Photo-transformation of particles of atmospheric interest and influence on their hygroscopic properties. A levitation technique coupled to the Raman microscope study

Doctorante: Samantha Seng

In the frame of global warming, confirmed by the Intergovernmental Panel on Climate Change (IPCC), the role of aerosol particles on the climate change is still poorly understood (IPCC, 2007). Hygroscopic properties of the particles play a major role on their climatic impact. Size, chemical composition and mixing state of particles are the parameters that govern their ability to adsorb water in the atmosphere.  Moreover, during their stay in the atmosphere, particles undergo complex physicochemical mechanisms induced not only by the presence of humidity, pollutant gases, other particles or gaseous chemical species but also by solar radiation. These physicochemical transformations taking place at the individual particle scale involve, over time, a change of their size, their chemical composition and their mixing state and finally their hygroscopic property. This thesis project aims to study (i) the photo-transformation of individual particles of complex composition, and (ii) the influence of the physicochemical changes induced by light on the hygroscopic properties of the particles. Studies will be performed in the laboratory using an acoustic levitation device coupled to the Raman microscope that has been recently developed at LASIR. This device dedicated to the study of individual particles of atmospheric interest is unique in France which brings an added value to the thesis project. Furthermore, the results of these experiences will be compared with the mechanisms and products observed for the organic molecules isolated in matrices that will be carried out in the framework of a collaborative project with the University of La Plata, Argentina (project ECOS-SUD obtained for 2014 to 2016). These studies will provide a basis for understanding the photochemistry and the catalytic role of the atmospheric particles, as well as the physicochemical parameters governing the hygroscopic properties of aerosols in the atmosphere. The project is in the research activities of LABEX CaPPA (ANR-11-LBX-0005-01) which LASIR is involved.

Director: Sophie Sobanska (LASIR)
Co-responsible: Yéni Tobon (LASIR)

Laboratory: LASIR

Financing: Université Lille 1 / Labex CAPPA