A shape model of internally mixed soot particles derived from artificial surface tension
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.