AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Optical Properties and Q-space Study of Fractal-like Soot Aggregates from Coal Combustion Based on 3-D Electron Tomographic Reconstruction
CHENCHONG ZHANG, William Heinson, Jingkun Jiang, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 312 Working Group: Aerosol Physics
Abstract Soot aggregates constitute the major fraction of particulate matter emitted from anthropogenic sources. Freshly emitted soot particles have complex fractal-like morphologies that can significantly influence the particles’ microphysical and optical properties, thereby impacting the earth’s radiative forcing.
Diffusion limited cluster-cluster aggregation (DLCA) has been considered as a high-fidelity simulation of soot aggregates generation process. The most optical and morphological studies of fractal-like soot particles are based on DLCA aggregates. However, there are few studies accurately parameterize soot aggregates’ morphology and quantitatively evaluating their spectral radiative properties based on their real shape. In this study, we detect the detailed three-dimensional (3-D) structure of aggregates by using electron tomography technique. To compensate for ‘the missing wedge’, an inherent defect of limited-angle projection images, we incorporate total variation minimization in addition to traditional weighted back projection approach. The reconstructed soot particle models precisely capture detailed morphological information about the aggregates, for example, the exact shapes of primary particles and the necking between monomers. Next, we calculate the Fourier transform of the density auto-correlation function of the voxels (also known as the particle structure factor) to accurately characterize the fractal morphology of the reconstructed particles. Our goal is to validate the conventional view that combustion-generated fractal aggregates formed via DLCA, have a universal mass fractal dimension of 1.8. Finally, we conclude this work by applying the discrete-dipole approximation on reconstructed aggregate models to derive their spectral optical properties, including scattering and absorption cross-sections, and asymmetry and Stokes parameters.