The potential impact of aircraft gas turbine engine emissions upon the atmosphere has become increasingly apparent. Particulate matter (PM) emissions such as black carbon soot particles are the products of combustion processes. Modern airplane engines require lubrication systems. These are not typically considered as sources of PM emissions, but due to their low volatility, any emitted oil vapor or drops will add to the condensed mass and contribute to the organic PM in the wake of the aircraft. The highly efficient fuel combustion of modern aircraft engines significantly reduces PM emissions, therefore emissions from the lubrication system can be a significant contributor to the overall emission signature.

Zhenhong Yu, Aerodyne Research, Inc., Billerica, Massachusetts, USA, and colleagues investigated characteristic ion fragmentation patterns of lubrication oil with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF AMS) in a dedicated engine test that measured the lubrication system vent. The study also tracked the fate of lubrication oil for in-service aircraft where the vented oil vapor interacts with the aircraft combustion exhaust.

Comparing the AMS field measurements of various commercial aircraft engine exhausts with those from the well-controlled monodisperse lubrication oil aerosols generated in the laboratory, it was found that lubrication oil was clearly present in the organic PM emissions from the commercial aircraft engine exhausts. It was associated with emitted soot particles, unlike the purely oil droplets observed at the lubrication system vent.

The contribution from lubrication oil in measured aircraft plumes can range from 5 to 100 %, so they could become the predominant composition in some of the cases.

• Identification of Lubrication Oil in the Particulate Matter Emissions from Engine Exhaust of In-Service Commercial Aircraft,
  Zhenhong Yu, Scott C. Herndon, Luke D. Ziemba, Michael T. Timko, David S. Liscinsky, Bruce E. Anderson, Richard C. Miake-Lye,
  Environ. Sci. Technol. 2012.
  DOI: 10.1021/es301692t