Innovative aerosol hygroscopic growth study from Mie-Raman-Fluorescence lidar and Microwave Radiometer synergy

Abstract. This study focuses on the characterization of aerosol hygroscopicity using remote sensing techniques. We employ a Mie-Raman-Fluorescence lidar (LILAS), developed at the ATOLL platform, Laboratoire d’Optique Atmosphérique, Lille, France, in combination with the RPG-HATPRO G5 microwave radiometer to enable continuous aerosol and water vapor monitoring. We identify hygroscopic growth cases when an aerosol layer exhibits an increase in both aerosol backscattering coefficient and relative humidity. By examining the aerosol layer type, determined through a clustering method, the fluorescence backscattering coefficient, which remains unaffected by the presence of water vapor, and the absolute humidity, we verify the homogeneity of the aerosol layer. Consequently, the change in the backscattering coefficient is solely attributed to water uptake. The Hänel theory is employed to describe the evolution of the backscattering coefficient with relative humidity and introduces a hygroscopic coefficient, γ, which depends on the aerosol type. Case studies conducted on July 29 and March 9, 2021 examine respectively an urban and a smoke aerosol layer. For the urban case, γ is estimated as 0.47±0.03 at 532 nm; as for the smoke case, the estimation of γ is 0.5±0.3. These values align with those reported in the literature for urban and smoke particles. Our findings highlight the efficiency of the Mie-Raman-Fluorescence lidar and Microwave radiometer synergy in characterizing aerosol hygroscopicity. The results contribute to advance our understanding of atmospheric processes, aerosol-cloud interactions, and climate modeling.