Characterization of the physicochemical properties of secondary organic aerosols formed by photo-oxidation of toluene in the atmospheric processes simulation chamber, K-CAPS

A series of experiments was conducted to characterize a medium-sized 27-m³ smog chamber, KIST atmospheric processes simulation chamber (K-CAPS) in terms of the gas and particle wall losses, spectrum of light sources, and background reactivity and evaluate its suitability for simulating atmospheric reactions. Photo-oxidation experiments using a toluene and NO_x mixture were then carried out to investigate the effects of the UV lamp type, UV intensity, and ammonium sulfate seeds on the formation of secondary organic aerosols (SOA) and O₃, and on the physicochemical properties of SOA including hygroscopicity. When UVA and UVB lamps were used together, formation of SOA and O₃ was faster than that for UVA lamps alone. And higher UV intensity also resulted in faster formation of SOA and O₃, but the increase in O₃ with accumulated OH exposure and the increase in SOA with reacted toluene concentrations are consistent regardless of photolysis rate of NO₂ implying that increment in UV intensity can be acceptable to shorten the experiment time for relatively long aging processes such as multiday reactions. More SOA and less O₃ were formed when ammonium sulfate seeds were initially injected and average RH was relatively higher, compared to the dry experiment without seeds. These results must be useful to understand the physicochemical properties of SOA formed through photo-oxidation of anthropogenic VOCs in real-world atmospheric conditions.