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Title: Chemical composition and radiative properties of nascent particulate matter emitted by an aircraft turbofan burning conventional and alternative fuels
Authors : Elser, Miriam
Brem, Benjamin Tobias
Durdina, Lukas
Schönenberger, David
Siegerist, Frithjof
Fischer, Andrea
Wang, Jing
Published in : Atmospheric Chemistry and Physics
Volume(Issue) : 19
Pages : 6809
Pages to: 6820
Publisher / Ed. Institution : European Geosciences Union
Issue Date: 2019
License (according to publishing contract) : CC BY 4.0: Attribution 4.0 International
Language : English
Subjects : Aircraft emissions; Aviation; Black carbon; Alternative fuel
Subject (DDC) : 540: Chemistry
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 exhaust aerosol 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 870 nm) and for all tested fuels, the absorption and scattering coefficients increased with thrust, as did the PM mass. The analysis 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 fraction of OC to total carbon (TC). Mass absorption coefficients (MACs) were determined from the correlations between aerosol light absorption and EC mass concentration. The obtained MAC values (MAC532=7.5±0.3 m2 g−1 and MAC870=5.2±0.9 m2 g−1) are in excellent agreement with previous literature values of absorption cross section for freshly generated soot. While the MAC values were found to be independent of the thrust level and fuel type, the mass scattering coefficients (MSCs) significantly varied with thrust. For cruise conditions we obtained MSC532=4.5±0.4 m2 g−1 and MSC870=0.54±0.04 m2 g−1, which fall within the higher end of MSCs measured for fresh biomass smoke. However, the latter comparison is limited by the strong dependency of MSC on the particles' size, morphology and chemical composition. The use of the HEFA fuel blends significantly decreased PM emissions, but no changes were observed in terms of EC∕OC composition and radiative properties.
Departement: School of Engineering
Organisational Unit: Centre for Aviation (ZAV)
Publication type: Contribution to magazine or newspaper
DOI : 10.21256/zhaw-3246
ISSN: 1680-7324
Published as part of the ZHAW project : AGEAIR: Vermessung der Effekte des Mantelstromtriebwerkverschleisses auf die Schadstoffzusammensetzung
Appears in Collections:Publikationen School of Engineering

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