Comment on acp-2022-413: Answer to Anonymous Referee 2

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> 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 mid-latitudes. 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 days, and CCN concentrations were measured over a period of 95 days. Continuous particle number size distributions were recorded, facilitating calculations of aerosol CCN activation diameters and aerosol kappa (&kappa;)-values. In spring, average CCN concentrations, at supersaturations (SS) 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 &kappa;_CCN ranging from 0.28&ndash;0.35. In summer, average CCN concentrations were 20.8 to 47.6 cm^-3, while critical activation diameters and &kappa;_CCN were from 137.1 to 76.7 nm and 0.23&ndash;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 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. This emphasizes the importance of accumulation mode aerosol sources to provide available CCN during summer. The influence of particle hygroscopic growth on the radiative transfer through aerosol-radiation interactions could be of major importance. The results of this study are directly applicable in the modeling of direct and indirect climate effects of Arctic aerosols. Targeted chemical and morphological analysis, based on filter samples or on-line techniques, could further clarify the role of primary organic marine influence on Arctic aerosol CCN concentrations and therewith climate effects.