AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Spreading Ratio and Morphology of Size-dependent Secondary Organic Aerosols
ZIYING LEI, Nicole Olson, Yue Zhang, Yuzhi Chen, Andrew Lambe, Natalie White, Joanna Atkin, Jason Surratt, Andrew Ault, University of Michigan
Abstract Number: 277 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA), accounting for a large portion of the atmospheric particulate matter, are formed by oxidation of volatile organic compounds (VOC). VOC oxidation products either nucleate, condense, or undergo multiphase chemical processes that contribute to SOA mass loadings. Resolving the chemical complexity, morphology, and viscosity of SOA is crucial for understanding the impacts of atmospheric aerosols. Viscosity can be defined in terms of the spreading ratio of impacted particles. The chemical composition of particles and relative humidity (RH) both affect viscosity and need to be accounted for when determining and predicting aerosol particle spreading ratios. However, the viscosity of atmospheric particles is currently poorly quantified, and understanding the relationship between spreading ratios of size-selected aerosol particles and viscosity is still incomplete. Morphology also plays an important role in understanding atmospheric aerosols since it affects mixing state, heterogeneous chemical reactions, and optical properties, but is hard to quantify in SOA models due to complex chemical compositions and diverse ambient conditions.
This study investigated size-dependent spreading ratios and morphologies of four different types of SOA, such as toluene SOA, α-pinene SOA, isoprene SOA, and β-caryophyllene SOA. To determine spreading ratio as a function of particle chemical composition and size, laboratory experiments were conducted on four types of size-selected SOA particles (150nm, 200nm, and 250nm) at 50% RH. Atomic force microscopy coupled with infrared spectroscopy (AFM-IR) and Raman spectroscopy were used to characterize morphology, spreading ratio, and chemical composition of individual SOA particles. Results show that phase separation frequently occurred; specifically, core-shell and partially-engulfed morphologies were observed for the four types of SOA examined. Spreading ratios significantly changed as a function of the SOA precursor, which can be used to improve estimates of SOA physicochemical properties.