The EPA on Thursday, June 3, 2010, finally issued its new one-hour standard for SO₂. Characterized by the agency as "taking on an old problem in a new way," the regulation will replace the current 24-hour and annual SO₂ standards, setting a one-hour allowable level of 75 parts per billion (ppb). The rule also comes with a new Air Quality Index and monitoring requirements.

The agency noted that its final rule addresses only the SO₂ primary standards, which are designed to protect public health. The EPA said it will address the secondary standard – designed to protect the public welfare, including the environment – as part of a separate review to be completed in 2012. The agency expects to identify or designate areas not meeting the new primary standard by June 2012.

"Moving to a one-hour standard and monitoring in the areas with the highest SO2 levels is the most efficient and effective way to protect against sulfur dioxide pollution in the air we breathe," said EPA Administrator Lisa P. Jackson.  

New Monitoring Requirements

The EPA also announced it is changing the monitoring requirements for SO₂. The new requirements will require that monitors will be placed where SO₂ emissions impact populated areas. Any new monitors required by this rule must begin operating no later than Jan. 1, 2013. The agency said it is expecting to use modeling as well as monitoring to determine compliance with the new standard.

According to the agency's website, designations for the revised standard would rely upon the monitors currently in place that evaluate area-wide concentrations of SO₂ as well as available modeling data indicating a violation of the standard. While the agency's monitors will remain the same, many in industry will need to update their monitoring systems and equipment in order to ensure a one-hour standard is being maintained.

State Implementation Plans designed to reduce emissions in areas designated as nonattainment will be due within 18 months of the effective date of designation, and the attainment date for nonattainment areas will be within five years of designation.  

Gone are 24-hour and Annual Standards

  The one-hour SO₂ health standard of 75 ppb was, according to the agency, designed to protect against short-term exposures ranging from five minutes to 24 hours. The agency is revoking the current 24-hour and annual SO₂ health standards because, according to an agency release, "the science indicates that short-term exposures are of greatest concern and the existing standards would not provide additional health benefits."

The first National Ambient Air Quality Standards for SO2 were set in 1971, establishing both a primary standard to protect health and a secondary standard to protect the public welfare. The last review of the SO₂ NAAQS was completed in 1996 and the agency chose not to revise the standards. In the last review, the agency also considered, but did not set, a five-minute NAAQS to protect asthmatics at elevated ventilation rates from bronchoconstriction and respiratory symptoms associated with five- to 10-minute peaks of SO₂.

More information on the new SO₂ primary standard is available at  www.epa.gov/ttn/naaqs/standards/so2/s_so2_index.html.

Read the EPA's press release at http://yosemite.epa.gov/opa/admpress.nsf/6424ac1caa800aab85257359003f5337/f137260029b9b4f385257737004e521b!OpenDocument

Related articles:

• Public hearings in January
• Public CASAC review in March
• 100% of Power industry met standards in '08
• Cap-and-Trade Auction in 2009
• February 2007 feature on emissions trading
• Bob McIlvaine on monitoring pitfalls for SO₂ and NO_X
• Agency announces intent to control SO₂ from Thermal Dryers

SOURCES: EPA press release, Past PE coverage of SO2 standards, EPA website