Citation:

U.S. EPA. Integrated Review Plan for Oxides of Nitrogen National Ambient Air Quality Standards. Volume 2: Planning for the Review and the Integrated Science Assessment. U.S. Environmental Protection Agency, Washington, DC, EPA/452/R-24/010b, 2024.

Impact/Purpose:

The Integrated Review Plan (IRP) (this document) is developed during the NAAQS review process. The three volumes that make up this document collectively outline the timeline and key policy-relevant issues and scientific questions for how the relevant NAAQS criteria pollutant will be reviewed. Volume 2 of the IRP addresses the general approach for review and planning for the ISA and will be reviewed by CASAC. Volume 2 of the IRP will be submitted as a subproduct under product HERA 401.1.7.

Description:

The U.S. Environmental Protection Agency (EPA) is conducting a review of the health-based air quality criteria and the primary (health-based) national ambient air quality standards (NAAQS) for oxides of nitrogen. Ambient concentrations of oxides of nitrogen are influenced by both direct nitrogen dioxide (NO2) emissions and by emissions of nitric oxides (NO), with the subsequent conversation of NO to NO2 primarily through reaction with ozone (O3).  Consistent with the reviews completed in 2010 and 2018, this review focuses on health effects associated with gaseous oxides of nitrogen3 and the protection afforded by the primary NO2 standards. The gaseous oxides of nitrogen include NO2 and NO, as well as their gaseous reaction products. Total oxides of nitrogen include these gaseous species as well as particulate species (e.g., nitrates). Health effects and non-ecological welfare effects associated with the particulate species are addressed in the review of the NAAQS for particulate matter (PM).4 The EPA is separately reviewing the ecological welfare effects associated with and the secondary standards for oxides of nitrogen, oxides of sulfur, and PM.5  This Volume (2) of the integrated review plan (IRP) contains the current plans for the general approach for the review, as well as key planning considerations for the development of the integrated science assessment (ISA). The NAAQS review process provides an integrative assessment of relevant scientific information and will focus on key aspects of the NAAQS, including the basic elements of the standards: the indicator,6 averaging time, form,7 and level. These elements, which together serve to define each ambient air quality standard, are considered collectively in evaluating the protection to public health afforded by the standards.  This document is the second of three volumes that will comprise the IRP for the primary NO2 NAAQS review. Volume 1 includes introductory or background information on the legislative requirements for reviews of the NAAQS, an overview of the review process, background information on prior reviews of the health-based air quality criteria and primary standards for oxides of nitrogen and a summary of key aspects of the basis for the existing primary NO2 NAAQS, and a summary of the status and anticipated milestones for the current review. Volume 1 also includes an appendix that includes an overview of the key aspects of existing ambient air monitoring requirements for NOX. Volume 2 (this document) presents the general approach for this review, the policy-relevant questions guiding the review, and the plans for the development of the ISA. Specifically, Chapter 2 of Volume 2 outlines the general approach of the NAAQS review and details a set of policy-relevant questions intended to focus this review on the critical scientific and policy issues. Chapter 3 of Volume 2 presents plans for the ISA, including the document organization, scope, and specific questions for consideration in light of the overarching policy-relevant questions for the review. Together, Volumes 1 and 2 provide the current information regarding this review of the primary NAAQS for oxides of nitrogen. Volume 3 of the IRP, the planning document for quantitative analyses to be considered in the policy assessment (PA), will be developed with consideration of the availability of new evidence as identified in the development of the ISA. Accordingly, the public release of Volume 3 of the IRP will generally coincide with that of the draft ISA and it will be the subject of a consultation with the CASAC at that time.

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