Abstract. Ice nucleating particles (INPs) initiate primary ice formation in Arctic mixed-phase clouds, altering cloud radiative properties and modulating precipitation. For atmospheric INPs, the complexity of their spatiotemporal variations, heterogeneous sources and evolution via intricate atmospheric interactions challenge the understanding of their impact on microphysical processes in Arctic mixed-phase clouds and induce an uncertain representation in climate models. In this work, we performed a comprehensive analysis of atmospheric aerosols at the Arctic coastal site in Ny-Ålesund (Svalbard, Norway) from October to November 2019, including their ice nucleation ability, physicochemical properties and potential sources. Overall, INP concentrations during the observation season were approximately up to three orders of magnitude lower compared to the global average, with several samples showing degradation of INP concentrations after heat treatment, implying the presence of proteinaceous INPs. Particle fluorescence was substantially associated with INP concentrations at warmer ice nucleation temperatures, indicating that in the far-reaching Arctic, aerosols of biogenic origin throughout the snow- and ice-free season may serve as important INP sources. In addition, case studies revealed the links between elevated INP concentrations to heat-lability, fluorescence, high wind speeds originating from the ocean, augmented concentration of coarse-mode particles and abundant organics. Backward trajectory analysis demonstrated a potential connection between high-latitude dust sources and high INP concentrations, while prolonged air mass history over the ice pack was identified for most scant INP cases. The combination of the above analyses demonstrates the abundance, physicochemical properties and potential sources of INPs in the Arctic are highly variable despite its remote location.
Abstract. The Arctic is one of the most rapidly warming regions of the globe. Low-level clouds and fog modify the energy transfer from and to space and play a key role in the observed strong Arctic surface warming, a phenomenon commonly termed "Arctic amplification". The response of low-level clouds to changing aerosol characteristics throughout the year is therefore an important driver of Arctic change that currently lacks sufficient constraints. As such, during the NASCENT campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) extending over a full year from October 2019 to October 2020, microphysical properties of aerosols and clouds were studied at the Zeppelin station (475 m a.s.l.), Ny-Ålesund, Svalbard, Norway. Particle number size distributions obtained from differential mobility particle sizers as well as chemical composition derived from filter samples and an aerosol chemical speciation monitor were analyzed together with meteorological data, in particular vertical wind velocity. The results were used as input to a state-of-the-art cloud droplet formation parameterization to investigate the particle sizes that can activate to cloud droplets, the levels of supersaturation that can develop, the droplet susceptibility to aerosol and the role of vertical velocity. We evaluate the parameterization and the droplet numbers calculated through a droplet closure with in situ measurements. A remarkable finding is that, for the clouds sampled in situ, closure is successful in mixed-phase cloud conditions regardless of the cloud glaciation fraction. This suggests that secondary ice production through ice-ice collisions or droplet-shattering may explain the high ice fraction, as opposed to rime-splintering that would significantly reduce the cloud droplet number below levels predicted by warm cloud activation theory. We also show that pristine-like conditions during fall led to clouds that formed over an aerosol-limited regime, with high levels of supersaturation (generally around 1 %, although highly variable) that activate particles smaller than 20 nm in diameter. Clouds formed in the same regime in late spring and summer, but aerosol activation diameters were much larger due to lower cloud supersaturations (c.a. 0.5 %) that develop because of higher aerosol concentrations and lower vertical velocities. The contribution of new particle formation to cloud formation was therefore strongly limited, at least until these newly formed particles started growing. However, clouds forming during the Arctic haze period (winter and early spring) can be limited by updraft velocity, although rarely, with supersaturation levels dropping below 0.1 % and generally activating larger particles (20 to 200 nm), including pollution transported over a long range. The relationship between updraft velocity and the limiting cloud droplet number agrees with previous observations of various types of clouds worldwide, which tends to confirm the universality of this relationship.
<p>The Arctic region is sensitive to climate change, experiencing accelerated warming. Cloud radiative properties and related feedback mechanisms on Arctic climate are highly uncertain and dependent on the cloud phase. Primary ice formation in Arctic mixed-phase clouds is initiated by INPs. So far, little is known regarding the abundance, variability, and potential sources of INPs in the Arctic owing to the scarcity of data, particularly in the marine environment. We study the INP-cloud interactions to improve the understanding of the abundance and sources of INPs in this region. &#160;We present results from a cruise-based Arctic Century Expedition, which took place from 5 August to 6 September 2021 in the previously uncharted Kara and Laptev Sea in the Eurasian Arctic. Ship-borne INP concentrations (immersion mode) and their spatiotemporal variabilities will be presented and linked to the physicochemical properties of ambient aerosols, including particle size distribution, heat lability, chemical compositions, and biological activities. Additionally, geographical variability of INPs along the ship track are investigated to assess the influence from different origins, e.g., sea ice, marine or terrestrial origins. Ultimately, we will report the results from the in-situ aerosol generator experiments to reveal the phase partitioning of INPs at the sea-air interface highlighting the importance of the aerosolization mechanisms to the production of marine INPs.</p>
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