This draft Staff Paper, prepared by staff in the U.S. Environmental Protection Agency's (EPA) Office of Air Quality Planning and Standards (OAQPS), evaluates the policy implications of the key studies and scientific information contained in the draft document, Air Quality Criteria for Ozone and Related Photochemical Oxidants: 2nd External Review Draft (USEPA, 2005b; henceforth referred to as the draft CD), prepared by EPA's National Center for Environmental Assessment (NCEA). This draft Staff Paper also presents and interprets initial results from several staff analyses (e.g., air quality analyses, human exposure analyses, and human health risk assessments) and discusses plans for a staff environmental assessment of vegetation-related impacts. Staff believes that these analyses should be considered in EPA's current review of the national ambient air quality standards (NAAQS) for ozone (O(sub 3)). This draft Staff Paper identifies alternative standard options for purposes of conducting additional exposure and risk analyses but does not present staff conclusions and recommendations as to potential revisions of the primary (health-based) and secondary (welfare-based) O(sub 3) NAAQS. The policy assessment to be presented in the final version of this Staff Paper is intended to help 'bridge the gap' between the scientific review contained in the draft CD and the judgments required of the EPA Administrator in determining whether it is appropriate to revise the NAAQS for O3. Emphasis will be placed on identifying those conclusions and uncertainties in the available scientific literature that the staff believes should be considered in selecting an indicator, averaging times, forms1, and levels for the primary (health-based) and secondary (welfare-based) standards, which must be considered collectively in evaluating the health and welfare protection afforded by O3 standards. The final Staff Paper will evaluate the policy implications of the key studies and scientific
information contained in the final CD (targeted for completion by February 2006), identify the critical elements that EPA staff believes should be considered in the current review of the NAAQS for O3, and present factors relevant to the evaluation of current primary and secondary O3 NAAQS, as well as staff conclusions and recommendations of options for the Administrator to consider.