Thesis of Philippe Lesueur

Defense of thesis Philippe Lesueur - laboratory LOA

Abstract :

Atmospheric aerosols influence the Earth’s radiative budget in the surface-atmosphere system, affect the cloud formation and microphysics, air quality and visibility, hence have an important impact on climate, environment and even socio-economical processes. Remote sensing methods of aerosol observations can provide information on optical and microphysical properties on a wide scale in near real-time, but also on global, regional or local climatology.
Composition and mixing state of aerosol is crucial for understanding and evaluation of aerosol interactions with climate and environment. However, such characterisation by remote sensing is an extremely challenging task. In addition, aerosol can suffer from rapid and important structural modifications during their lifetime in the atmosphere, for which monitoring can be difficult. One of those modifications is water uptake and the creation of coating on particles. This aerosol coating can significantly change their radiative impact, but also their ability to interact with other substances in the atmosphere and serve as cloud condensation nuclei.
This thesis work is focused on the problematic of the aerosol coating by a liquid material and is dedicated to : (i) study the impact of particles coating on scattering properties using numerical simulation of a core/shell model by the Mie theory for layered spheres; (ii) calculation and implementation of pre-computed tables of a core/shell model for an inversion algorithm (GRASP); (iii) tuning and testing the sensitivity to core/shell aerosol retrieval using synthetic measurements; (iv) numerical inversion of ground-based sunphotometric measurements by the AERONET global network using the newly suggested aerosol model; and (v) studying its impact on aerosol retrievals and coherence of the retrieved core/shell aerosol fraction with the on-site conditions.
This work thus presents results of theoretical influence of aerosol coating on light scattering properties, a newly suggested parametrisation of a remote sensing algorithm, analysis of the regime of the algorithm applicably and illustration for the performance using several measurement sites that represent urban, desert or mixed aerosol types.

Keywords : Aerosol, aerosol water uptake, aerosol inhomogeneity, photometer, AERONET network, remote sensing