Scattering and absorption cross sections of compounded spheres II Calculations for external aggregation

The cross section for total scattering by a cluster of spheres derived previously [ J. Opt. Soc. Am. A11, 3251 ( 1994)] is applied to a study of the effects of scavenging and aggregation on the specific absorption of carbon. Results are presented for absorption cross sections of sulfate haze elements and cloud droplets with small carbon grains (spheres) attached to their surfaces. Soot typically occurs as aggregates of carbonaceous spherules. In order to address the validity of certain assumptions that are made in the analysis of such structures by fractal optics, comparisons are provided among the absorption cross sections of free carbon, linear chains, and tightly clumped carbon spheres. Polarization- and orientation-dependent cross sections of composite and aggregate particles are profiled, and orientation-averaged cross sections are tabulated.