In both PM10 and PM2.5 areas, directly emitted PM from motor vehicle tailpipes, as well as from normal brake and tire wear, must be considered in conformity. In addition, in PM10 areas, VOCs and/or NOx are considered if EPA or the State air agency finds that they are a significant contributor to the PM10 problem. In PM2.5 areas, NOx must be considered unless EPA and the State air agency find that it is not a significant contributor to the PM2.5 problem. VOCs, SOx, and NH3 are to be considered in PM2.5 areas, only if EPA or the State air agency finds that they are significant contributors to the PM2.5 problem. Once submitted SIP budgets are found adequate or approved, only those precursors that have identified budgets in the SIP need to be considered in conformity.
For PM10 areas, road dust from paved and unpaved roads should be included in all regional emissions analyses. For PM2.5 areas, road dust is included before a SIP is submitted and budgets are found adequate or approved if EPA or the State air agency finds that it is a significant contributor to the PM2.5 problem. After a SIP budget is found adequate or approved, road dust is included in the PM2.5 regional emissions analysis if the budget includes road dust.
Dust from transit and highway project construction in PM10 and PM2.5 areas must only be included in the regional emissions analysis if the SIP identifies it as a contributor (PM10) or significant contributor (PM2.5) to the nonattainment problem.
Estimates of vehicle miles traveled (VMT) are multiplied by emission factors from EPA's latest approved emissions model to estimate PM emissions. Emissions from exhaust, and tire and brake wear, as well as applicable precursor emissions are currently estimated using MOBILE6.2 (EMFAC 2002 in California). In certain areas, estimates of dust from roads and construction may be required using EPA's AP-42 methodology.
Qualitative localized, or hot-spot, analysis is required for all non-exempt FHWA and FTA projects in PM10 nonattainment and maintenance areas. In addition, quantitative analysis may be required for PM10 once EPA develops guidance. As of January 2006, EPA has not yet finalized any regulatory requirements for hot-spot analysis in PM2.5 areas.
Interagency consultation will play an important role in making transportation conformity determinations in the PM2.5 nonattainment areas. Typical issues for interagency discussion include:
PM emissions can be reduced in a number of ways, such as more stringent standards for engines and fuels, diesel retrofit programs, accelerated retirement programs, and idling-reduction programs. Other control measures that can be implemented locally include diesel retrofits of buses and trucks, on-road street sweepers and paving non-paved roads. Research is underway to identify other cost effective strategies that transportation agencies could implement to reduce PM.