Emission and Formation\nof Aircraft Engine Oil Ultrafine\nParticles

Civil aviation gas turbine engines emit ultrafine particles\n(UFPs,\ndiameter < 100 nm). UFPs degrade air quality because they efficiently\ntransport their chemical content, including engine oil, into the body.\nYet, little is known about how and when oil containing UFPs are formed.\nResults here describe the thrust and flight phase-dependent oil emission\nand reveal the particle size-dependent transfer of vaporized oil to\nUFPs with molecular level resolution. All six engines studied emitted\noil containing UFPs. Lower volatility oil molecules are enriched on\nparticles <30 nm. Further, the particulate oil mass size distribution\naligns with the emitted surface area distribution, suggesting oil\nvapor condensation onto primary particles and the potential for oil\nnucleation. However, the oil gas-to-particle transfer in hot exhaust\nis likely incomplete at least 50 m downwind thus limiting current\nemission studies. The measured engine oil consumption provides an\nupper-limit oil emission index at idle of 240 mg oil per kg fuel.\nThe emission index at cruise is 110 mg kg<sup>–1</sup>, which\nis a factor of 10 greater than black carbon. For any flight >2\nh,\n95% of oil emission is expected to occur at cruise altitude, highlighting\nthe unknown effects of oil emission in the upper atmosphere.