10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Connecting Phase Separations in Ambient Secondary Organic Aerosol and Ammonium Sulfate Particles to Relative Humidity and Temperature
ANDREW AULT, Amy Bondy, Sydney Niles, Peter Peterson, Little Josie, Rashad Pace, Ryan Moffet, Rachel O'Brien, Bingbing Wang, Alexander Laskin, University of Michigan
Abstract Number: 1122 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) is a ubiquitous component of submicron ambient aerosol, but its formation mechanisms and the connection between chemical composition and physical properties are not well understood. In recent years, phase has been shown to range from to solid to semi-solid to liquid for ambient particles via bounce measurements, while modeling has predicted that organics should be solid or semi-solid over land. Morphology (e.g. core-shell) of SOA has been primarily studied to the laboratory, where studies have shown morphologies ranging from well-mixed liquid particles to core shell or more complex morphologies as a function of relative humidity (RH) and temperature. However, direct evidence of non-liquid phases and phase separation in individual, ambient particles is limited. Herein, we show that internally mixed SOA and inorganic salt (e.g. ammonium sulfate) particles frequently adopt core-shell or more complex internal structures, likely due to viscous organic components. Ambient morphology is shown to be strongly dependent on the size, as well as contributions from chemical composition and the relative humidity and temperature history of a particle. This has important implications for heterogeneous reactions as organic coatings can inhibit uptake of SOA precursors and the aqueous portion of phase-separated particles is likely to have very different properties (e.g. acidity or ionic strength) than a well-mixed particle with the same composition. It is likely that core-shell or complex structures are prevalent over land and that they play an important role in SOA formation and properties.