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SUPPLEMENTARY INFORMATION:

Information About the Document

Section 108(a) of the Clean Air Act directs the Administrator to identify certain pollutants that, among other things, “cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare” and to issue air quality criteria for them. Further, section 108(a)(2) of the Act provides that these air quality criteria are to “accurately reflect the latest scientific knowledge useful in indicating the kind and extent of all identifiable effects on public health or welfare which may be expected from the presence of [the] pollutant in the ambient air . . . .” Under section 109 of the Act, the EPA is then to establish National Ambient Air Quality Standards (NAAQS) for each pollutant for which the EPA has issued criteria. Section 109(d) of the Act subsequently requires periodic review and, if appropriate, revision of existing air quality criteria to reflect advances in scientific knowledge on the effects of the pollutant on public health or welfare. The EPA is also required to review and, if appropriate, revise the NAAQS, based on the revised air quality criteria (for more information on the NAAQS review process, see http://www.epa.gov/​ttn/​naaqs/​review.html).

Oxides of nitrogen are one of six criteria pollutants for which EPA has established NAAQS. Periodically, EPA reviews the scientific basis for these standards by preparing an ISA (formerly called an Air Quality Criteria Document). The ISA, in conjunction with additional technical and policy assessments, provides the scientific basis for decisions by EPA on the adequacy of the current NAAQS and the appropriateness of possible alternative standards. The Clean Air Scientific Advisory Committee (CASAC), an independent science advisory committee with review and advisory functions mandated by section 109(d)(2) of the Clean Air Act, is charged with, among other things, independent scientific review of the EPA's air quality criteria.

On February 10, 2012 (77 FR 7149), EPA formally initiated its current review of the air quality criteria for the health effects of oxides of nitrogen and the primary (health-based) nitrogen dioxide (NO₂) NAAQS, requesting the submission of recent scientific information on specified topics. EPA held a workshop on February 29 to March 1, 2012, to gather input from scientific experts, both internal and external to EPA, as well as from the public regarding key science and policy issues that will frame the review of the health effects of the oxides of nitrogen and the primary NO₂ NAAQS (77 FR 7149).

The discussions at this workshop guided the development of the EPA's “Draft Plan for Development of the Integrated Science Assessment for Nitrogen of Oxides—Health Criteria,” a draft “Integrated Review Plan for the Primary NAAQS for Nitrogen Dioxide” (EPA-452/R-14-003), and initial draft materials for the development of the ISA. The draft plan for the development of the ISA was made available for public comment on May 3, 2013 (78 FR 26026), and was discussed by the CASAC via a publicly accessible teleconference consultation on June 5, 2013 (78 FR 27234). On June 11, 2013, EPA held a workshop to discuss, with invited scientific experts, initial draft materials prepared for the development of the ISA (78 FR 27374). The draft Integrated Review Plan (IRP) was made available in February 2014 for comment by the public and review by the CASAC (79 FR 7184) and was reviewed by the CASAC at a public meeting on March 12, 2014 (79 FR 8701). The CASAC panel provided a consensus letter for their review of the draft IRP to the Administrator of the EPA on June 10, 2014 (http://yosemite.epa.gov/​sab/​sabproduct.nsf/​264cb1227d55e02c85257402007446a4/​89989229944F36B085257CF300692E2A/​$File/​EPA-CASAC-14-001+​unsigned.pdf). The final IRP was released in June 2014 (79 FR 36801), and is available at: http://www.epa.gov/​ttn/​naaqs/​standards/​nox/​s_​nox_​2012_​pd.html.

Comments on the draft plan for the ISA and discussion at the June 11, 2013, workshop guided development of the “First External Review Draft Integrated Science Assessment for Oxides of Nitrogen—Health Criteria,” which was released on November 22, 2013 (78 FR 70040), and is available at: http://cfpub.epa.gov/​ncea/​isa/​recordisplay.cfm?​deid=​259167. The CASAC review panel for the oxides of nitrogen met at a public meeting on March 12-13, 2014, to review the draft ISA along with the draft IRP (79 FR 8701). Subsequently, on June 10, 2014, the CASAC panel provided a consensus letter for their review to the Administrator of the EPA (http://yosemite.epa.gov/​sab/​sabproduct.nsf/​264cb1227d55e02c85257402007446a4/​15E4619D3CD3409A85257CF30069387D/​$File/​EPA-CASAC-14-002+​unsigned.pdf). The second external review draft ISA was developed with consideration of comments received from the CASAC and the public on the first external review draft ISA and evaluated scientific studies published through August 2014. The CASAC panel met at a public meeting on June 2-3, 2015, to review the second draft ISA (79 FR 22993). Subsequently, on September 9, 2015, the CASAC provided a consensus letter for their review to the Administrator of the EPA (http://yosemite.epa.gov/​sab/​sabproduct.nsf/​6612DAF24438687B85257EBB0070369C/​$File/​EPA-CASAC-15-001+​unsigned.pdf). The letters from the CASAC, as well as public comments received on the ISA drafts, can be found in Docket ID No. EPA-HQ-ORD-2013-0232.

EPA has considered comments by the CASAC panel and by the public in preparing this final ISA.