Nonattainment designations for PM2.5 became effective on April 5, 2005. There are 39 PM2.5 nonattainment areas comprised of 208 counties or partial counties. Currently, there are 87 PM10 nonattainment and maintenance areas, mostly in the Western United States.
Attainment and Nonattainment Areas in the U.S.: PM2.5 Standards
Attainment (or Unclassifiable) Areas (2,933 counties)
Nonattainment Areas (177 entire counties, 31 partial counties)
Conformity applies to metropolitan transportation plans and transportation improvement programs (TIPs), and FHWA and FTA projects in metropolitan and rural PM10 and PM2.5 nonattainment and maintenance areas. Key components of conformity are detailed in the Transportation Conformity Rule (40 CFR Parts 51 & 93) and include using the latest planning assumptions and emissions model, interagency and public consultation, timely implementation of transportation control measures in approved SIPs, regional emissions analysis, and in some cases localized or "hot-spot" analysis.
Transportation conformity for PM2.5 will apply one year from the effective date of nonattainment designations, or April 5, 2006. By that date, FHWA/FTA must determine conformity of metropolitan transportation plans and TIPs in PM2.5 nonattainment areas, or conformity will lapse. During a conformity lapse, FHWA/FTA funding and approvals are restricted to certain types of projects that are exempt from the conformity rule (i.e., safety projects, etc.), transportation control measures in approved SIPs, and project phases that have already been authorized. In addition, after April 5, 2006, project level conformity determinations must be made prior to final NEPA approval and or project authorizations for non-exempt Federal projects or project phases.
Once a SIP motor vehicle emissions budget is approved or found adequate by EPA, projected emissions from an area's planned transportation system must be no greater than the budget. Prior to an adequate or approved budget, it must be demonstrated that projected emissions from the planned transportation system are no greater than emissions from a "no-build" scenario, or no greater than emissions in a baseline year -- 1990 (PM10) or 2002 (PM2.5).