(445c) Role of Polarity Distribution of Organics in Aerosol Hygroscopicity

The polarity of organics is a key parameter that may determine the hygroscopic growth of aerosol, cloud droplet activation, and liquid-liquid phase separation (LLPS). However, direct measurements of OA polarity are limited. This study aims to determine the distribution of polarity in OA using the reversed-phase high-performance liquid chromatography (HPLC) and charged aerosol detection (CAD) for the first time. The new measurements showed that water-solubility C (v/v) of secondary organic aerosol (SOA) components produced by the ozonolysis of α-pinene spans nearly six-orders of magnitude. Model simulations of CCN activation show that despite the wide range of solubility, the majority of solutes in α-pinene SOA are dissolved at the point of activation, thus α-pinene SOA may be reasonably assumed as water-soluble especially in the presence of inorganic seeds. Implications of the polarity distribution on LLPS and the gap in sub-saturated and super-saturated aerosol hygroscopicity will be discussed.