Effect of size distribution of monomers on the radiometric properties of micro/nano aggregates for different materials

Abstract

The radiometric properties of micro/nano aggregates formed by nano monomers are essential in many scientific disciplines. The aggregate model of single-sized monomers is often used to calculate the radiometric properties of micro/nano aggregates. However, the size distribution of monomers commonly exists in most of the actual aggregates and critically influences the radiometric properties. However, the influencing mechanism remains unclear. This paper discusses the influence of size distribution of monomers on the radiometric properties of micro/nano aggregates formed by nano monomers. The monomers of the aggregates have lognormal size distributions. Diffusion-limited aggregation method is used to generate the structure of aggregate, and multi-sphere T-matrix method is used to calculate the extinction efficiency, absorption efficiency, scattering efficiency, and phase function of aggregate for three representative materials and different size distributions of monomers. The influence of the geometric standard deviation of lognormal distribution and monomer number on the radiometric properties of aggregate for the three representative materials is investigated, and the mechanism is explained. Results show that the extinction and absorption efficiencies of gold aggregate decrease as the geometric standard deviation increases with the same average monomer size due to the coupling particle–plasma mode oscillation alternating between super-radiation and sub-radiation. Meanwhile, the extinction efficiency of ice and black carbon aggregates increases due to the increase in large monomers as the geometric standard deviation increases from 0 to 0.5. The size distribution of monomers mainly affects the distribution of back-scattering in comparison with forward-scattering. For extinction and scattering efficiencies, the aggregate model with size distribution of monomers and the aggregate model with single-sized monomers are close for gold aggregate; the former model is larger than the latter model for black carbon and ice aggregates. For absorption efficiency, the former model is lower for gold aggregate and higher for black carbon aggregate.