Nanoscale characterization of aircraft soot: A high-resolution transmission electron microscopy, Raman spectroscopy, X-ray photoelectron and near-edge X-ray absorption spectroscopy study

Abstract

Particulate emissions from jet aircraft are a significant source of carbonaceous particles in the troposphere and lower stratosphere. Determining their physical structure and chemistry is relevant to assess their impact upon contrail formation, the radiative balance of the atmosphere, and human health. In this report, aircraft soot particles emitted by a recent turbofan engine, the PowerJet SaM146-1S17, fueled with Jet A-1, have been investigated with high-resolution transmission electron microscopy-in imaging, selected area electron diffraction mode, and energy dispersive X-ray spectroscopy-, Raman spectroscopy, X-ray photoelectron spectroscopy and near-edge X-ray absorption spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of soot primary particles. Independently of the engine operating regimes, these particles are mainly composed of graphitic layers arranged in onion-like, turbostratic structures. They are poorly oxidized, with a slight enhancement of the oxidation rate at the very surface. The soot's surface also presents a high concentration of unsaturated organic hydrocarbons and structural defects. These results allow a better description of aircraft soot at the atomic level, and may account for a better understanding of ice nucleation in aircraft contrails formation.

Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy

“…Thus, we can assign the peak A to C=O groups, and the peak B to aromatic carbonyl and/or carboxyl groups. These interpretations confirm previous observations performed on soot, oxidized nanodiamonds and other organic moieties [54,78,93].…”

“…A linear background was subtracted and heights H D and HG were measured without any fitting to prevent from ambiguousness due to a model-dependent fitting procedure [18,19]. This last choice was done because a debate still exists in the literature concerning how to fit properly amorphous carbon Raman spectra [1,30,78,79]. H D was therefore measured at its apparent maximum, except when the D band maximum was not well enough defined.…”

“…fullerene-like) [78,[92][93][94][95][96][97]. For instance, aromatic C-OH group will give rises to transitions to π* states in the energy range 285.8-286.4 eV, C=O group to transitions to π* states in the energy range 286.5-288.3 eV, C-H group to transitions to σ* states in the energy range 287.6-288.2 eV and aromatic carbonyl and carboxyl groups to transitions to π* states in the energy range 287-288.5 eV [54,78,[92][93][94]96].…”

First in-flight synchrotron X-ray absorption and photoemission study of carbon soot nanoparticles

“…Achieving surface sensitivity is one of the main features of X-ray Photoelectron Spectroscopy (XPS), a technique widely used for studying the chemical composition of solid materials. XPS has been applied over the last two decades on soot particles1011, along with Near Edge X-ray Absorption Fine Structure (NEXAFS)121314, a surface-sensitive technique that uses the photoelectric effect for detection purposes. These methods have also been successfully used in the field of water/soot interactions1516, atmospheric ageing171819 or high temperature oxidation2021.…”

Nanoscale Characteristics and Reactivity of Nascent Soot from n-Heptane/2,5-Dimethylfuran Inverse Diffusion Flames with/without Magnetic Fields

“…The core area was filled with amorphous structures which had very little or no crystallinity with relatively strong oxidation activity. The core was surrounded by the orderly bordered lamellae as the fullerenic nanostructure which was similar to the fingerprint structure and partly carbonized yet [75][76][77][78]. It could be noted that the oxidation activity of soot depended on comprehensive consideration of the area size of the soot particle core and the thickness of the shell around.…”