In atmospheric particles, organic species become mixed with inorganic species via gas-phase oxidation of volatile organic compounds (VOCs) with subsequent condensation of the low-volatility products, such as isoprene epoxydiols (IEPOX), key products of isoprene photo-oxidation. This process leads to the formation of secondary organic aerosol (SOA), a ubiquitous component of submicron aerosols. Chamber and field studies have observed complex physicochemical properties of SOA, such as liquid-liquid phase separations (LLPS) and viscous or glassy organic phases that inhibit reactive uptake of gaseous species, lower partitioning of chemical species from particle to gas phase, and lower the relative humidity (RH) at which particles undergo efflorescence and deliquescence. To determine the impact these complex morphologies have on the formation of IEPOX-derived SOA, laboratory experiments were conducted by exposing gaseous IEPOX to acidic ammonium sulfate particles coated with α-pinene and toluene SOA over a range of RH (15-50%).To determine individual particle morphology and viscosity, 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 (AFM) were used. After IEPOX uptake, changes to particle morphology and an increase in particle viscosity were observed, which decreased additional IEPOX uptake and limited subsequent particle growth. These results indicate that particle phase and viscosity determination is necessary to more accurately predict atmospheric fate of ambient aerosols, and the effect aerosols have on heterogeneous (multi-phase) chemistry, climate, and air quality.<br/>

Viscosity increases in the core of phase separated particles after IEPOX uptake

2019 Fall National Meeting

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