10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Effects of Uneven Coating on the Absorption Enhancement of Soot Aggregates
WILLIAM HEINSON, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 439 Working Group: Carbonaceous Aerosol
Abstract Soot Aggregates (SAs) in the atmosphere significantly influence the earth’s radiation balance, visibility, and public health. They are formed from high-temperature, incomplete combustion of fossil fuels and biomass burning via diffusion limited cluster-cluster aggregation (DLCA) of spherical monomers. SAs can contain a significant amount of non-refractory compounds coated on to its surface which may enhance the SA’s natural light absorptive properties through “lensing” effects. Depending on the strength of the lensing effect, the absorption enhancement can be up to a factor of 3. We studied how the wetting of the coating material onto the SA’s affects the absorption enhancement. A Monte-Carlo method was employed to simulate the affinity of the coating materials to wet the SAs. The coated SAs’ light absorption properties were then calculated using a discrete dipole approximation (DDA) algorithm. In many climate models, SAs are approximated by an equivalent-mass core-shell spherical model due to the ease of calculating optical properties using Lorentz-Mie theory. Keeping this in mind, we calculated the optical properties of core-shell spheres equivalent in mass to our coated SAs. Comparisons of the core-shell spheres with the coated aggregates showed that the mass absorption cross-sections (MAC) were significantly underestimated in the core-shell approximation when the coating uniformly wetted the SAs. When the coating was not evenly applied to the SAs, the enhancement could be significantly reduced.