D.	History of the Current Review
	The EPA initiated this current review in December 2005 with a call for information (70 FR 73236) for the development of a revised Integrated Science Assessment for Oxides of Nitrogen and Oxides of Sulfur- Ecological Criteria (henceforth the "ISA").  An Integrated Review Plan (IRP) was developed to provide the framework and schedule as well as the scope of the review and to identify policy-relevant questions to be addressed in the components of the review.  The IRP was released in 2007 (US EPA, 2007) for CASAC and public review.  EPA held a workshop in July 2007 on the ISA to obtain broad input from the relevant scientific communities.  This workshop helped to inform the preparation of the first draft ISA, which was released for CASAC and public review in December 2007; a CASAC meeting was held on April 2-3, 2008 to review the first draft ISA.  A second draft ISA was released for CASAC and public review in August 2008, and was discussed at a CASAC meeting held on October 1-2, 2008.  The final ISA (US EPA, 2008) was released in December 2008.  
	Based on the science presented in the ISA, EPA developed a Risk and Exposure Assessment for Review of the Secondary National Ambient Air Quality Standards for Oxides of Nitrogen and Oxides of Sulfur (henceforth the "REA") to further assess the national impact of the effects documented in the ISA.  The Draft Scope and Methods Plan for Risk/Exposure Assessment: Secondary NAAQS Review for Oxides of Nitrogen and Oxides of Sulfur outlining the scope and design of the future REA was prepared for CASAC and public in March 2008.  A first draft REA was presented to CASAC and the public for review in August 2008 and a second draft was presented for review in June 2009.  The final REA (US EPA 2009) was released in September 2009.  A first draft Policy Assessment was released in March 2010 and reviewed by CASAC on April 1-2, 2010.  In a June 22, 2010 letter to the Administrator, CASAC provided advice and recommendations to the Agency concerning the first draft Policy Assessment (Russell and Samet, 2010a).   A second draft Policy Assessment was released to CASAC and the public in September 2010 and reviewed by CASAC on October 6-7, 2010.  CASAC provided advice and recommendations to the Agency regarding the second draft Policy Assessment in a December 9, 2010 letter (Russell and Samet 2010b).  CASAC and public comments on the second draft Policy Assessment were considered by EPA staff in developing a final Policy Assessment (US EPA, 2011).  CASAC requested an additional meeting to provide additional advice to the Administrator based on the final Policy Assessment on February 15 - 16, 2011.  EPA released on January 14, 2011, the final Policy Assessment prior to final document production, to provide sufficient time for CASAC review of the document in advance of this meeting. A final Policy Assessment, incorporating final reference checks and document formatting, was released in February 2011.  In a May 17, 2011 letter (Russell and Samet, 2011a), CASAC offered additional advice to the Administrator with regard to recommendations and revisions to the secondary NAAQS for oxides of nitrogen and oxides of sulfur. 
      On February 3, 2006, the Center for Biological Diversity and four other plaintiffs filed an amended complaint alleging that EPA had failed to complete the current review within the period provided by statute.  The schedule for completion of this review is governed by a consent decree resolving that lawsuit and the subsequent extension agreed to by the parties. The schedule presented in the original consent decree that governs this review, entered by the court on November 19, 2007, was revised on October 22, 2009 to allow for a 17 month extension of the schedule.  The current decree provides that EPA sign for publication notices of proposed and final rulemaking concerning its review of the oxides of nitrogen and oxides of sulfur NAAQS no later than July 12, 2011 and March 20, 2012, respectively.  
	This action presents the Administrator's proposed decisions on the review of the current secondary oxides of nitrogen and oxides of sulfur standards.  Throughout this preamble a number of conclusions, findings, and determinations proposed by the Administrator are noted.  While they identify the reasoning that supports this proposal, they are only proposals and are not intended to be final or conclusive in nature.  The EPA invites general, specific, and/or technical comments on all issues involved with this proposal, including all such proposed judgments, conclusions, findings, and determinations.
