Air Quality Criteria for Sulfur Oxides

As described in the attached comments, this second draft of the SOx ISA is inaccurate, unclear and biased in several ways. Key among these issues: • The SOx ISA inappropriately concludes there is adequate evidence to infer a causal relationship between sulfur dioxide (SO2) and a variety of morbidity endpoints. API finds that the SOx ISA fails to acknowledge the single study of which API is aware that examines hospital admissions for asthma in association with elevated 5-minute SO2 exposures – that study found no association. • Similarly, the SOx ISA inappropriately concludes the evidence is suggestive of a causal association between short-term exposure to SO2 and premature mortality. Since EPA acknowledges within the SOx ISA that the two major North American studies indicted no evidence of an association with SO2 and short-term mortality, API questions how this conclusion is supported.

API concludes that significant revision of the SOx ISA is necessary. As drafted, the SOx ISA is inaccurate, unclear and biased in several ways. It mischaracterizes the extent to which ambient measurements of sulfur dioxide (SO2) used in epidemiological studies are a good surrogate for personal SO2 exposures. It fails to explain adequately how studies were selected for inclusion and how the cited results from those studies were determined. It does not follow its own guidelines concerning which studies are most relevant. It cherry-picks among results of the studies discussed. It reinterprets without adequate justification conclusions of study authors and offers interpretations of studies contradictory to those that it has offered in reviewing other National Ambient Air Quality Standards (NAAQS). It ignores the importance of statistical significance in assessing whether a study provides evidence of an association between SO2 and a health response. As a result, it inaccurately characterizes the epidemiological evidence as suggesting that ambient SO2 levels below the current standard cause increased respiratory symptoms, increased emergency department visits and hospital admissions and acute mortality. Finally, it offers science policy judgments that should be reserved for the Administrator.