Analysis of in situ and remote sensing vertical measurements of aerosol properties in the Rhône valley

Aerosols have a significant impact on Earth’s climate and human health. The spatial and temporal distribution of aerosols is very heterogeneous and therefore difficult to constrain in atmospheric models. In situ measurements are very useful to shed light on aerosols’ distribution and processes. However, many questions regarding aerosols remain open. The vertical distribution of aerosol particles represents key information to understand their effect on climate and health, however vertical in situ observations of aerosol characteristics remain scarce. Ground measurements are not necessarily representative of concentrations found at higher altitudes: the stability of the air parcels can vary with the altitude, causing some mixing or accumulation of particles at certain heights. In Alpine valleys, with complex topography and particular wind regimes, the vertical dispersion of aerosol particles can follow very different patterns. In high stability cases, surface accumulation of particulate matter can have detrimental effects on human health caused by high ground concentration. To address the need to better constrain the vertical distribution of aerosols in Alpine valleys, a measurement campaign took place in Brigerbad (Valais, Switzerland) in fall 2021, with a ground measurement station, a Doppler Lidar and a tethered balloon-based aerosol in situ measurement system. The campaign totalized 26 flights at different times of the day. Trace gases, aerosol characteristics, and meteorological parameters were measured at ground level and above. Several numerical methods have been developed and used to analyze the temperature profiles, aerosol distribution and Lidar vertical data. Multiple temperature derivation methods have been tested and compared. A temperature inversion layer (IL) method has been adapted and implemented, while a simple atmospheric boundary layer height (ABLH) detection method has been applied. The aim of the thesis is twofold: better understand the relationships between the thermodynamic structure of the atmosphere and (1) The aerosol concentration and (2) The aerosol size distribution. As temperature inversion layers (ILs) inhibit any vertical movement, they tend to prevent pollutants’ dilution and favor their accumulation below. On the contrary, an unstable atmosphere, driven by convection, mixes the aerosols vertically and therefore reduces the ground concentration. Here, no link could be found between the potential temperature gradient and the aerosol concentration anomaly. There is however a significant link between the potential temperature anomaly and the aerosol concentration anomaly. In general, the aerosol concentration tends to be high at the bottom of surface inversion. Health issues caused by increased particulate matter (PM) concentration are therefore mostly determined by ILs. Future research could explore the relationship between aerosol concentration and potential temperature, as well as the determining factors in the for