Comparison of Aircraft Engine Particle Emissions at Cruise Altitude and at the Ground: Observations from ACCESS and ECLIF-II / ND-MAX

We present measurements of aerosol emissions indices measured in-situ at various cruise altitudes from two different chase plane studies: the 2014 Alternative Fuel Effects on Contrails and Cruise Emissions (ACCESS) study and the 2018 Emission and Climate Impact of Alternative Fuel (ECLIF/ND-MAX) study. ACCESS looked at emissions from the CFM56-2C engines of the NASA DC-8, while ECLIF examined emissions from the IAE V2527 engines of the DLR A320. Aircraft engine emissions can have a disproportionately large climatic impact since they are emitted high in the troposphere and in remote regions with otherwise low aerosol concentrations. This has motivated numerous past ground-based studies focused on quantifying the emissions indices of non-volatile and semi-volatile aerosol species, however, it is unclear the extent to which emissions on the ground translate to emissions at cruise conditions. In-flight emissions were sampled using a large number of aerosol and gas instruments integrated on the chase aircraft, whose sampling inlets were positioned in the DC-8 or A320 exhaust plumes for near field (50-500 m in trail) and far-field (>6 nmi in trail) sampling, respectively. Ground emissions were sampled with a comprehensive suite of instruments housed in a trailer outside of the plume, and emissions were drawn through long sample lines. Previous work has found that the biofuel blend substantially decreases the aerosol number and mass emissions indices, while the gas phase emission indices were similar across fuels, and here we examine the variation of the aerosol emissions with altitude and the connection to the ground test measurements.