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Air Quality: EPA's Integrated Science Assessments (ISAs)

Sulfur Dioxide- Health Criteria

Sulfur Oxides Primary - Health Criteria Report Cover
(PDF, 479 pp, 9 MB,
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The Issue
 Sulfur dioxide (SO2) is one of a group of highly reactive gases known as "oxides of sulfur. The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment. SO2 is linked with a number of adverse effects on the respiratory system particularly for exercising asthmatics. In 2010, EPA revised the primary (health-based) standard by establishing a one-hour standard at a level of 75 parts per billion (ppb).

EPA Action
EPA's NOx and SOx research efforts are focused on improving emissions estimates, determining health and ecological effects, and improving modeling capabilities. The Clean Air Act requires EPA to periodically review the science for six major air pollutants, including NOx and SOx. EPA's National Center for Environmental Assessment develops Integrated Science Assessments (ISAs) that summarize the science related to the health and ecological effects caused by these pollutants. ISAs provide a comprehensive review of the policy-relevant scientific literature published since the last National Ambient Air Quality (NAAQS) review and are a critical part of the scientific basis for establishing the NAAQS.¬†

In 2008, EPA released the Integrated Science Assessment for Oxides of Nitrogen- Health Criteria (Final) and the Integrated Science Assessment for Sulfur - Health Criteria (Final). But because of the overlap of these 2 air pollutants in the environment, the reports were combined into a single ecological criteria report, called the Integrated Science Assessment for Oxides of Nitrogen and Sulfur - Ecological Criteria (Final). [See the history of the pollutant reports for more detailed information on the NOx/SOx assessments]

[Update] EPA has initiated the next review of the primary SOX standard by issuing a call for information on recent research relating to the health effects of SOX and holding a workshop to discuss policy-relevant issues to be considered during the workshop. [Federal Register Notice May 10, 2013]

Workshop announcement:

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