Measurement report: High Arctic aerosol hygroscopicity at sub- and supersaturated conditions during spring and summer

Aerosol hygroscopic growth and cloud droplet formation influence the radiation transfer budget of the atmosphere and thereby the climate. In the Arctic, these aerosol properties may have a more pronounced effect on the climate compared to the midlatitudes. Hygroscopic growth and cloud condensation nuclei (CCN) concentrations of high Arctic aerosols were measured during two field studies in the spring and summer of 2016. The study site was the Villum Research Station (Villum) at Station Nord in the northeastern region of Greenland. Aerosol hygroscopic growth was measured with a hygroscopic tandem differential mobility analyzer (HTDMA) over a total of 23 d, and CCN concentrations were measured over a period of 95 d. Continuous particle number size distributions were recorded, facilitating calculations of aerosol CCN activation diameters and aerosol kappa values. In spring, average CCN concentrations, at supersaturations (SSs) of 0.1% to 0.3 %, ranged from 53.7 to 85.3 cm 3, with critical activation diameters ranging from 130.2 to 80.2 nm and (CCN)-C-kappa ranging from 0.28-0.35. In summer, average CCN concentrations were 20.8 to 47.6 cm 3, while critical activation diameters and (CCN)-C-kappa were from 137.1 to 76.7 nm and 0.23-0.35, respectively. Mean particle hygroscopic growth factors ranged from 1.60 to 1.75 at 90% relative humidity in spring, while values between 1.47 and 1.67 were observed in summer depending on the initial dry size. Although the summer aerosol number size distributions were characterized by frequent new particle formation events, the CCN population at cloud-relevant supersaturations was determined by accumulation-mode aerosols.