AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Predicting the Phase State of Atmospherically Relevant Aerosols and Its Impact on Multiphase Chemistry in a Regional-scale Atmospheric Model
QUAZI RASOOL, Ryan Schmedding, Yue Zhang, Havala Pye, Haofei Zhang, Yuzhi Chen, Jason Surratt, William Vizuete, University of North Carolina at Chapel Hill
Abstract Number: 451 Working Group: Aerosol Chemistry
Abstract Accurate prediction of the phase state of secondary organic aerosols (SOA) is critical to quantify the impact on climate and air quality. Phase separation in SOA can create a highly viscous organic shell that surrounds an inorganic core, which can decrease both the partitioning of the semi-volatile species and the extent of acid-catalyzed heterogeneous reactions. Studies have showed that aerosols phase separate over 70% of the time at a rural site in the Southeast US by using observed compositions with thermodynamic models to predict organic and inorganic constituents as well as aerosol water content. However, such phase separation processes have not been fully incorporated into atmospheric models. This work developed algorithms for SOA phase separation that were included in a regional-scale atmospheric model (CMAQ). These new algorithms determine phase state by accounting for the mechanistic interactions between products of oxidizing precursor molecules, particle morphology, meteorology, and the aerosol water content. Our approach also estimates the glass transition temperatures (Tg) of SOA components by accounting the variability in composition of different organic compounds, aerosol water, and the atomic oxygen-to-carbon (O:C) ratio. When Tg determines a liquid state, we also included algorithms to determine whether there is Liquid-Liquid Phase Separation (LLPS), as recent literatures show that Tg provides a more accurate indication of phase separation that correlates well with the viscosity of SOA. Multiphase chemistry of isoprene-derived epoxydiols is one of the major sources of SOA in the troposphere. Our implementation is a first to focus on this critical pathway to estimate the impact of SOA phase separation on multiphase chemical reactions. To sum up, this work enables predictions of phase separation frequencies across varied conditions and subsequently examines the influence on isoprene-derived SOA phase separation due to aerosol viscosity, morphology, and phase state.