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Discussion papers
https://doi.org/10.5194/acp-2018-1171
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1171
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Dec 2018

Research article | 04 Dec 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Chemical composition, optical properties and radiative forcing efficiency of nascent particulate matter emitted by an aircraft turbofan burning conventional and alternative fuels

Miriam Elser1,2, Benjamin T. Brem1, Lukas Durdina1, David Schönenberger1, Frithjof Siegerist3, Andrea Fischer4, and Jing Wang1,2 Miriam Elser et al.
  • 1Laboratory for Advanced Analytical Technologies, Empa, Dübendorf, 8600, Switzerland
  • 2Institute of Environmental Engineering, ETH, Zürich, 8049, Switzerland
  • 3SR Technics AG, Zurich-Airport, 8058, Switzerland
  • 4Air pollution/Environmental Technology, Empa, Dübendorf, 8600, Switzerland

Abstract. Aircraft engines are a unique source of carbonaceous aerosols in the upper troposphere. There, these particles can more efficiently interact with solar radiation than at ground. Due to the lack of measurement data, the radiative forcing from aircraft particulate emissions remains uncertain. To better estimate the global radiative effects of aircraft exhaust aerosol, its optical properties need to be comprehensively characterized. In this work we present the link between the chemical composition and the optical properties of the particulate matter (PM) measured at the engine exit plane of a CFM56-7B turbofan. The measurements covered a wide range of power settings (thrust), ranging from ground idle to take-off, using four different fuel blends of conventional Jet A-1 and Hydro-processed Ester and Fatty Acids (HEFA) biofuel. At the two measurement wavelengths (532 and 870nm) and for all tested fuels, the absorption and scattering coefficients increased with thrust, as did the PM mass. The separation of elemental carbon (EC) and organic carbon (OC) revealed a significant mass fraction of OC (up to 90%) at low thrust levels, while EC mass dominated at medium and high thrust. The use of HEFA blends induced a significant decrease in the PM mass and the optical coefficients at all thrust levels. The HEFA effect was highest at low thrust levels, where the EC mass was reduced by up to 50–60%. The variability in the chemical composition of the particles was the main reason for the strong thrust dependency of the single scattering albedo (SSA), which followed the same trend as the OC fraction. Mass absorption coefficients (MAC) were determined from the correlations between aerosol light absorption and EC mass concentration. The obtained MAC values (MAC532=7.5±0.3m2g−1 and MAC870=5.2±0.9m2g−1) are in excellent agreement with previous literature values of absorption cross section for freshly generated soot. The Simple Forcing Efficiency (SFE) was used to evaluate the direct radiative effect of aircraft particulate emissions for various ground surfaces. The results indicate that aircraft PM emissions over highly reflective surfaces like snow or ice have a substantial warming effect. The use of the HEFA fuel blends decreased PM emissions, but no changes where observed in terms of EC/OC composition, optical properties and forcing per mass emitted.

Miriam Elser et al.
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Miriam Elser et al.
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Empairex 1: Optical properties data archive M. Elser, B. T. Brem, L. Durdina, D. Schönenberger, F. Siegerist, A. Fischer, and J. Wang https://doi.org/10.5281/zenodo.1918161

Miriam Elser et al.
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Short summary
This work presents the link between the chemical composition and the optical properties of the aerosol emissions of an aircraft turbofan using conventional and alternative fuels. A high organic carbon fraction at low thrusts is linked to high single scattering albedos. The optical properties at cruise conditions are used to evaluate the radiative forcing efficiency of aircraft aerosol emissions, which have a substantial warming effect when emitted over highly reflective surfaces such as snow.
This work presents the link between the chemical composition and the optical properties of the...
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