AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Gas-particle Partitioning of Atmospheric Aerosols: Interplay of Physical State, Non-ideal Mixing and Morphology
MANABU SHIRAIWA, Andreas Zuend, Allan Bertram, John Seinfeld, California Institue of Technology
Abstract Number: 343 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosols, comprising organic compounds and inorganic salts, play a key role in air quality and climate. Mounting evidence exists that these particles frequently exhibit phase separation into predominantly organic and aqueous electrolyte-rich phases. As well, the presence of amorphous semi-solid or glassy particle phases has been established. Using the canonical system of ammonium sulfate mixed with organics from the ozone oxidation of α-pinene, we illustrate theoretically the interplay of physical state, non-ideality, and particle morphology affecting aerosol mass concentration and the characteristic timescale of gas-particle mass transfer.
The state-of-the-art thermodynamic model AIOMFAC (Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients; Zuend et al., 2008; 2011) is used to investigate the effect of phase separation on secondary organic aerosol formation. We demonstrate that phase separation can significantly affect hygroscopic growth and gas-particle partitioning (particle mass and chemical composition). In addition, we estimate the equilibration timescale of SOA gas-particle partitioning using a state-of-the-art kinetic flux model (KM-GAP; Shiraiwa et al., 2012). We demonstrate that semi-solid or glassy phases may kinetically inhibit the gas-particle partitioning and hygroscopic growth especially under low relative humidity and temperature. Thus, the interplay of physical state, non-ideal mixing and morphology have significant implications for the interpretation of laboratory data and the development of improved atmospheric air quality and climate models.