each of the following areas: San Antonio-New Braunfels, Dallas-Fort Worth-Arlington, Longview, Beaumont-Port Arthur, and Amarillo. Currently, the TCEQ and local agencies monitor actual concentrations of SO2 at 27 sites across Texas.

The EPA intends to provide flexibility for air agencies to determine the most appropriate and effective approach for characterizing air quality in their jurisdictions – through monitoring, modeling, or both. The EPA intends to allow a workable time frame for agencies to monitor air quality near key sources (or alternatively to characterize air quality through modeling). The EPA’s updated strategy paper Exit the TCEQ issued in February 2013 indicates that final designations for the areas not identified in 2013 as nonattainment will not be made until December 2017 for modeled areas, and December 2020 for monitored areas. For more information, please visit the EPA's Sulfur Dioxide Implementation Web page. Exit the TCEQ

Latest Air Quality Planning Activities

Last updated: 4/23/2013

Infrastructure and Transport SIP Revision for the 2010 SO2 NAAQS

On April 23, 2013, the commission adopted the Federal Clean Air Act (FCAA), §110(a)(1) and (2) Infrastructure and Transport SIP Revision for the 2010 SO2 NAAQS (Project No. 2012-022-SIP-NR).

The SIP revision identifies basic program elements enabling Texas to meet infrastructure requirements for the 2010 SO2 NAAQS, as stipulated in the FCAA. The revision specifically addresses FCAA, §110(a)(2)(D)(i)(I) transport requirements with a technical demonstration showing Texas does not contribute significantly to nonattainment nor interfere with maintenance of the SO2 NAAQS in any other state.

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Related Web pages and publications

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