Discrete Element Method Model for Restructuring of Soot Aggregates

EGOR DEMIDOV, Gennady Gor, Alexei Khalizov, New Jersey Institute of Technology

     Abstract Number: 97
     Working Group: Carbonaceous Aerosols

Abstract
Soot is a major component of atmospheric aerosols and it affects climate primarily by scattering and absorbing the sunlight. Morphologically, soot particles are fractal aggregates made of elemental carbon. In the atmosphere, the aggregates acquire coatings by interacting with trace gas chemicals and water vapor, resulting in significant compaction of the aggregates. The addition of coatings and morphological compaction lead to changes in light absorption and scattering, and hence in direct climate forcing by soot aerosol. The mechanism of soot restructuring is not yet fully understood and no models exist to rigorously describe the process of restructuring. Hence, the fractal morphology of soot and its evolution are neglected in atmospheric models, leading to reduced prediction accuracy. To address this deficiency, we develop a discrete element method model to quantitatively simulate restructuring of fractal soot aggregates. In the model, the aggregate is represented as a collection of spheres joined by cohesion and by covalent necks. To describe forces acting in an aggregate, we combine in an open-source code models for elastic bonds, non-bonded frictional contacts, and van der Waals attraction between spheres in the aggregate. The developed model is parametrized based on atomic force microscopy (AFM) force-displacement curves, recorded for soot aggregates unraveled by the AFM cantilever tip. Future work involves adding to the model capillary forces produced by atmospheric condensates and integrating the soot restructuring model into a large-scale atmospheric simulation to quantify the time scale and extent of restructuring occurring under natural conditions.