Air Pollution from Sulfur Dioxide
- What is sulfur dioxide?
- 2010 SO2 National Ambient Air Quality Standard
- Latest air quality planning that addresses the standards for sulfur dioxide
- Related Web pages and publications
- Get more information on the Texas SIP and contact the TCEQ
What is sulfur dioxide?
Sulfur dioxide (SO2) is one of a group of highly reactive gases called sulfur oxides (SOX). SO2 is the component of greatest concern and is used as the indicator for the larger group of SOX. Other gaseous sulfur oxides are found in the atmosphere at concentrations much lower than SO2, and emissions that lead to high concentrations of SO2 generally also lead to the formation of other SOX. Control measures that reduce SO2 emissions generally reduce exposure to all gaseous SOX.
Exposure to SO2 has been linked with a number of adverse effects on the respiratory system, especially for people with asthma, at elevated ventilation rates. Studies also 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. Further, SOX can also react with other compounds in the atmosphere to form small particles that can cause or worsen respiratory disease and aggravate existing heart disease.
The largest source of SO2 emissions is fossil-fuel combustion at power plants and other industrial facilities. Smaller sources of SO2 emissions include extraction of metal from ore and burning of high-sulfur fuels by locomotives, large ships, and non-road equipment.
2010 SO2 National Ambient Air Quality Standard
The United States Environmental Protection Agency (EPA) issued the final SO2 rule to strengthen the primary NAAQS on June 2, 2010 (published June 22, 2010 in 75 FR 35520).
Effective August 23, 2010, the rule introduced a new one-hour SO2 primary standard, met when the three-year average of the 99th percentile of the annual distribution of daily maximum one-hour average SO2 concentrations does not exceed 75 (parts per billion (ppb).
The 2010 SO2 NAAQS final rule established required minimum SO2 air quality monitoring locations fully operational by January 1, 2013, in Amarillo (1), Austin-Round Rock (1), Beaumont-Port Arthur (1), Dallas-Fort Worth-Arlington (2), Houston-Sugar Land-Baytown (2), Longview (1), San Antonio (2), and El Paso (1).
The EPA expects the one-hour standard to better protect the public from exposure to high short-term concentrations and to protect communities located close to coal-fired power plants, industrial boilers, petroleum refineries, metal processing plants, and diesel exhaust. The EPA revoked previously existing SO2 annual and 24-hour primary standards, effective one year after area designations are final, as no protection beyond that achieved by the new 75 ppb standard is indicated. Final area designations are expected by June 2, 2012.
The EPA anticipates an implementation approach for the 2010 SO2 standard using refined air dispersion modeling of medium and large SO2 sources and air quality monitoring of smaller emission sources to determine an area’s compliance status. The EPA indicates that under this approach, areas with any monitoring data or modeling results violating the standard will be designated nonattainment, areas with both monitoring data and modeling results indicating no violation will be designated attainment, and all other areas will be designated unclassifiable.
For the 2010 SO2 NAAQS, the EPA will require states with areas designated nonattainment to submit attainment demonstration SIPs by February 2, 2014, showing the standard will be met in those areas by August 2, 2017. For areas designated attainment or unclassifiable, states will be required to submit SIPs fulfilling Federal Clean Air Act §110(a)(1) infrastructure requirements to the EPA by June 2, 2013. The EPA expects states to include demonstrations of expeditious attainment and maintenance of the 2010 standard in their infrastructure plans for unclassifiable areas and attainment areas. SIPs addressing §110(a)(2)(D)(i) transport requirements for the 2010 SO2 primary NAAQS are also due to the EPA by June 2, 2013. The EPA expects to issue guidance in mid-2011 for states to develop SIPs for the 2010 SO2 NAAQS, and plans to seek public comment before finalizing in August 2011.
For more information on the new EPA one-hour SO2 standard, please visit the EPA's Web page: Primary NAAQS for Sulfur Dioxide
Latest air quality planning that addresses the standards for sulfur dioxide
Last updated: 6/22/2011
Designation Recommendation for 2010 One-hour SO2 Primary NAAQS Approved
At the April 20, 2011, TCEQ agenda, the commission approved the executive director’s recommended designations for Texas counties under the one-hour SO2 Primary NAAQS. The governor submitted the designation recommendation to the EPA in a letter dated June 2, 2011.
The EPA issued guidance in March 2011 for states to determine attainment status and recommend area designations under the new standard. The guidance includes information regarding AERMOD, the air dispersion model the EPA now requires for SO2 air quality modeling. The EPA expects states to base recommendations on 2008 through 2010 regulatory monitoring data. Final designations are expected from the EPA by June 2, 2012.
Public Meetings
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.
TCEQ Petition for Reconsideration of the Final Rule
On August 23, 2010, the TCEQ submitted a Petition for Reconsideration, asking the EPA to reconsider and stay the adoption and implementation of the final rule of the primary NAAQS for SO2. On January 18, 2011, the EPA filed a Denial of the Petitions to Reconsider the Final Rule Promulgating the Primary NAAQS for Sulfur Dioxide and Respondent’s Motion to Govern Further Proceedings in the United States Court of Appeals for the District of Columbia Circuit.
Texas’ Attainment Status for the SO2 NAAQS
No part of Texas is currently designated as nonattainment or in maintenance status for previous SO2 air quality standards, and attainment status for areas under the 2010 SO2 NAAQS has not yet been determined. The EPA anticipates issuing final area designations for the new SO2 NAAQS in June 2012.
Air quality monitoring data from existing regulatory monitors indicate that Jefferson County exceeded the 2010 SO2 primary NAAQS in 2009 with a one-hour design value (DV) of 80 ppb, and in 2010 with a one-hour DV of 77 ppb. One-hour SO2 DVs for all other Texas counties having at least one regulatory monitor indicate current attainment of the standard.
Adjustments have been made to the Texas SO2 monitoring network to ensure that new network design requirements are met.
Related Web pages and publications
- EPA General Page on Sulfur Dioxide
- Primary NAAQS for Sulfur Dioxide
- Secondary NAAQS for Sulfur Dioxide
- Complete List of Texas SIP Revisions
