Study of atmospheric visibility pertaining to soot scavenging by sulfate droplets

The effect of soot scavenging by sulfate aerosols on visibility in the atmosphere is investigated through analytical calculations of the light extinction coefficient of sulfate-soot mixtures, both internal and external. Soot grains are modeled as porous carbon spheres, whereas sulfate aerosols are modeled as spherical, aqueous, sulfuric acid droplets. A soot grain is either surrounded by an eccentric, spherical, sulfate shell (internal mixture), or it is in contact with a sulfate droplet (external mixture). The number density of the polluting particles is determined through the mass concentration of elemental carbon and sulfuric acid in the atmosphere. The extinction cross section of composite sulfate-soot particles is obtained by use of existing analytical, indirect-mode matching solutions to the problem of electromagnetic-wave scattering by a sphere with an eccentric spherical inclusion or by a cluster of spheres. Effects on visibility of the size, orientation and mass concentration of the polluting particles are investigated for several wavelengths across the visible band.