Air Pollution from Sulfur Dioxide
- What is sulfur dioxide?
- National Ambient Air Quality Standards (NAAQS) for SO2
- Latest Air Quality Planning Activities
- Get more information or contact the TCEQ
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 also 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 of high-sulfur fuels in locomotives, large ships, and non-road equipment.
National Ambient Air Quality Standards (NAAQS) for SO2
The United States Environmental Protection Agency (EPA) issued annual and 24-hour primary, or 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 In 1973, the secondary annual SO2 standard was revoked, and the secondary three-hour standard was retained.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.
The EPA strengthened the SO2 NAAQS on June 2, 2010, with a new 75 parts per billion (ppb) one-hour primary standard (75 FR 35520). 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. The 2010 SO2 one-hour primary standard became effective August 23, 2010.
In the rulemaking for the 2010 standard, the EPA revoked the existing SO2 annual and 24-hour primary standards for areas not previously designated nonattainment for SO2, effective one year after designations for the 2010 standard. 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.
Texas Compliance with the SO2 NAAQS
Texas currently has no areas designated nonattainment for any SO2 air quality standard. A February 7, 2013 letter from the EPA conveyed that no areas of Texas will be initially designated nonattainment for the 2010 SO2 standard, based on the EPA's review of 2009 through 2011 air quality data showing no violations of the standard.
Implementation of the 2010 SO2 Primary NAAQS
Texas submitted its recommended designations to the EPA on June 2, 2011. Texas subsequently revised its recommendation pertaining to Jefferson County on April 20, 2012. Texas' final recommended designations were: attainment for Dallas, Ellis, El Paso, Galveston, Gregg, Harris, Jefferson, Kaufman, McLennan, and Nueces Counties; and unclassifiable for all remaining counties. The recommendations were based on the 2011 design values for existing SO2 regulatory monitors.
A February 7, 2013 letter from the EPA indicated that no areas in Texas will be designated nonattainment in the EPA's initial round of designations, based on its review of 2009 through 2011 air quality data showing no violations of the standard in Texas. The EPA's letter stated that designation action for Texas is deferred until additional data are gathered. The EPA expects to proceed with designation action in Texas once data are gathered pursuant to its comprehensive implementation strategy.
The EPA has delayed completing area designations under the 2010 SO2 primary standard for all areas except those determined to be in nonattainment based on ambient air quality monitoring data indicating violation(s) of the standard. The EPA intends to finalize only nonattainment area designations by June 3, 2013, and will address the designations for all other areas in separate future actions. The EPA now 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.
Initial implementation instructions for the 2010 SO2 NAAQS conveyed the EPA’s expectation for infrastructure SIP submittals to include maintenance plans with modeling demonstrations for areas designated unclassifiable. A requirement for the use of American Meteorological Society/Environmental Protection Agency Regulatory Model (AERMOD) refined dispersion modeling to assess compliance by large SO2 sources was also discussed in the rule. The maintenance plan and modeling demonstration expectations led to challenges by Texas and others to the standard. Texas’ Petition for Review was denied by the United States Court of Appeals for the D.C. Circuit on July 20, 2012. On January 24, 2013 the D.C. Circuit denied the petitions for rehearing and rehearing en banc, and on February 4, 2013 the court issued the mandate in the case.
Other requirements of the 2010 SO2 NAAQS include fully operational SO2 air quality monitors in place by January 1, 2013 based on recent census and emissions data. Seven monitors are required in Texas. Two monitors are required 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.
In September 2011, the EPA issued draft guidance , but it was not finalized. An April 12, 2012, letter to states and tribes from the EPA provided updated expectations for infrastructure and transport SIP revisions for the 2010 SO2 NAAQS. The letter conveyed that the EPA has now put maintenance plan and modeled demonstration requirements for infrastructure SIPs for the 2010 SO2 standard on hold pending further evaluation. In spring 2012, the EPA conducted stakeholder outreach to discuss the issues associated with implementing the 2010 SO2 standard.
Updated EPA Strategy
In February 2013, the EPA updated its strategy for completing initial area designations under the 2010 SO2 NAAQS, and notified states on February 6, 2013 via a conference call. The EPA intends to meet the June 2013 designations deadline only for areas determined to be in nonattainment of the 2010 SO2 NAAQS, based on air monitoring data from 2009 through 2011 indicating violations of the standard.
The EPA now 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 a mix of 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 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.
Latest Air Quality Planning Activities
Last updated: 4/23/2013
Infrastructure and Transport SIP Revision for the 2010 SO2 NAAQS
On, 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.
A public hearing on the proposed SIP revision was offered on December 4, 2012 at TCEQ Headquarters in Austin, but there were no public attendees. The public comment period closed on December 7, 2012. Comments were received from the Sierra Club and the EPA. The comments were addressed in the Response to Comments section of the SIP revision.
- SIP Revision
In January 2011, the TCEQ hosted meetings in Austin and Port Arthur to present information on the 2010 SO2 NAAQS and area designation requirements for Texas.
Get more information or contact the TCEQ
Related Web pages and publications
- EPA General Page on Sulfur Dioxide
- EPA Primary NAAQS for Sulfur Dioxide
- EPA Secondary NAAQS for Sulfur Dioxide
- Texas SIP Revisions
Contact the TCEQ