AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Mass Absorption Cross Section and its Enhancement Factor for Internally Mixed Black Carbon Aggregates with varying Fractal Dimension
PAYTON BEELER, William Heinson, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 488 Working Group: Aerosol Physics
Abstract Mass absorption cross section (MAC) of black carbon (BC) aggregates is an important parameter in many climate models. An underestimation of MAC of BC aggregates can lead to errors in the estimation of radiative forcing due to BC in the atmosphere. BC aggregates are produced by incomplete combustion of biomass and fossil fuels. Aggregates of BC monomers are formed through diffusion-limited cluster aggregation (DLCA) of BC monomers. Organic compounds can then coat the surface of the BC aggregates, which alter the aggregate’s fractal morphology via capillary and surface tension forces. This leads to an increase in the fractal dimension of emitted BC aggregates as the amount of coating increases. This study generates aggregates using three aggregation mechanisms; DLCA (Df = 1.8), percolation (Df = 2.5), and face-centered cubic stacking (Df = 3). The aggregates are then coated with refractory (absorbing) and non-refractory (non-absorbing) organics, and their optical properties are calculated using the Amsterdam discrete dipole approximation (ADDA). The MAC values of the coated aggregates are next calculated and compared against uncoated aggregates for determination of MAC enhancement factors across a large size range.