AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Single Particle Morphology and Phase State Analysis of Secondary Organic Aerosol Particles
NICOLE OLSON, Rebecca Craig, Ziying Lei, Yue Zhang, Yuzhi Chen, Amy Bondy, Jason Surratt, Andrew Ault, University of Michigan
Abstract Number: 733 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract A large fraction of submicron organic particulate matter (PM) is formed by the condensation of volatile organic compound (VOC) oxidation products onto pre-existing aerosol particles, thus leading to the formation of secondary organic aerosol (SOA). Isoprene epoxydiol (IEPOX) isomers have been identified as key products of isoprene photo-oxidation under low nitric oxide conditions, which partition to the aerosol phase and undergo further reaction to form isoprene-derived SOA. Traditionally, the aerosol particles where these organic species condense are considered to be homogenous mixtures at thermodynamic equilibrium. However, chamber and field studies have observed more complex physicochemical properties, including organic coatings onto inorganic particles, liquid-liquid phase separations, and viscous or glassy organic phases. To determine the impact of these complex morphologies on the formation of IEPOX-derived SOA, laboratory experiments were conducted by exposing gaseous IEPOX to acidic inorganic sulfate particles mixed with varying amounts and types of SOA precursors (e.g. alpha-pinene or toluene) at a range of relative humidities (15, 30, and 50%).To determine individual particle morphology and internal structure, single particle microscopic and spectroscopic techniques including scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDX), Raman microspectroscopy, and atomic force microscopy with infrared spectroscopy (AFM-IR) were used. A range of morphologies were observed, which may have impacted IEPOX uptake and subsequent particle growth. Understanding the individual particle properties that have the greatest impact on SOA formation is crucial to eventually predicting the formation, evolution, and fate of SOA under a range of atmospheric conditions.