November 28, 1995

EP A-S AB-C AS AC-LTR-96-001

Honorable Carol M. Browner
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC  20460

        RE:  CASAC Closure on the Air Quality Criteria for Ozone and Related
             Photochemical Oxidants

Dear Ms. Browner:

  A Panel of the Clean Air Scientific Advisory Committee (CASAC) of EPA's Science
Advisory Board (SAB) met on July 20  and 21, 1994 and March 21 and 22, 1995, to review drafts
of the document entitled Air Quality Criteria for Ozone and Related Photochemical Oxidants. At
these meetings and in subsequent written comments, the Committee made extensive
recommendations for strengthening the document. In August 1995, revisions to the Criteria
Document were mailed to the CASAC members for review.  On September 19, 1995, the Panel
met to complete this review. The resulting comments by the Committee members note with
satisfaction the improvements made in the scientific quality and completeness of the Criteria
Document.  The changes are consistent with CASAC's recommendations.

  At the September 1995 meeting the  Panel came to closure on the Criteria Document.  It
was the consensus of the Panel members that the Criteria Document provides an adequate
review of the available scientific data and relevant studies of ozone and related photochemical
oxidants. The document is quite comprehensive and will provide an adequate scientific basis for
regulatory decisions on ozone and related photochemical oxidants based on available
information.  At the meeting and subsequently in writing, Panel members provided the Agency
with additional comments for consideration. Most of these comments were directed at Chapter
5, the ecological effects chapter. Although the Panel would like to have these comments
considered for incorporation in the Criteria Document, the Panel did not feel that it was
necessary to review another revised version.

   On behalf of the Panel, I would like to thank EPA staff for their efforts in preparing the
Criteria Document on the accelerated schedule.  Our comments on the OAQPS Staff Paper will
follow shortly.

                                        Dr. George T. Wolff, Chair
                                Clean Air Scientific Advisory Committee