Carbonaceous soot particles are formed during the incomplete combustion of fossil fuels, biofuels and biomass burning and are considered to contribute to a significant part of aerosol emission, especially in polluted areas. Soot particles are known to contain the light-absorbing carbon fractions of Black Carbon (BC) and Brown Carbon (BrC) making them a key species when trying to understand and estimate the interaction between aerosols and atmospheric radiation, i.e. the direct radiative effect (DRE). Current estimations of the DRE of soot and its BC and BrC components remain uncertain due to the difficulties in representing their microphysical and spectral optical properties in models. In particular, gaps persist in describing the variability of the soot optical properties at the source, due to different combustion conditions, and their change during atmospheric lifetime, due to mixing with different aerosol components. Further, differences between laboratory observations and field measurements remain and are not understood.

The present work aims to provide new measurements and descriptions of the physical, chemical, and spectral optical properties of BC- and BrC-containing soot aerosol in order to improve its representation in models. The focus of this work is set on advancing the understanding and description of the variability of the soot properties 1) at generation, from changing combustion conditions, and 2) during atmospheric ageing, in particular, due to the internal mixing with inorganic and organic compounds forming coating at the soot surface. To provide a mechanistic study of soot aerosol properties a coherent set of experiments was set up using the large atmospheric simulation chamber CESAM (French acronym for Multiphase Atmospheric Experimental Simulation Chamber) and a controllable propane-based soot generator.

The experiments were used to determine key optical parameters used in modelling and remote sensing applications like the mass absorption, extinction and scattering cross-section (MAC, MEC, MSC), the single scattering albedo (SSA), and the complex refractive index (CRI). The varying properties of the soot from different combustion conditions allowed the investigation and support of a generalized relationship between the MAC and the particle chemical composition for fresh-emitted particles. Optical calculations based on two descriptions of the particle’s morphology were performed to determine the soot’s CRI and discuss the usability and pertinence of data from different shape representations assumptions.

Soot aerosols were subjected to different simulated atmospheric ageing processes to determine the effects of ageing on their absorbing capacity and physico-chemical properties. Especially, the formation of a coating and the enhancement of the absorption due to this internal mixing were studied using two precursors and coating processes. This enabled the investigation of the relationship between absorption enhancement, particle processing, and coating thickness, relevant across the soot lifecycle.

Defence will be conducted in English.

Lieu
Auditorium MSE, UPEC, Créteil

Visio
https://cnrs.zoom.us/j/95032189038?pwd=D16fNyWQR4QDoQIqozqRfV7yDpPIyw.1

• Romain CEOLATO – Rapporteur
• Athanasios NENES – Rapporteur
• Cyrielle DENJEAN – Examinatrice
• Daniela MELONI – Examinatrice
• Denis PETITPREZ – Examinateur
• Bénédicte PICQUET-VARRAULT – Examinatrice
• Jean-François DOUSSIN – Directeur de thèse
• Claudia DI BIAGIO – Co-encadrant de thèse
• Martin GYSEL-BEER – Invité