Exploring the Effects of Chemical Composition on Viscosity of Secondary Organic Aerosol from n-alkanes Oxidation

TOMMASO GALEAZZO, Bernard Aumont, Manabu Shiraiwa, University of California, Irvine

     Abstract Number: 138
     Working Group: Aerosol Chemistry

Abstract
Secondary organic aerosols (SOA) are major components of atmospheric particulate matter, affecting climate and air quality. Mounting evidence exists that SOA can adopt a viscous state, which may impact formation and partitioning of SOA. Viscosity of SOA can be estimated from the glass transition temperature (T_g) of constituting species and their concentrations in SOA. Recently we developed the tgBoost model for predicting T_g of organic molecules by using machine learning algorithms and molecular embeddings. tgBoost has a mean absolute error of 18.3 K, and it predicts T_g considering molecular functionality and structure, hence distinguishing between compositional isomers.

We simulated gas-phase oxidation of n-alkanes under high NO_x conditions and subsequent SOA formation using the GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) model. We implemented tgBoost into GECKO-A and explored the impacts of chemical composition on viscosity. The simulated SOA yields, masses and viscosities were compared to chamber experiments to evaluate the role and impacts of gas-phase chemistry and phase state on SOA formation. We also explored the molecular composition of SOA and highlighted the role of functionality in simulating SOA viscosity.