10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Equilibration Timescale of Atmospheric Secondary Organic Aerosol Partitioning under a Wide Range of Temperature and Relative Humidity
YING LI, Manabu Shiraiwa, University of California Irvine
Abstract Number: 622 Working Group: Aerosol Modeling
Abstract Secondary organic aerosol (SOA) formed from partitioning of oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs) accounts for a substantial portion of atmospheric particulate matter. Traditionally, SOA particles have been assumed to be homogeneous and well-mixed liquids and the VOCs oxidation products rapidly establish a gas-particle equilibrium partitioning. However, recent laboratory experiments as well as atmospheric measurements have demonstrated that SOA can occur in amorphous solid or semi-solid phase states, which may result in a kinetically-limited growth rather than the quasi-equilibrium growth. Simulations of the equilibration timescale (τeq) of SOA gas-particle partitioning under room temperature found τeq could be up to hours or days for organic aerosol associated with semi-solid particles (Shiraiwa & Seinfeld, 2012). It is important to further assess the temperature and relative humidity conditions under which such a dynamic formulation of SOA formation is required. This study applies a state-of-the-art kinetic flux model KM-GAP (Shiraiwa et al., 2012) to evaluate the timescale to achieve gas−particle equilibrium under a wide range of temperature and relative humidity. Effects of volatilities of condensing species, pre-existing particle sizes and number concentrations on τeq are also assessed. This study has implications in gas-particle interactions in the free and upper troposphere where particles may occur mainly as amorphous semi-solid or glassy phase states (Shiraiwa et al., 2017).
References: 1. Shiraiwa and Seinfeld (2012), Equilibration timescale of atmospheric secondary organic aerosol partitioning, Geophys. Res. Lett., 39, doi:10.1029/2012GL054008. 2. Shiraiwa, et al. (2012), Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water, Atmos. Chem. Phys., 12, 2777-2794. 3. Shiraiwa, et al. (2017), Global distribution of particle phase state in atmospheric secondary organic aerosols, Nat. Commun., 8:15002.