In-Situ Observations Of Aerosol Hygroscopicity And Cloud Droplet Formation In Ny-Ålesund, Svalbard, During Fall 2019 And Spring 2020

The Arctic region suffers an extreme vulnerability to climate change, with an increase in surface air temperatures that have reached twice the global rate during several decades (McBean et al., 2005). The role of clouds, and in particular low-levels clouds and fog, in this arctic amplification by regulating the energy transport from and to space has recently gained interest among the scientific community. The NASCENT 2019-2020 campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) based in Ny-Ålesund, Svalbard (79º North) aimed at studying the microphysical and chemical properties of low-level clouds using measurements both at the sea level and at the Zeppelin station (475 m a.s.l.). First results using a scanning mobility particle sizer (SMPS) and a cloud condensation nuclei counter (CCNC) confirmed that aerosol concentrations in the range 10 < Dpart [nm] < 500 were approximatively 4-5 times higher during the months of Spring 2021 compared to those of Fall 2020. In addition, we found filterpack-derived values of the aerosol hygroscopic parameter κ around 0.7. Combined with temperature and pressure data, these results were used as input parameters for the Morales Betancourt and Nenes (2014) parameterization in order to investigate the susceptibility of droplet formation, which has recently been shown to be highly dependent on aerosol levels in European alpine valleys (Georgakaki et al., 2021). We found strong variations between the Fall to Winter months, known for pristine-like conditions, and the higher particle concentrations generally found in Spring, known as the arctic haze. Specifically, droplet formation was always limited by the low aerosol concentrations in Fall/Winter, whereas updraft-limited cloud formation occurred in Spring. Reviewing relevant literature tells that the relationship between the limiting droplet number concentration and the updraft velocity during NASCENT agrees with that of various locations worldwide, which tends to confirm the universality of this relationship. Georgakaki, P., Bougiatioti, A., Wieder, J., Mignani, C., Ramelli, F., Kanji, Z. A., Henneberger, J., Hervo, M., Berne, A., Lohmann, U., and Nenes, A.: On the drivers of droplet variability in alpine mixed-phase clouds, 21, 10993–11012, https://doi.org/10.5194/acp-21-10993-2021, 2021. McBean, G., Alekseev, G., Chen, D., Førland, E., Fyfe, Groisman, J., P. Y., King, R., Melling, H., Voseand, R., Whitfield, P. H.: Arctic climate: past and present. Arctic Climate Impacts Assessment (ACIA), C. Symon, L. Arris and B. Heal, Eds., Cambridge University Press, Cambridge, 21-60, 2005. Morales Betancourt, R. and Nenes, A.: Droplet activation parameterization: the population-splitting concept revisited, 7, 2345–2357, https://doi.org/10.5194/gmd-7-2345-2014, 2014.