The document Compilation of Air Pollutant Emissions Factors (AP-42) has been published by the U. S. Environmental Protection Agency (EPA) since 1972. Supplements to AP-42 have been routinely published to add new emission source categories and to update existing emission factors. AP-42 is routinely updated by EPA to respond to new emission factor needs of EPA, State, and local air pollution control programs, and industry. An emission factor relates the quantity (weight) of pollutants emitted to a unit of activity of the source. The uses for the emission factors reported in AP-42 include: Estimates of areawide emissions; estimates of emissions for a specific facility; and evaluation of emissions relative to ambient air quality. The purpose of this report is to provide background information from test reports and other information to support revisions to AP-42 Section 11.1, Hot Mix Asphalt Production.