Over the past decade, the U.S. Environmental Protection Agency (EPA) in cooperation with state and local agencies has developed a National Emission Inventory (NEI) for fine particulate matter (PM) (EPA, 2001). In addition, the EPA has been developing the Community Multiscale Air Quality (CMAQ) model for the mechanistic prediction of gas and aerosol-phase pollutant concentrations (Byun and Ching, 1999). In the present work, an extension to the CMAQ model is described that allows the user to track the emissions from an arbitrary number of primary aerosol sources as they are transported through the atmosphere. The model is coupled with the National Emissions Inventory (NEI) NEI to estimate primary carbonaceous aerosol concentration increments contributed by nine major emission categories over the continental U.S. from June 15 August 31, 1999. Model results are evaluated against source-specific molecular measurements collected at eight receptor sites in the southeastern U.S.