In-Flight Chemical Composition Observations of Aircraft Emissions using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer

Abstract:

Commercial aircraft are an important source of aerosols to the upper troposphere. The microphysical and chemical properties of these emitted aerosols govern their ability to act as ice nuclei, both in near-field contrails and for cirrus formation downstream. During the ACCESS-II (Alternative Fuel Effects on Contrails and Cruise Emissions) campaign, NASA DC-8 CFM56-2-C1 engine emissions were sampled systematically at a range of cruise-relevant thrust levels and at several altitudes. Sampling was done aboard the NASA HU-25 Falcon aircraft, which was equipped with a suite of aerosol and gas-phase instruments focused on assessing the effects of burning different fuel mixtures on aerosol properties and their associated contrails. Here we present in-flight measurements of particle chemical composition made by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). The AMS was able to sufficiently resolve near-field (within 100m) aircraft emissions plumes. Low-sulfur HEFA (hydro-processed esters and fatty-acids) and JetA fuels yielded particles that contained 11 and 8% sulfate, respectively, compared to 30% sulfate contribution for traditional JetA fuel. Each of the fuels produced organic aerosol with similarly low oxygen content. Lubrication oils, which are not a combustion product but result from leaks in the engine, were likely a dominant fraction of the measured organic mass based on mass-spectral marker analysis. These results are compared to similar engine conditions from ground-based testing.