Comment submitted by Ted Steichen, Advisor, Regulatory and Scientific Affairs, American Petroleum Institute (API)

API finds that the clinical and epidemiological data in the REA do not support the US EPA suggested 1-hour daily maximum SO2 NAAQS 50-150 ppb. For the following reasons explained in the attached comments: (1) The clinical SO2 data are based on sensitive sub-populations (exercising adult and adolescent asthmatics), in a rare exposure scenario, in which symptoms (if they occur) can be relieved by discontinuing exercise. Statistically and biologically-relevant lung function effects attributable to SO2 do not occur at exposures < 400 ppb, (2) The use of clinical data makes the use of safety factors for sensitive individuals, non- human data, use of a LOAEL, and use of chronic exposures unnecessary, and (3 ) epidemiological studies provide inadequate support for the proposed standard owing to their many limitations, including exposure misclassification, measurement error, confounders, weak and inconsistent findings within and among studies, and incoherence with clinical studies.