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The United States Environmental Protection Agency (“EPA”) published an April 18th Federal Register Notice addressing the National Ambient Air Quality Standard ("NAAQS") for Nitrogen Dioxide(“NO₂”). See 83 Fed. Reg. 17226.

EPA states that it has decided to retain the current NAAQS for NO₂.

The Clean Air Act uses a two-prong approach to air pollution control.

First, NAAQS are set for a limited number of pollutants. Section 108 of the Clean Air Act requires that EPA identify air pollutants which may be reasonably be anticipated to endanger the public health and welfare and to issue air quality criteria for them.

Second, Section 109 requires that EPA promulgate primary and secondary NAAQS for the pollutants identified under Section 108. Section 109(b)(1) defines a primary standard as “the attainment and maintenance which, in the judgment of the Administrator, based on the criteria allow in an adequate margin of safety, or requisite to protect the public health.”

The states are primarily responsible for ensuring the attainment and maintenance of NAAQS once the EPA has established them. Each state is required to formulate, subject to EPA approval, an implementation plan designed to achieve each NAAQS (including revisions).

The Clean Air Act requires that EPA periodically review both the air quality criteria and the NAAQS. The most recent review for NO₂ was undertaken pursuant to a schedule set by a federal court. It mandated a final EPA decision by April 6th. EPA previously completed a review of the primary NO₂ NAAQS in 2010.

EPA states that it is retaining the current primary NO₂ standards without revision. It further states that the decision:

. . . has been informed by a careful consideration of the full body of scientific evidence and information available in this review, giving particular weight to the assessment of the evidence in the 2016 NO_x Integrated Science Assessment (ISA); analyses and considerations in the Policy Assessment (PA); the advice and recommendations of the Clean Air Scientific Advisory Committee (CASAC); and public comments.

A link to the Federal Register Notice can be found here.