In today's final action, EPA is retaining the existing nitrogen dioxide (NO<INF>2</INF>) increments as part of the Agency's regulations for the Prevention of Significant Deterioration (PSD) of air quality from emissions of nitrogen oxides (NO<INF>X</INF>). These regulations are designed to preserve the air quality in national parks and other areas that are meeting the national ambient air quality standards (NAAQS) for NO<INF>2</INF> (hereafter called the NO<INF>2</INF> NAAQS). EPA reevaluated the original NO<INF>2</INF> increments in response to a 1990 court ruling that directed the Agency to consider and harmonize the statutory criteria for establishing PSD regulations for NO<INF>X</INF> contained in sections 166(c) and 166(d) of the Clean Air Act (CAA or Act). EPA is also amending its PSD regulations to clarify that States otherwise meeting these requirements of the Act may obtain approval to employ alternative approaches to the existing increments for NO<INF>2</INF>. Under a separate action, we will be publishing a Supplemental Notice of Proposed Rulemaking (SNPR) to show how implementation of the model cap and trade program under the 2005 Clean Air Interstate Rule (CAIR) can meet the requirements for a State to use this approach in lieu of the existing NO<INF>2</INF> increments in order to prevent significant deterioration of air quality from emissions of NO<INF>X</INF>.