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 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. As a result of the EPA's review of the SO2 NAAQS in 1973, the secondary annual SO2 standard was revoked and the secondary three-hour standard was retained. Following a subsequent review of the NAAQS in 1996, the EPA retained both the annual and 24-hour primary SO2 standards.
2010 SO2 NAAQS Revision
Effective August 23, 2010, the EPA revised the SO2 NAAQS, adding a primary one-hour standard of 75 parts per billion (ppb) (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.
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. For areas of the country previously designated nonattainment for SO2 under the 1971 standards, the annual and 24-hour standards remain in effect until state implementation plans to attain or maintain the 2010 standard are approved by the EPA.
Implementation of the 2010 Primary SO2 NAAQS
Round One Designations
In June 2011, Texas recommended to the EPA that Jefferson County be designated as nonattainment for the 2010 SO2 standard; that Dallas, Ellis, El Paso, Galveston, Gregg, Harris, Kaufman, McLennan, and Nueces Counties be designated attainment; and all remaining counties be designated unclassifiable. Texas' recommendation was based on 2009 and preliminary 2010 design values for the state's existing SO2 regulatory monitors.
In April 2012, Texas submitted a revised recommendation 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' revised recommendation was based on 2011 design values for the state's 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). No areas of Texas were designated.
Round Two Designations
A consent decree to resolve EPA’s failure to timely promulgate designations was ordered by the U.S. District Court for the Northern District of California on March 3, 2015. The court-ordered settlement established deadlines for the EPA to complete designations in several rounds. Areas with newly monitored violations or large emissions sources not announced for retirement as of March 2015, with 2012 SO2 emissions greater than 16,000 tons per year (tpy) or greater than 2,600 tpy with average emission rate greater than 0.45 pounds per million British thermal units (lbs/MMBtu), were to be designated by the EPA in round two by July 2, 2016.
In a letter dated March 20, 2015, the EPA identified 12 electric power plants in Texas with emissions meeting the court-ordered consent decree criteria for designation by July 2016. No monitors with violations of the 2010 primary SO2 NAAQS were identified in Texas. The EPA’s letter provided Texas with an opportunity to revise previously recommended designations, and to submit supporting data and any additional information for EPA consideration, by September 18, 2015. (see the Latest Air Quality Planning Activities section for Texas' September 18, 2015 revised recommendation). Following the state's revised recommendation, the EPA issued a 120-day notice to Texas on February 11, 2016 with proposed designations for counties surrounding the 12 facilities. The state’s response to the EPA’s 120-day notice was submitted to the EPA on April 19, 2016. On June 30, 2016, the EPA notified the governor that it is designating Atascosa, Fort Bend, Goliad, Lamb, Limestone, McLennan, and Robertson Counties as unclassifiable/attainment and Potter County as unclassifiable. Designations were published in the Federal Register on July 12, 2016 with an effective date of September 12, 2016 (81 FR 45039). Designations for Freestone, Anderson, Milam, Rusk, Gregg, Panola, and Titus counties have been delayed. Counties designated unclassifiable in round two will be addressed under the EPA’s Data Requirements Rule for designation in rounds three or four.
For more information visit the EPA’s SO2 Designations - Round 2 State Recommendations and EPA Responses Web page.
Rounds Three and Four Designations and the Data Requirements Rule
The EPA’s Data Requirements Rule (DRR) for the 2010 primary one-hour SO2 NAAQS, finalized on August 10, 2015 and published on August 21, 2015 (80 FR 51052), provides three options for states to characterize and assess SO2 air quality near sources that emit greater than 2,000 tpy: (a) modeling, (b) monitoring, or (c) enforceable emissions limits (below 2,000 tpy). Areas to be characterized by modeling and other areas without monitors will be designated by the EPA in round three by December 31, 2017. Areas to be characterized by monitoring as well as any remaining undesignated areas will be designated by the EPA in round four by December 31, 2020.
The DRR requires states to identify and submit a list to EPA of all applicable emissions sources by January 15, 2016. The TCEQ identified 25 sources in Texas with emissions greater than 2,000 tpy, and notified the EPA on January 15, 2016. On April 22, 2016, the TCEQ requested revision of the list down to 24 sources, and the EPA concurred on May 4, 2016. By July 1, 2016, Texas was required to identify the characterization approach planned for each identified source. For any source to be evaluated with modeling, states must submit a modeling protocol by July 1, 2016, a modeling analysis by January 13, 2017, and annual reports thereafter, to the EPA. For sources to be monitored, the SO2 monitors must be operating by January 1, 2017. Any enforceable emissions limits agreed to must be adopted and effective by January 13, 2017. On June 29, 2016, the TCEQ submitted an air quality characterization plan and modeling protocol for identified sources.
For more information, please visit the EPA's SO2 Data Requirements Rule Web page.
For a complete timeline of the EPA's designation process, including submittal deadlines per the DRR, see the Timeline for the 2010 SO2 NAAQS Designations Process.
Last updated: 7/29/2016
Air Quality Characterization Plan for Areas with Identified SO2 Sources
The Data Requirements Rule requires air agencies to notify the EPA by July 1, 2016 of the air quality characterization method planned to evaluate areas where identified sources are located. Air agencies were also required to submit revised monitoring network plans and modeling protocols to the EPA by July 1, 2016 to address sources to be evaluated through monitoring and modeling. On June 29, 2016, the TCEQ submitted an air quality characterization plan to evaluate each of the areas where 24 sources were identified in Texas. The plan included reference to the TCEQ's 2016 Air Monitoring Network Plan (submitted separately) and an attached modeling protocol for the Oklaunion Power Station.
- Air Quality Characterization Plan
- 2016 Air Monitoring Network Plan (See Appendix E: Sulfur Dioxide Data Requirements Rule Monitor Placement Evaluations)
- Air Quality Modeling Protocol for the Oklaunion Power Station
SO2 Sources Identified for Further Evaluation Per the Data Requirements Rule
The TCEQ identified 25 sources in Texas with emissions greater than 2,000 tpy, and notified the EPA on January 15, 2016. On April 22, 2016, the TCEQ requested revision of the list down to 24 sources, and the EPA concurred on May 4, 2016.
- January 15, 2016 List of Identified SO2 Sources
- April 22, 2016 Request to Revise List of Sources
- May 4, 2016 EPA Concurrence Letter
Revised Designation Recommendations for the 2010 Primary SO2 NAAQS
On September 18, 2015, Texas submitted revised designation recommendations and supporting information to the EPA to address 12 facilities in Texas with SO2 emissions meeting the court-ordered consent decree criteria for designation by July 2, 2016. Texas recommends attainment designations for Dallas, El Paso, Ellis, Galveston, Gregg, Harris, Jefferson, Kaufman, McLennan, Navarro, and Nueces Counties. These 11 counties have certified air monitoring data showing compliance with the 2010 SO2 NAAQS. Texas recommends unclassifiable/attainment designations for the remainder of the state (243 counties).
- Revised Recommendation Letter
- Attachment A: Recommended Designations for the 2010 One-Hour SO2 NAAQS
- Attachment B: TCEQ Analyses
- Attachment C: Evaluation of the Impact of Sandy Creek Energy Station SO2 Emissions
- Attachment D: Information Submitted to the TCEQ for the Coleto Creek Power Station
- Attachment E: Information Submitted to the TCEQ for the San Miguel Electric Plant
- Attachment F: Information Submitted for the Limestone Generating Station and the W A Parish Electric Generating Station
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.
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
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