Transportation Conformity Rule Amendments for the New PM2.5 National Ambient Air Quality Standard: PM2.5 Precursors

This final rule adds the following transportation-related PM<INF>2.5</INF> precursors to the transportation conformity regulations: nitrogen oxides (NO<INF>X</INF>), volatile organic compounds (VOCs), sulfur oxides (SO<INF>X</INF>), and ammonia (NH<INF>3</INF>). The final rule specifies when each of these precursors must be considered in conformity determinations in PM<INF>2.5</INF> nonattainment and maintenance areas before and after PM<INF>2.5</INF> state air quality implementation plans (SIPs) are submitted. Today's action also makes a technical correction to a cross- reference of the U.S. Department of Transportation's (DOT) planning regulations in the public consultation procedures of the conformity rule. The Clean Air Act requires federally supported highway and transit projects to be consistent with ("conform to") the purpose of a SIP. EPA has consulted with DOT on the development of this final rule and DOT concurs with its content.