Abstract
Abstract. To retrieve the physical properties of aerosols from multi-channel ground-based and satellite measurements, we developed a shape model of coated soot particles and created a dataset of their optical properties. Bare soot particles were assumed to have an aggregate shape, and two types of aggregates with different size–shape dependences were modeled using a polyhedral Voronoi structure. To simulate the detailed shape properties of mixtures of soot aggregates and adhered water-soluble substances, we propose a simple model of surface tension derived from the artificial surface potential. The light-scattering properties of the modeled particles with different volume fractions of water-soluble material were calculated using the finite-difference time-domain method and discrete-dipole approximation. The results of the single-scattering albedo and asymmetry factors were compared to those of conventional internally mixed spheres (i.e., effective medium spheres based on the Maxwell-Garnett approximation and simple core-shell spheres). In addition, the lidar backscattering properties (i.e., lidar ratios and linear depolarization ratios) of the modeled soot particles were investigated. For internally mixed soot particles, the lidar backscattering properties were sensitive to the shape of the soot particles and the volume mixing ratio of the assumed water-soluble components. However, the average optical properties of biomass smoke, which have been reported from in situ field and laboratory measurements, were difficult to explain based on the individually modeled particle. Nonetheless, our shape model and its calculated optical properties are expected to be useful as an alternative model for biomass smoke particles in advanced remote sensing via multi-channel radiometer and lidar measurements.
Highlights
During the atmosphere aging process of emitted combustion products, soot particles tend to become hydrophilic and form mixtures with weakly light-absorbing materials (Mikhailov et al, 2006; Adachi et al, 2007; Moteki and Kondo, 2007; Shiraiwa et al, 2007, 2010; Adachi and Buseck, 2008)
The internally mixed soot model was created for different values of the volume ratio Vr = Vws/Vsoot, where Vws and Vsoot are the volumes of the WS and soot materials, respectively
For satellite- and ground-based remote-sensing analysis applications, we developed a shape model of internally mixed soot particles and calculated the optical properties of particles at visible and near-infrared wavelengths
Summary
During the atmosphere aging process of emitted combustion products, soot particles tend to become hydrophilic and form mixtures with weakly light-absorbing materials (Mikhailov et al, 2006; Adachi et al, 2007; Moteki and Kondo, 2007; Shiraiwa et al, 2007, 2010; Adachi and Buseck, 2008). Because of significant enhancements in light absorption and scattering, it has been suggested that soot particles in a mixing state are the second most important contributor to global warming after carbon dioxide (Jacobson, 2001; Ramanathan et al, 2008). Many shape models have been proposed for internally mixed soot particles and their light-scattering properties using the discrete-dipole approximation (DDA) and T-matrix methods (Adachi et al, 2010; Scarnato et al, 2013; Cheng et al, 2014; Dong et al, 2015; Liu et al, 2016; Mishchenko et al, 2016; Moteki, 2016; Wu et al, 2016, 2017; Kahnert, 2017; Zhang et al, 2017; Luo et al, 2018). H. Ishimoto et al.: Mixed soot particle model or morphology and light-scattering properties is not well defined. The numerical results of the light-scattering properties of the modeled particles at visible and near-infrared wavelengths are discussed
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