The Federal Aviation Administration Office of Environment and Energy has facilitated the characterization of gaseous and particle emissions from aircraft engines to enable development of technology-based emissions standards. As part of a broad emissions research portfolio, FAA funded research teams have acquired engine non-volatile particle emissions measurements from more than ten engine types in collaboration with the engine manufacturers. These data were used to inform the first non-volatile Particulate Matter (nvPM) mass concentration standard and the Landing-Take Off nvPM mass and number standards. The FAA has funded research to measure ambient concentration of pollutants to quantify aircraft contribution to ambient pollutant concentrations. These efforts seek to collect comprehensive data including particle size distribution and meteorological conditions to inform the development of statistical and physical-chemical models. While significant advances have been made, there are still a number of gaps that need to be addressed. The methodology to estimate cruise nvPM emissions remains empirical with little or no data available to validate the approach. In addition, newer lean-burn engines present a technical challenge in using the current methodology. Quantifying cruise nvPM emissions is critical to understand the role of nvPM emissions in the formation of contrail ice particles and to characterize the impact of alternative jet fuels on contrails. Related to this is the role of ambient conditions in the formation of nvPM emissions in gas-turbine engines. Research is also needed to evaluate and improve airport air quality compliance models.