AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Predicting the Glass Transition Temperature and Viscosity of Secondary Organic Aerosols Using Molecular Composition
WING-SY WONG DERIEUX, Ying Li, Mallory Hinks, Peng Lin, Julia Laskin, Alexander Laskin, Sergey Nizkorodov, Manabu Shiraiwa, University of California, Irvine
Abstract Number: 561 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA) account for a large fraction of submicron particles in the atmosphere. Traditionally, SOA particles have been assumed to be homogeneous and well-mixed liquids. Recent laboratory experiments as well as atmospheric measurements, however, have demonstrated that they can occur in amorphous solid or semi-solid phase states depending on chemical composition, relative humidity and temperature. The particle phase state is crucial for various atmospheric gas–particle interactions, including SOA formation and partitioning, heterogeneous and multiphase reactions and ice nucleation. It is important to know the SOA phase state in multicomponent atmospheric particles for better quantification of aerosol effects on climate and air quality. The glass transition temperature (Tg) characterizes the non-equilibrium phase change from a glassy solid state to a more pliable semi-solid state as the temperature increases. Recently, we have developed a method to estimate Tg of SOA oxidation products using their elemental composition. In this study, kinetic fragility values from literature have been compiled and analyzed to identify trends related to molar mass and O:C ratio. As molar mass increases, we find that the fragility strength parameter (D) approaches a lower limit of ~10 (+/- 1.7). A weak correlation between fragility and molecular O:C ratio is observed. Using the estimated Tg and the fragility parameter, we have predicted viscosity of α-pinene and isoprene SOA as a function of RH, which matches with experimental measurements well. The effect of varying Tg, fragility, hygroscopicity and Gordon-Taylor constant on viscosity is explored. We also have estimated Tg and viscosity of toluene SOA using the elemental composition measured by high-resolution mass spectrometry.