A Multiscale Model for Restructuring of Atmospheric Soot Particles

This project is focused on the development of a multiscale model to predict the evolution of soot particles during atmospheric processing. The nature of soot particles can change after emission through restructuring when they come in contact with trace gas chemicals and water vapor in the atmosphere. Advances in modeling the atmospheric processing of soot will help to reduce uncertainties in the atmospheric lifetime of soot and also will improve the assessment of the impacts of soot on air quality, human health, and climate. This effort will address outstanding questions on the origin and magnitude of changes to soot aggregates, including: (1) the stress induced by condensate located in junctions between monomers and monomer branches, and (2) the forces holding together the individual monomers. A Discrete Element Method (DEM) model will be developed in which soot restructuring is driven by stresses from a growing or shrinking layer of condensate and resisted by necks between monomers. The DEM model will be parameterized using atomic-level simulations and lab experiments. Experiments will be conducted using mass-mobility measurements, electron microscopy, and atomic force microscopy to obtain the required neck parameters (number and size distribution, strength, and atomic structure). Two major soot aging mechanisms will be considered: the condensation of trace-gas chemicals to form coatings, and the subsequent cloud processing of coated soot particles. This project will provide interdisciplinary training for graduate and undergraduate students and young researchers in a rich interdisciplinary environment. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.