Retrieval of aerosol composition directly from satellite and ground-based measurements

Abstract. This study presents a novel methodology for remote monitoring of aerosol composition over large spatial and temporal domains. The concept is realized within the GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm to directly infer aerosol composition from the measured radiances. This approach is different from the conventional methods that use post-processing of the retrieved aerosol optical properties for aerosol typing. The proposed method assumes observed aerosols as mixtures of particles composed of black carbon, brown carbon, absorbing insoluble, non-absorbing insoluble embedded in a soluble host. The algorithm then derives size distribution and the fractions of these components. The complex refractive index of each component is fixed a priori and the complex refractive index of mixture is computed using mixing rules. The approach is first tested with synthetic data and the uncertainties are estimated. Then, it is applied to the real ground-based AERONET and space-borne POLDER/PARASOL observations, known to be sensitive to aerosol complex refractive index. The study presents a first attempt to derive aerosol composition from satellites. The obtained aerosol optical characteristics are highly consistent with the standard products (R of ~ 0.9 for aerosol optical thickness). The approach also presented an ability to separate between aerosol properties in fine and coarse size fractions, in case of POLDER/PARASOL and AERONET. Examples of application to POLDER/PARASOL on the global scale are presented. The obtained spatial and temporal patterns of the aerosol composition agree well with our knowledge on aerosol sources and transport features. Finally, limitations and perspectives are discussed.