Hygroscopicity and CCN Activity of Water‐Soluble Extracts From the Arctic Aerosols in Winter to Early Summer

Abstract

AbstractThe hygroscopicity and cloud condensation nuclei (CCN) activity of water‐soluble extracts from Arctic lower tropospheric aerosols during winter to summer were investigated under sub‐ and super‐saturated conditions, with chemical composition and air mass origin. The κ values from the hygroscopic growth factor at 80%–90% relative humidity (κHTDMA) during winter, spring, and summer were 0.34 ± 0.06, 0.41 ± 0.05, and 0.25 ± 0.02, respectively, whereas those derived from CCN activation diameter at 0.29%–0.59% supersaturation (κCCNC) were 0.42 ± 0.03, 0.43 ± 0.05, and 0.34 ± 0.11, respectively. The hygroscopicity and CCN activity showed clear seasonal variations following changes in composition that are linked to natural, anthropogenic, and biogenic sources. During winter and spring, κ was high when highly hygroscopic components such as sea salts, sulfate, and highly‐oxidized/aged particles were dominant due to long‐range atmospheric transport and photochemical reactions. In contrast, κ was significantly lower in summer when water‐insoluble (22%) and water‐soluble organic matter (OM) (17%) were dominated with high biogenic activity associated with ice‐edge zones. The κCCNC and κHTDMA values agreed well within 8% and the surface tension agreed with that of pure water within 10%. The κ for OM (κOM) estimated from chemical composition during spring and summer was on average 0.04 ± 0.06 (up to ∼0.17). This result suggests that highly hygroscopic components such as sea salt and sulfate mainly controlled particle hygroscopicity and CCN activity in winter, but water‐soluble OM could also contribute in spring and summer.