AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Dependence of the Optical Properties of Soot Aggregates on Their Morphological Mixing State
OGOCHUKWU ENEKWIZU, Divjyot Singh, Mary McGuinness, Alexei Khalizov, New Jersey Institute of Technology
Abstract Number: 221 Working Group: Aerosol Physics
Abstract Soot nanoparticles, produced from the incomplete combustion of fossil fuels, absorb solar radiation and contribute to climate change by direct radiative forcing. The magnitude of forcing is strongly influenced by the changes in morphology and mixing state of the soot aggregates as they interact with other aerosols during atmospheric transport. However, previous studies on soot optical properties have been largely inconclusive because a systematic examination of the sensitivity of the optical properties of soot to aerosol mixing state has not been performed. For thinly coated soot aggregates, our previous research has shown the existence of two coating distributions (uniform condensation and capillary condensation) governed by the degree of vapor supersaturation of the condensing material. In this study, we investigate the effects of these two distinct mixing states on the light absorption and scattering of coated soot aggregates. We conduct our optical measurements at a wavelength of 530 nm on size-classified soot with different mixing states and morphologies engineered through controlled vapor supersaturation and aging experiments. We compare our results to optical calculations via Discrete Dipole Approximation (DDA) using the morphology and mixing state data derived from our experiments to numerically simulate soot aggregates and apply coating material using an algorithm that describes the aggregate in terms of dipole points. We also contrast our findings against traditionally used RDG and core-shell Mie methods for optical calculations. The outcome of our findings may help address discrepancies in previous studies and improve simulations of the radiative forcing of soot.