Atmospheric Chemistry and Physics Relating CCN activity, volatility, and droplet growth kinetics of β-caryophyllene secondary organic aerosol

Abstract. This study investigates the droplet formation char-acteristics of secondary organic aerosol (SOA) formed dur-ing the ozonolysis of sesquiterpene β-caryophyllene (with and without hydroxyl radicals present). Emphasis is placed on understanding the role of semi-volatile material on Cloud Condensation Nucleus (CCN) activity and droplet growth ki-netics. Aging of β-caryophyllene SOA significantly affects all CCN-relevant properties measured throughout the exper-iments. Using a thermodenuder and two CCN instruments, we find that CCN activity is a strong function of temperature (activation diameter at ∼0.6 % supersaturation: 100±10 nm at 20◦C and 130±10 nm at 35◦C), suggesting that the hygro-scopic fraction of the SOA is volatile. The water-soluble or-ganic carbon (WSOC) is extracted from the SOA and charac-terized with Köhler Theory Analysis (KTA); the results sug