Optical Properties, Hygroscopicity, and Morphology of Β-Caryophyllene Secondary Organic Aerosol

One of the largest uncertainties in our climate system is the interaction between solar and terrestrial radiation and aerosol particles. Due to the changing composition and morphology of aerosol particles in the atmosphere, determining the optical properties can pose a challenge. Optical properties can be impacted when aerosol particles continually take up and release water. In this study, we investigate the optical properties, water uptake behavior, and morphology of aerosol particles formed from the oxidation β-caryophyllene, a common sesquiterpene. Using cavity ring-down spectroscopy (CRDS) at a wavelength of 643 nm, we characterize the optical properties and hygroscopicity of β-caryophyllene secondary organic aerosol (SOA). Through scanning mobility particle sizing (SMPS), we have investigated the ideal experimental conditions for the concentrations of ozone, β-caryophyllene, and ammonium sulfate seeds and their respective flow rates. The morphology of the particles was determined using transmission electron microscopy (TEM), where the majority of the particles were spherical and core-shell, but some partially-engulfed structures were observed. The analyses from this study will offer a complete characterization of the experimental conditions that are ideal for the study of β-caryophyllene SOA through CRDS and TEM. These experiments may have implications for estimates of radiative forcing, as optical properties are sensitive to particle morphology.