The core of the Administrator’s rationale for tightening the ozone National Ambient Air Quality Standards (NAAQS) that is articulated in the US Environmental Protection Agency (EPA) Proposed Rule (79 Fed. Reg. 75234), is based on clinical studies of lung function responses to various levels of ozone. The specific measurement of lung function discussed is forced expiratory volume in one second (FEV1), and FEV1 changes are the lung function impact for which the Health Risk and Exposure Assessment (HREA) document provides quantitative risk estimates under alternative ozone NAAQS levels.

Analysis by Dr. Anne E. Smith and Dr. Garrett Glasgow finds that there is a large degree of both statistical and model uncertainty in the lung function decrements reported in the HREA, and that uncertainty undercuts the confidence in the projected reductions in lung function impacts that are described in the Proposed Rule.