Effect of necking and polydispersity in aggregate and primary particle size on the scattering matrix of soot aggregates

Abstract

Morphology of soot aggregates includes complex structures such as necking and polydispersity in aggregate and primary particle size, which have considerable influences on their optical behavior. In this study, a comprehensive analysis of the impact of necking and polydispersity in aggregate and primary particle size is conducted to identify their effects on scattering matrix elements. Typical morphological parameters associated with flame-soot are used to generate aggregate representations via a tunable algorithm based on cluster-cluster aggregation. Necking is implemented via a modified cylindrical connector model and the level-set function model with different coefficients, whereas polydispersity in aggregate and monomer size is introduced assuming log-normal distributions. Scattering properties are calculated via discrete dipole approximation and multi-sphere T-matrix method. Individual impacts of these morphological features on the scattering matrix elements are presented, and the aggregate volume based approach is evaluated for representing the impact of necking. According to the results, the impacts of necking and primary particle polydispersity are similar and dominated by the resultant volume change, whereas that of aggregate polydispersity is more complicated. Accordingly, the aggregate volume based approach performs well in representing the effect of necking on the scattering matrix for the specified cases. The deficiency of the aggregate volume based approach is discussed and a potential way to improve it is proposed.