AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Effects of Aerosol-Phase State and Chemical Composition on Multiphase Chemistry Leading to Isoprene-Derived Secondary Organic Aerosol Formation
YUE ZHANG, Yuzhi Chen, Andrew Lambe, Nicole Olson, Ziying Lei, Manjula Canagaratna, Jordan Krechmer, Rebecca Craig, Zhenfa Zhang, Avram Gold, John Jayne, Douglas Worsnop, Timothy Onasch, Cassandra Gaston, Joel A. Thornton, William Vizuete, Andrew Ault, Jason Surratt, Univ. of North Carolina, Chapel Hill/Aerodyne Research, Inc.
Abstract Number: 702 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. This laboratory study systematically examined the reactive uptake probability of isoprene-derived epoxydiols (γIEPOX) onto acidic ammonium sulfate particles with selected types of anthropogenic SOA coatings by coupling a flow tube reactor with an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). A uniform layer of organics was coated onto the acidic sulfate particles by using the potential aerosol mass (PAM) oxidation flow reactor, confirmed via 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 significantly reduced the γIEPOX when compared with the γIEPOX for biogenic SOA coatings, in some cases by nearly an order of magnitude for the same coating thickness.
Particle composition was analyzed by both online and offline analytical techniques, including an aerosol chemical speciation monitor (ACSM) and ion mobility spectrometry-mass spectrometry (IMS-MS). A multivariant model combining the measured oxidation state and chemical compositions of the aerosols was constructed to predict the viscosity of SOA as a function of chemical compositions and RH. A box model with ambient measurements from the 2013 SOAS campaign was used to assess the effects of pre-existing organic coatings on IEPOX-derived SOA formation. Our results suggest that the chemical composition and RH jointly influence the phase state of SOA coating and subsequent multiphase chemical processes. 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.