Do all PM2.5 areas have to develop budgets for all PM2.5 precursor pollutants?
No. If through the SIP development process, on-road emissions of one or more precursors are determined to be a significant contributor to the PM2.5 nonattainment problem, an emissions budget for each of the relevant precursors must be established in the SIP. Alternatively, if through the SIP development process, emissions of one or more precursors are found to be insignificant, the PM2.5 SIP would not establish motor vehicle emissions budgets for such precursors, and regional emissions analyses for such precursors would not be required for subsequent conformity determinations. Please see the May 6, 2005 final rule for more information, available at: http://www.epa.gov/fedrgstr/EPA-AIR/2005/May/Day-06/a9086.htm.
