Tropospheric aerosols play an important role in atmospheric chemistry, Earth's radiative budget and climate. After their generation, aerosol can suffer ageing processes and altering their physicochemical properties. An accurate accounting for these processes requires observations of the aerosol properties on different temporal and spatial scales. The current thesis work is dedicated to: (i) study of physicochemical properties and mixing state of individual particles by means of analytical scanning and transmission electron microscopy for aerosols collected during episodes of elevated aerosol loading; (ii) analysis of the effect of microphysical properties on optical characteristics as measured and retrieved by remote sensing; and (iii) investigation of possible parameterization of aerosol composition and structure in remote sensing algorithms. The work presents observations conducted in northern France and western Africa (Senegal) as part of Labex CaPPA project and SHADOW field campaigns. It includes simultaneous analyses of collected individual particles composition and structure, remote sensing and in situ observations of urban/industrial, Saharan dust and biomass burning particles near the surface and on different altitudes. A series of numerical simulation devoted to an analysis of sensitivity of remote sensing observations to aerosol mixing state is conducted. Insights on possible parameterization of aerosol core-shell structure in retrieval algorithms are finally presented.