Impact of Organic Coating on Soot Angular and Spectral Scattering Properties.

In the last two to three decades, many efforts have been made to evaluate the radiative properties of soot in flames. Due to the strong impact of soot on global warming and the aging process of soot particles in the atmosphere, it is necessary to gain a better understanding on how the radiative properties of soot are affected by coating with nonabsorbing organic aerosol compounds. In the present study, the aging process is experimentally mimicked in the laboratory by coating oleic acid onto freshly generated soot particles. The morphological restructuring of soot particles is determined by nonoptical techniques for mobility diameter and effective density and by angular light scattering for gyration radius and fractal dimension. Both approaches give results in good agreement. Moreover, spectrally resolved scattering measurements between 500 and 700 nm have been carried out. The experimental data are in satisfactory agreement with previously published numerical results and enable the validation of a Rayleigh-Debye-Gans theory for coated fractal aggregates (RDG-CFA) that could be integrated in climate models or for the interpretation of scattering based measurements.