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and10-m sampling rakes contained multiple gasandparticle inlet probes to facilitate astudy of the spatial variation of emissions across the engine exhaust plane. Gas-phase emission indices measured at 1 m were in good agreement withtheenginecertificationdataaswellaswithpredictionsprovidedbytheenginecompany.However,atlowpower settings, trace-species emissions were observed to be highly dependent on ambient conditions and engine temperature. Nonvolatile particles emitted by the engine exhibited a log-normal size distribution that peaked between 15 and 40 nm, depending on engine power. Samples collected 30 m downstream of the engine exit plane exhibited a prominent nucleation mode, indicating that secondary aerosols composed of sulfuric acid and low- volatility organic species formed rapidly within the plume as it expanded and cooled. Black carbon emissions were a minimum at approach and a maximum at climb and takeoff engine power settings. Black carbon dominated total mass emissions at high thrust, whereas volatile particles contributed an equal or perhaps greater fraction at low- to midpower settings. Although variations in fuel aromatic content had no discernible impact on particle emissions, volatile particle number and mass concentrations in aged exhaust plumes were highly sensitive to the fuel sulfur content.