Spectrally resolved light extinction enhancement of coated soot particles

The aim of the present study is to evaluate experimentally the impact of a non-absorbing coating material on the spectral radiative properties of freshly produced carbonaceous aerosols. Once emitted into the atmosphere, carbonaceous particles are prone to interact with organic chemical compounds to acquire a certain amount of non-absorbing or weakly absorbing coating on their surface. In the present study, oleic acid is used as a surrogate for the coating material and applied to aerosols produced by a miniCAST (soot particles of different chemical and morphological properties) and a spark discharge aerosol generator. A simple analytical model is presented to evaluate the coating thickness. Furthermore, the spectrally resolved extinction cross sections of uncoated and coated particles are determined enabling the evaluation of the mass specific extinction coefficient and the extinction enhancement factor over a wide spectral range (200−1100nm). Influences of the coating thickness and the type of core carbonaceous particles are also discussed.