ACRP Report 6 provides guidance on the most important research needed by the airport community in the area of particulate emissions.  It examines the state of industry research on aviation-related particulate matter (PM) emissions and identifies knowledge gaps that existing research has not yet bridged.  These gaps and related research needs are then prioritized based on the ability of research in those areas to address airports’ needs for more thorough and accurate aviation-related PM emissions inventories.  While the main purpose of this report is to identify key research areas important to the airport community for ACRP consideration, research communities at large will also benefit from this report’s comprehensive analysis of aviation PM emissions-related research needs.