Abstract View
The Interconnection of Aerosol-Phase State and Chemical Composition Impact the Formation and Climate-Altering Properties of Isoprene-Derived Secondary Organic Aerosols
YUE ZHANG, Yuzhi Chen, Martin Wolf, Andrew Lambe, Nicole Olson, Ziying Lei, Zhenfa Zhang, Avram Gold, John Jayne, Douglas Worsnop, Timothy Onasch, Daniel Cziczo, Andrew Ault, Jason Surratt, University of North Carolina at Chapel Hill
Abstract Number: 527
Working Group: Aerosol Chemistry
Abstract
Aerosol phase state, governed by aerosol composition, relative humidity (RH), and temperature, influences the reactive uptake process of gas-phase precursors by altering diffusion rates within particles. Previous studies have systematically examined the reactive uptake probability of isoprene-derived epoxydiols (γIEPOX) onto acidic ammonium sulfate particles coated with α-pinene or surrogate SOA by coupling a flow tube reactor with an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). Given the complex chemical composition of atmospheric aerosols, a parameterized model is needed to address how chemical composition systematically impacts IEPOX-derived SOA.
A uniform layer of organics generated from selected atmospherically relevant SOA precursors was coated onto acidic sulfate particles in a potential aerosol mass (PAM) oxidation flow reactor, and confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Measured γIEPOX was parameterized as a function of SOA coating type, coating thickness, oxidation state, and RH. Results show that certain pre-existing anthropogenic SOA coatings reduced γIEPOX to a higher extent than biogenic SOA coatings of the same thickness, in some cases by nearly an order of magnitude. A multivariate model combining the measured oxidation state and chemical composition of the aerosols was constructed to predict the viscosity of SOA as a function of chemical composition and aerosol water content. The multivariate model on viscosity was combined with a box model with ambient measurement input from the 2013 SOAS campaign to assess the effects of pre-existing organic coatings on IEPOX-derived SOA formation in the Southeast U.S. We show that the oxygen-to-carbon (O/C) and the hydrogen-to-carbon (H/C) ratios of organic shell impact both the phase state and the subsequent IEPOX-derived SOA formation in the presence of an existing SOA coating. The model developed during this study should be applicable to other multiphase chemical systems in regional- and global-scale models to better predict the impact of SOA on climate, human health, and visibility.