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Clouds play an important role in controlling the radiative energy budget of the Arctic atmospheric boundary layer. To quantify their impact on diabatic heating or cooling of the atmosphere and of the surface, vertical profile observations of thermal-infrared irradiances were collected using a tethered balloon. We present 70 profiles of thermal-infrared radiative quantities measured in summer 2020 at the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, and in autumn 2021 and spring 2022 in Ny-Ålesund, Svalbard. Measurements are classified into four groups: cloudless, low-level liquid-bearing cloud, elevated liquid-bearing cloud, and elevated ice cloud. Cloudless cases display a radiative cooling rate of about -2Kday-1. Observed low-level liquid-bearing clouds are characterized by a radiative cooling up to -80Kday-1 in a shallow layer at cloud top. Radiative transfer simulations are performed to quantify the sensitivity of radiative cooling rates to cloud microphysical properties. In particular, cloud top cooling has a strong response to variation of the liquid water path, especially in optically thin clouds, while for optically thick clouds the cloud droplet number concentration has an increased relative importance. Two case studies with a changing cloud cover are presented to investigate the temporal evolution of radiation profiles during the transitions between (a) cloudy to cloudless and (b) low-level to elevated clouds. Additional radiative transfer simulations are used to reproduce the observed scenarios and to showcase the radiative impacts of elevated liquid and ice clouds, demonstrating the increased radiative significance of the liquid clouds. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is a short-lived climate forcer affecting Arctic climate through multiple mechanisms, which vary substantially from winter to summer. Several models still fail in reproducing BC seasonal variability, limiting the ability to fully describe BC climate implications. This study aims at gaining insights into the mechanisms controlling BC transport from lower latitudes to the Arctic lower troposphere. Here we investigate the drivers controlling black carbon daily and seasonal variability in the Arctic using Generalized Additive Models (GAM). We analysed equivalent black carbon (eBC) concentration measured at the Gruvebadet Atmospheric Laboratory (GAL - Svalbard archipelago) from March 2018 to December 2021. The eBC showed a marked seasonality with higher values in winter and early spring. The eBC concentration averaged 22 ± 20 ng m-3 in the cold season (November - April) and 11 ± 11 ng m-3 in the warm season (May - October). The seasonal and interannual variability was mainly modulated by the efficiency of wet scavenging removal during transport towards the higher latitudes. Conversely, the short-term variability was controlled by boundary layer dynamics, local-scale, and synoptic-scale circulation patterns. During both the cold and the warm season, the transport of air masses from western Europe and northern Russia was an effective pathway for the transport of pollution to the European Arctic. Finally, in the warm season we observed a link between the intrusion of warm air from lower latitudes and the increase in eBC concentration. Changes in synoptic scale circulation system and precipitation rate in the northern hemisphere, linked to climate change, are expected to modify BC burden in the Arctic. [ABSTRACT FROM AUTHOR]

Estimating aerosol depositions on snow and ice surfaces and assessing the aerosol lifecycle in the Arctic region is challenged by the scarce available measurement data for particle surface fluxes. This work aims at assessing the deposition velocity of atmospheric particles at an Arctic site (Ny-Ålesund, Svalbard Islands) over snow, during the melting season and over dry tundra. The measurements were performed using the eddy-covariance method from March to August 2021. The measurement system was based on a condensation particle counter (CPC) for ultrafine particle (UFP, < 0.25 µm) fluxes and an Optical Particle Counter (OPC) for evaluating particle size fluxes in the accumulation mode (ACC, 0.25 < dp < 0.7 µm) and quasi-coarse mode (CRS, 0.8 < dp < 3 µm). Turbulent fluxes in the ultrafine particle size range resulted prevalently downward especially in summertime. By contrast, particles fluxes in the accumulation and quasi-coarse mode were more frequently positive especially during the colder months, pointing to surface sources of particles from e.g., sea spray, snow sublimation or local pollution. The overall median deposition velocity (Vd+) values were 0.90, 0.62 and 4.42 mm s-1, for UFP, ACC and CRS, respectively. Deposition velocities were smaller, on average, over the snowpack with median values of 0.73, 0.42 and 3.50 mm s-1. The observed velocities differ of less than 50% respect to previous literature in analogous environments (i.e. ice/snow) in the particles in the size range 0.01-1 µm. At the same time, an agreement with the results of predictive models was found for only a few parameterizations, especially with Slinn (1982), while large biases were found with other models especially in the range 0.3 - 10 µm of particle diameters. Our observations show better fit with the models predicting a minimum deposition velocities for small accumulation mode particle sizes (0.1 - 0.3 µm) rather than for larger ones (~ 1 µm), which could result from an efficient interception of particles over snow surfaces which are rougher than the idealized ones. Finally, a polynomial fit parameterization was proposed in this study to describe the deposition velocity observations which properly represents their size-dependence and magnitude. [ABSTRACT FROM AUTHOR]

Ice nucleating particles (INPs) initiate primary ice formation in Arctic mixed-phase clouds (MPCs), 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 MPCs 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 NINP) during the observation season were approximately up to three orders of magnitude lower compared to the global average, with several samples showing degradation of NINP 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 NINP 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 FROM AUTHOR]

Black Carbon (BC) is a significant forcing agent in the Arctic, but substantial uncertainty remains to quantify its climate effects due to the complexity of the different mechanisms involved, in particular related to processes in the snow-pack after deposition. In this study, we provide detailed and unique information on the evolution and variability of BC content in the upper surface snow layer during the spring period in Svalbard (Ny-Ålesund). Two different snow-sampling strategies were adopted during spring 2014 and 2015, providing the refractory BC (rBC) mass concentration variability on a seasonal/daily and daily/hourly time scales. The present work aims to identify which atmospheric variables could interact and modify the mass concentration of BC in the upper snowpack, the snow layer which BC particles affects the snow albedo. Despite the low BC mass concentrations, a relatively high daily variability was observed. Atmospheric, meteorological, and snow-related physico -chemical parameters were considered in a multiple statistical model to separate the factors determining observations. Precipitation events were the main drivers of the BC variability. Snow metamorphism and activation of local sources during the snow melting periods appeared to play a non-negligible role (wind resuspension in specific Arctic areas where coal mines were present). The BC content in the snow resulted in being statistically decoupled from the atmospheric BC load. [ABSTRACT FROM AUTHOR]

Understanding aerosol-cloud-climate interactions in the Arctic is key to predict the climate in this rapidly changing region. Whilst many studies have focused on submicron aerosol (diameter less than 1 µm), relatively little is known about the climate relevance of supermicron aerosol (diameter above 1 µm). Here, we present a cluster analysis of multiyear (2015-2019) aerodynamic volume size distributions with diameter ranging from 0.5 to 20 µm measured continuously at the Gruvebadet Observatory in the Svalbard archipelago. Together with aerosol chemical composition data from several online and offline measurements, we apportioned the occurrence of the coarse-mode aerosols to anthropogenic (two sources, 27%) and natural (three sources, 73%) origins. Specifically, two clusters are related to Arctic haze with high levels of black carbon, sulfate and accumulation mode (0.1-1 µm) aerosol. The first cluster (9%) is attributed to ammonium sulfate-rich Arctic haze particles, whereas the second one (18%) to larger-mode aerosol mixed with sea salt. The three natural aerosol clusters were: open ocean sea spray aerosol (34%), mineral dust (7%), and an unidentified source of sea spray-related aerosol (32%). The results suggest that sea spray-related aerosol in polar regions may be more complex than previously thought due to short/long-distance origins and mixtures with Arctic haze, biogenic and likely snow-blowing aerosols. Studying supermicron natural aerosol in the Arctic is imperative for understanding the impacts of changing natural processes on Arctic aerosol. [ABSTRACT FROM AUTHOR]

Black Carbon (BC) is a major forcing agent in the Arctic but substantial uncertainty remains to quantify its climate effects due to the complexity of mechanisms involved. In this study, we provide unique information on processes driving the variability of BC mass concentration in surface snow in the Arctic. Two different snow-sampling strategies were adopted during spring 2014 and 2015, focusing on the refractory BC (rBC) mass Ny-Ålesund concentration daily/hourly variability on a seasonal/daily time scale (referred to as 80-days and 3-days experiments). Despite the low rBC mass concentrations (never exceeding 22 ng g-1), a daily variability of up to 4.5 ng g-1 was observed. Atmospheric, meteorological and snow-related physico-chemical parameters were considered in multiple statistical models to understand the factors behind the observed variation of rBC mass concentrations. Results indicate that the main drivers of the variation of rBC are the precipitations events, snow metamorphism (melting-refreezing cycles, surface hoar formation and sublimation) and the activation of local sources (wind resuspension) during the snow melting periods. The rBC in the snow seems de-coupled with the atmospheric BC load. Our results highlighted a common association of snow rBC with coarse mode particles number concentration and with snow precipitation events. [ABSTRACT FROM AUTHOR]

The current inadequate understanding of ice nucleating particle (INP) sources in the Arctic region affects the uncertainty in global radiative budgets and in regional climate predictions. In this study, we present atmospheric INP concentrations by offline analyses on samples collected at ground level in Ny-Ålesund (Svalbard), in spring and summer 2018. The ice nucleation properties of the samples were characterized by means of two offline instruments: the Dynamic Filter Processing Chamber (DFPC), detecting condensation freezing INPs, and the West Texas Cryogenic Refrigerator Applied to Freezing Test system (WT-CRAFT), measuring INPs by immersion freezing. Both measurements agreed within an order of magnitude although with some notable offset. INP concentration measured by DFPC ranged 33-185 (median 88), 5-107 (50) and 3-66 (20) m−3, for T = −22, −18 and −15 °C, respectively, while at the same activation temperatures WT-CRAFT measured 3-199 (26), 1-34 (6) and 1-4 (2) m−3, with an offset apparently dependent on the INP activation temperature. This observation may indicate a different sensitivity of Arctic INPs to different ice nucleation modes, even though a contribution from measurement and/or sampling uncertainties cannot be ruled out. An increase in the coarse INP fraction was observed from spring to summer, particularly at the warmest temperature (up to ~ 70 % at −15 °C). This suggests a non-negligible contribution from local sources of biogenic aerosol particles. This conclusion is also supported by the INP temperature spectra, showing ice-forming activity at temperatures higher than −15 °C. Contrary to recent works (e.g., INP measurements from Ny-Ålesund in 2012), our results do not show a sharp spring-to-summer increase of the INP concentration, with distinct behaviors for particles active in different temperature ranges. This likely indicates that the inter-annual variability of conditions affecting the INP emission by local sources may be wider than previously considered and suggests a complex interplay between INP sources. This demonstrate the necessity of further data coverage. Analysis of INP concentrations, active site density, low-travelling back-trajectories (< 500 m) and ground conditions during the air mass passage suggest that the summertime INP population may be contributed both by terrestrial and marine sources. Air masses in contact with snow-free land had higher INP concentrations, likely reflecting the higher nucleation ability of terrestrial particles. Outside the major terrestrial inputs, the INP population was likely regulated by marine INPs emitted from the sea surface. Evidence of the relation between background INP concentration and the patterns of marine biological activity have been provided by investigating its spatio-temporal correlation with satellite retrieved Chlorophyll-a fields and by the Concentration Weighted Trajectory (CWT) model. The results suggest that sources of INPs may be located both in the seawaters surrounding the Svalbard archipelago and/or as far as Greenland and Iceland. [ABSTRACT FROM AUTHOR]

Sunlit snow is highly photochemically active and plays an important role in the exchange of gas-phase species between the cryosphere to the atmosphere. Here, we investigate the behaviour of two selected species in surface snow: mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the snowpack. However, photo-induced re-emission of gas phase Hg from the surface has been widely reported. Iodine is active in atmosphere new particle formation, especially in the marine boundary layer, and in the destruction of atmospheric ozone. It can also undergo photochemical re-emission. Although previous studies indicate possible post-depositional processes, little is known about the diurnal behaviour of these two species and their interaction in surface snow. The mechanisms are still poorly constrained and no field experiments have been performed in different seasons to investigate the magnitude of re-emission processes. Three high temporal resolution (hourly samples) 3 days long sampling campaign were carried out near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine in surface snow under different sunlight and environmental conditions (24 h-darkness, 24 h-sunlight and day/night cycles). Our results indicate a clearly different behaviour of Hg and I in surface snow during the different campaign. The day/night experiments demonstrate the existence of a diurnal cycle in surface snow for Hg and iodine, indicating that these species are indeed influenced by the daily solar radiation cycle. Differently bromine did not show any diurnal cycle. The diurnal cycle disappeared also for Hg and iodine during the 24 h-sunlight period and during 24 h-darkness experiments supporting the idea of the occurrence (absence) of a continuous recycling/exchange at the snow-air interface. These results demonstrate that this surface snow recycling is seasonally dependent, through sunlight. They also highlight the non-negligible role that snowpack emissions have on ambient air concentrations and potentially on iodine-induced atmospheric nucleation processes. [ABSTRACT FROM AUTHOR]

The aim of the presented study was to investigate the impact on the radiation budget of biomass burning smoke plume transported from Alaska to high Arctic region (Ny-Alesund, Svalbard) in early July 2015. This high aerosol load event is considered exceptional in the last 25 years with mean aerosol optical depth increased by the factor of 10 in comparison to the average summer background values. We utilised in-situ data with hygroscopic growth equations as well as remote sensing measurements as inputs to radiative transfer models with an objective to estimate biases associated with (i) hygroscopicity, (ii) variability of ω profiles and (iii) plane-parallel closure of the modelled atmosphere. A chemical weather model with satellite-derived biomass burning emissions was used to interpret the transport and transformations pathways. Provided MODTRAN simulations resulted in the mean aerosol direct radiative forcing on the level of -78.9 W m-2 and -47.0 W m-2 at the surface and the top of the atmosphere respectively for the mean value of aerosol optical depth equal to 0.64 at 550 nm. It corresponded to the average clear-sky direct radiative forcing of -43.3 W m-2 estimated by radiometers and model simulations. Furthermore, model-derived aerosol direct radiative forcing efficiency reached on average -126 W m-2 / τ550 and -71 W m-2 / τ550 at the surface and at the top of the atmosphere. Estimated heating rate up to 1.8 K day-1 inside the BB plume implied vertical mixing with the turbulent kinetic energy of 0.3 m2 s-2. Ultimately, uncertainty connected with the plane-parallel atmosphere approximation altered results by about 2 W m-2. [ABSTRACT FROM AUTHOR]

The estimation of radon progeny in the Arctic region represents a scientific challenge due to the required low limit of detection in consideration of the limited radon emanation associated with permafrost dynamics. This preliminary study highlighted, for the first time, the possibility to monitor radon progeny in the Arctic region with a higher time resolution. The composition of the radon progeny offered the opportunity to identify air masses dominated by long-range transport, in presence or not of near-constant radon progeny instead of long and short lived progenies. Furthermore, the different ratio between radon and thoron progenies evidenced the contributions of local emissions and atmospheric stability. Two different emanation periods were defined in accordance to the permafrost dynamics at the ground and several accumulation windows were recognized coherently to the meteo-climatic conditions occurring at the study site. [ABSTRACT FROM AUTHOR]

In this paper we present results from a systematic study of vertical profiles of aerosol number size distribution and black carbon (BC) concentrations conducted in the Arctic, over Ny-Ålesund (Svalbard). The campaign lasted 2 years (2011–2012) and resulted in 200 vertical profiles measured during the spring and summer seasons. In addition, chemical analysis of filter samples, aerosol size distribution and a full set of meteorological parameters were determined at ground to put on a firmer grounds the analysis of the vertical profiles. The collected experimental data allowed a classification of the vertical profiles into different typologies which allowed to describe a seasonal phenomenology of vertical aerosol properties in the Arctic. During spring, four main types of profiles were found and their behaviour was related to the main aerosol and atmospheric dynamics occurring at the measuring site. Background conditions generated homogenous profiles. Transport events caused an increase of aerosol concentration with altitude. High Arctic haze pollution trapped below thermal inversions promoted a decrease of aerosol concentration with altitude. Finally, ground-based plumes of locally formed secondary aerosol determined profiles with decreasing aerosol concentration located at different altitude in function of size. During the summer season, the impact from shipping caused aerosol and BC pollution plumes constrained close to the ground, indicating that increasing shipping emissions in the Arctic could bring anthropogenic aerosol and BC in the summer Arctic affecting the climate. [ABSTRACT FROM AUTHOR]

In this paper we present results from a systematic study of vertical profiles of aerosol number size distribution and black carbon (BC) concentrations conducted in the Arctic, over Ny-Ålesund (Svalbard). The campaign lasted 2 years (2011-2012) and resulted in 200 vertical profiles measured during the spring and summer seasons. In addition, chemical analysis of filter samples, aerosol size distribution and a full set of meteorological parameters were determined at ground to put on a firmer grounds the analysis of the vertical profiles. The collected experimental data allowed a classification of the vertical profiles into different typologies which allowed to describe a seasonal phenomenology of vertical aerosol properties in the Arctic. During spring, four main types of profiles were found and their behaviour was related to the main aerosol and atmospheric dynamics occurring at the measuring site. Background conditions generated homogenous profiles. Transport events caused an increase of aerosol concentration with altitude. High Arctic haze pollution trapped below thermal inversions promoted a decrease of aerosol concentration with altitude. Finally, ground-based plumes of locally formed secondary aerosol determined profiles with decreasing aerosol concentration located at different altitude in function of size. During the summer season, the impact from shipping caused aerosol and BC pollution plumes constrained close to the ground, indicating that increasing shipping emissions in the Arctic could bring anthropogenic aerosol and BC in the summer Arctic affecting the climate. [ABSTRACT FROM AUTHOR]