Aerodyne is developing a sulfate detection instrument, based on the Tunable Infrared Laser Differential Absorption Spectrophotometer (TILDAS) technology and therefore termed the "TILDAS-sulfate" instrument, for measurement of the size-resolved sulfate PM emissions of aircraft engine combustion. Over the past 10 years and through a series of NASA led efforts, the Aerodyne Research Inc emissions team has made a series of contributions to on-going NASA programs to characterize aircraft engine emissions. Despite progress, significant knowledge gaps exist especially for combustion emissions of alternatives to petroleum jet fuel. During this SBIR effort, we tested instrument performance in the absence of interferences, in the presence of >20-fold excess sulfur dioxide interference, in the presence of a combustion gases containing nitrogen oxide and hydrocarbons as potential interferences, and for particles ranging in size from 100 to 300 nm. Instrument sensitivity was shown to be at least 600 ng per meter cubed (on a 1-sec cycle). In Phase II, we plan to: upgrade the instrument and incorporate improvements to Aerodyne's TILDAS technology to improve the detection limit to as low as 60 ng per meter cubed on a 1-sec data acquisition cycle; test the upgraded instrument in the laboratory; demonstrate the instrument in the field for characterization of aircraft engine particle emissions.