Integrated Science Assessment (ISA) for Sulfur Oxides – Health Criteria (Second External Review Draft, Dec 2016)

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This draft document provides EPA’s evaluation and synthesis of the most policy-relevant science related to the health effects of sulfur oxides. When final, it will provide a critical part of the scientific foundation for EPA’s decision regarding the adequacy of the current primary (health-based) National Ambient Air Quality Standard (NAAQS) for sulfur dioxide.

The references considered for inclusion in or cited in the external review draft ISA are available at

Sulfur oxides are one of six principal (or criteria) pollutants for which EPA has established NAAQS. For sulfur oxides, the indicator for the NAAQS is sulfur dioxide (SO2). The Clean Air Act requires EPA to periodically review the scientific basis for these standards by preparing an Integrated Science Assessment (ISA). These reviews play a significant role in EPA’s commitment to ensuring a clean and healthy environment for the public.

The draft ISA is part of the Agency’s periodic review of the primary (health-based) NAAQS for SO2. Overall, findings from recent studies strengthen the conclusions from the previous NAAQS review, which was completed in 2010. Results from recent studies strengthen the body of evidence indicating that short-term exposure to SO2 can cause respiratory effects, in particular, effects related to asthma exacerbation. There remains uncertainty regarding the potential for SO2 effects outside the respiratory system.


The intent of the ISA, according to the CAA, is to “accurately reflect the latest scientific knowledge expected from the presence of [a] pollutant in ambient air” (U.S. Code, 1970a, 1970b). It includes an assessment of scientific research from atmospheric sciences, exposure sciences, dosimetry, mode of action, animal and human toxicology, and epidemiology. Key information and judgments formerly found in the Air Quality Criteria Documents (AQCDs) for sulfur oxides (SOx) are included; Annexes provide additional details supporting the ISA. Together, the ISA and Annexes serve to update and revise the last SOx ISA which was published in 2008.


This draft will be reviewed by the Clean Air Scientific Advisory Committee (CASAC) at a public meeting announced in the Federal Register. A future Federal Register notice will inform the public of the exact date and time of that CASAC meeting. In revising and finalizing the ISA, EPA will take into account CASAC advice and recommendations as well as public comments. The final assessment, will be posted on EPA’s website, and will provide a critical part of the scientific foundation for the primary NAAQS for sulfur dioxide.


U.S. EPA. Integrated Science Assessment (ISA) for Sulfur Oxides – Health Criteria (Second External Review Draft, Dec 2016). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-16/351, 2016.


Date Description
15-May 2013EPA initiated the current review of the air quality criteria for SOX and the primary SO2 NAAQS, and also issued a call for information. [Federal Register Notice May 10, 2013]
16-Jun 2013EPA held a workshop entitled "Workshop to Discuss Policy-Relevant Science to Inform EPA's Integrated Plan for Review of the National Ambient Air Quality Standards for Sulfur Oxides" co-organized by EPA/ORD/NCEA and the EPA/OAQPS Staff to help with the development of future products on this subject matter. The workshop was held June 12-13, 2013, in Research Triangle Park, North Carolina. [Federal Register Notice May 10, 2013]
17-Mar 2014EPA released the Integrated Review Plan for the Primary National Ambient Air Quality Standard for Sulfur Dioxide – External Review Draft. [Federal Register Notice Mar 12, 2014]
18-Apr-Jul 2014CASAC held multiple public teleconferences to discuss the draft Integrated Review Plan. [Federal Register Notice Mar 25, 2014, Federal Register Notice May 27, 2014, Federal Register Notice Jun 18, 2014]
19-Jun 2014EPA held a public workshop to review initial draft materials to inform the development of the draft Integrated Science Assessment for Sulfur Oxides – Health Criteria.[Federal Register Notice Jun 12, 2014]
20-Oct 2014EPA released the final ‘Integrated Review Plan for the Primary National Ambient Air Quality Standard for Sulfur Dioxide' (EPA-452/R-14-007). [Federal Register Notice Nov 10, 2014]
21-Nov 2015EPA released the external review draft for public and independent peer review. [Federal register Notice Nov 24, 2015]
22-Dec 2015EPA announced a SAB advisory meeting to discuss the draft report in a December 21, 2015 Federal Register Notice. On December 24, 2015, EPA extended the public comment period adding an additional 30-days. The comment period is now February 24, 2016. [Federal Register Notice Dec 24, 2015]
23-Dec 2016EPA released the second external review draft for public and independent peer review. [Federal Register Notice Dec 9, 2016]
24-May 2017EPA announced a SAB public teleconference call on June 20, 2017 to discuss the second draft report. [Federal Register Notice May 23, 2017]

This download(s) is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by EPA. It does not represent and should not be construed to represent any Agency determination or policy.


Comments on the assessment may be submitted and reviewed using the Docket ID EPA-HQ-ORD-2013-0357