EPA Reviews 1971 Air Quality Standards for Sulfur Dioxide
The current National Ambient Air Quality Standards (NAAQS) for sulfur dioxide were set in 1971 based on a Criteria Document published in 1969 by the Department of Health Education and Welfare. The scientific articles considered in the original Criteria Document predate 1968. In 1971, the newly established EPA set the first primary sulfur dioxide NAAQS: an annual average standard of 0.03 ppm (80 µg/m3); and a 24-hour standard of 0.14 ppm (365 µg/m3). The current standards are based on 40 plus year old science.
Following the promulgation of the initial sulfur dioxide standards, a series of clinical chamber studies established that that low level exposures to sulfur dioxide — for periods as short as five minutes — can be harmful to the health of people with asthma. EPA completed a review of these studies in a 1982 Criteria Document. An addendum to the Criteria Document, summarizing 16 additional controlled studies of asthmatics under exercise conditions, was published in a 1986. In 1994, EPA published a supplement to update the Criteria Document addendum.
Additionally, in the intervening years we have amassed new epidemiological studies that indicate respiratory effects at levels well below the current standards.
Ultimately, in 1996, the Agency decided not to revise the standards based primarily on the results of the exposure assessment. The exposure assessment relied on numerous assumptions about emissions, ambient concentrations, activity patterns, breathing rates, and even medication use. The cynical reasoning was that very few asthmatics were predicted to be exercising in the vicinity of a power plant plume, and if they were, they could take medication to relieve their symptoms.
The American Lung Association challenged the EPA’s failure to set a short-term standard for sulfur dioxide in federal court, and in 1999, the court ruled in the American Lung Association’s favor and sent the rule back to EPA for a rewrite.
Now, ten years later, EPA is in the midst of its review of the 1971 standards. As part of the review, EPA is preparing two documents — an Integrated Science Assessment and a Risk and Exposure Assessment — that will form the basis for a subsequent policy assessment.
The American Lung Association testified on EPA’s draft Integrated Science Assessment and draft Risk and Exposure Assessment at a July 30-31, 2008 meeting of the Clean Air Scientific Advisory Committee (CASAC). A copy of the Lung Association statement is attached below.
Copies of the draft EPA documents are available online at: http://epa.gov/ttn/naaqs/standards/so2/s_so2_index.html
Information on the CASAC review is available online at: http://yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/DA44325F1D9F4CF4852573CA
005FF9FE?OpenDocument
The next step in the process will be the publication of a final Integrated Science Assessment and a second draft Risk and Exposure Assessment which will be subject to CASAC and public review. EPA is slated to issue a policy assessment (know as the “Advanced Notice of Proposed Rulemaking”) in February 2009, with a CASAC and public review in April 2009.
EPA is on a court-ordered schedule to proposed revisions to the standards by July 30, 2009 and to issue final rulle by March 2010.
