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This article aims to improve the understanding of the small scale aerosol distribution affected by different atmospheric boundary layer (ABL) properties. In particular, transport and mixing of ultrafine aerosol particles (UFP) are investigated, as an indicator for possible sources triggering the appearance of new particle formation (NPF) at an Arctic coastal site. For this purpose, flexible measurements of unmanned aerial systems (UAS) are combined with continuous ground based observations at different altitudes, the observatory Gruvebadet close to the fjord at an altitude of 67 m above sea level (a.s.l.), and the observatory at the Zeppelin Mountain at an altitude of 472 m a.s.l.. The two unmanned research aircraft called ALADINA and MASC-3 were applied for field activities at the polar research site Ny-Ålesund, Svalbard, between 24 April 2018 and 25 May 2018. The period was at the end of Arctic haze during the snow melt season. A high frequency of occurrence of NPF was observed, namely on 55 % of the airborne measurement days. With ALADINA, 230 vertical profiles were performed between the surface and the main typical maximum height of 850 m a.s.l., and the profiles are connected to surface measurements, in order to obtain a 4-D picture of aerosol particle distribution. Analyses of potential temperature, water vapour mixing ratio and aerosol particle number concentration of UFP in the size range of 3–12 nm (N3−12) indicate a clear impact of the ABL’s stability on the vertical mixing of the measured UFP, which results in systematical differences of particle number concentrations at the two observatories. In general, higher concentrations of UFP occurred near the surface, suggesting the open sea as the main source for NPF. Three different case studies show that the UFP were rapidly mixed in the vertical and horizontal scale depending on atmospheric properties. In case of temperature inversions, the aerosol population stayed confined to specific altitude ranges, and was not always detected at the observatories. However, during another case study that was in relation to a persistent NPF event with subsequent growth rate, the occurrence of UFP was identified to be a wide spreading phenomenon in the vertical scale, as the observed UFP exceeded the height of 850 m a.s.l.. During a day with increased local pollution enhanced equivalent black carbon mass concentration (eBC) coincided with an increase of the measured N3−12 in the lowermost 400 m, but without subsequent growth rate. The local pollution was transported to higher altitudes, as measured by the UAS. Thus, emissions from local pollution may play a role for potential sources for UFP in the Arctic as well. In summary, a highly variable spatial and temporal aerosol distribution was observed with small scales at the polar site Ny-Ålesund, determined by atmospheric stability, contrasting surface and sources, and topographic flow effects. The UAS provides the link to understand differences measured at the two observatories at close distance, but different altitudes.

As part of the “East Antarctic International Ice Sheet Traverse” (EAIIST) project, surface snow and snow pit samples were collected along a traverse from Dome C toward the geographic South Pole during the 2019–2020 Antarctic campaign. Results on spatial distribution of major ions are here reported to understand deposition and post deposition processes in sites with very low snow accumulation rate in the East Antarctic Plateau where megadune and wind crust areas are present. The volcanic signature of Pinatubo eruption (occurred in 1991) was clearly visible in the non-sea salt SO42− stratigraphy from two snow pits (AGO-5 and PALEO) allowing the determination of annual accumulation rates that revealed to be 25.7 and 22.6 mm of water equivalent/year, respectively at the two sites. Moreover, a decreasing trend in accumulation rate as the distance from the Indian Ocean increases was detected. Mineral dust concentration and size show presence of a criptotephra layer in AGO5 and PALEO stratigraphies which is stratigraphically compatible with the deposition of volcanic ash related to the Puyehue-Cordón Caulle explosive eruption occurred in June 2011. The ssNa+ fraction, accounting for the 92.5 % of the total Na+, is preserved stably in the snow layers and was chosen as marker of sea spray deposition. Despite the very low accumulation rate in this area, the main deposition process of sea spray aerosol is the wet deposition. Conversely, both biogenic and crustal nssSO42− are dry deposited, the total flux of nssSO42− resulted to be constant in the Antarctic plateau, but the biogenic to crustal ratio increases as distance from Dome C increases. The presence and quantification (by nssCa2+) of a dry deposited crustal source, as the biogenic one, sheds light on the interpretation of nssSO42− biogenic stratigraphy during glacial and interglacial time in Antarctic ice cores. NssCl− represent the fraction of Cl− deposited as HCl and arises from the exchange reactions between chloride in the sea salt aerosol and acidic species such as H2SO4 and HNO3 that occurs both into the atmosphere (in this case HCl is deposited by wet deposition) and into the snow (at the expenses of NaCl or MgCl2 deposited as sea salt aerosol). The latter process could be particularly efficient in sites affected by wind crust formation, probably because of a longer exposure time of the snow layers to the atmosphere favouring the HCl volatilization . Another important marker in ice core is HNO3, that in the considered sites is found at very high concentration in the most superficial 3 cm of snow due to the uptake by superficial snow and possibly concentration effects from the layers beneath, but it is reversibly deposited. The depth of the active layer for HNO3 reemission was calculated and it spans from 22 cm to 12 cm; in addition, the concentration preserved in the snow decreases as the accumulation rate decreases, but wind scouring increases the efficiency of re-emission processes in the active layer. The knowledge and quantification of all the above reported processes will allow the interpretation of the ice core stratigraphies in low accumulation site likely hopefully recording, at selected sites, the climate history of more than one million years ago.

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.

The main purpose of this work is to propose a mechanism of post-depositional processes affecting chlorine and its chlorine-36 cosmogenic nuclide in the upper snowpack of the High Antarctic Plateau. We suggest that the observed decrease of total chlorine content in the upper meters of the snowpack is due to a progressive release of the HCl content from ice. We also propose a consistent framework, combining diffusion in bulk ice and snow microstructure. The observation of the low chlorine content in ice at depth leads to the robust hypothesis that the chemical equilibrium of chlorine between the ice and the snowpack interstitial air (SIA) is close to zero. HCl is thought to diffuse in ice, and to be progressively released in the SIA, and exported to the Antarctic atmosphere by the wind-ventilation. The time required to expel all the mobile species of chlorine (i.e., HCl) from snow depends on the diffusion coefficient of chlorine in ice combined with the snow grain size and its evolution with depth. This work is synthesised in a model combining the microstructure evolution of the upper meters of a snowpack (changes in mean snow grain size) and the diffusion of chlorine in ice applied to single spherical grains. The variability observed in chloride concentration profiles with depth, at a same site but different sampling time or different snow pits, or among different sites of the High Antarctic Plateau, is mostly due to the variations in initial concentrations in HCl and sodium chloride (NaCl) species and the snow grain size evolution. This model offers a common framework for understanding the fate of chlorine in Antarctica, from coastal to inland locations, including low accumulation sites on the plateau, far from the ocean. Applications of this post-depositional model to chlorine and to 36Cl allows to picture a recycling mechanism of chlorine at the scale of Antarctica. In particular, the 36Cl concentration in the surface snow of the Vostok site illustrates this recycling mechanism and the persistent contamination of inland Antarctica by anthropogenic 36Cl originating from the marine nuclear tests of the 1950s to the 1970s.

Changes in sea ice conditions and atmospheric circulation over the Southern Ocean play an important role in modulating Antarctic climate. However, observations of both sea ice and wind conditions are limited in Antarctica and the Southern Ocean, both temporally and spatially. Ice core chemistry data can be used to reconstruct changes over annual, decadal, and millennial timescales. To facilitate sea ice and wind reconstructions, the CLIVASH2k working group has compiled a database of two species, sodium [Na+] and sulphate [SO42-], commonly measured ionic species. The database contains records from 105 Antarctic ice cores, containing records with a maximum age duration of 2000 years. An initial filter has been applied, based on evaluation against climate observations, to identify sites suitable for reconstructing past sea ice conditions, wind strength, or atmospheric circulation.

In this study, we modeled the aerosol particle formation along air mass trajectories arriving at the remote Arctic research stations Gruvebadet (67 m a.s.l.) and Zeppelin (474 m a.s.l.), Ny-Ålesund, during May 2018. The aim of this study was to improve our understanding of processes governing secondary aerosol formation in remote Arctic marine environments. We run the Lagrangian chemistry transport model ADCHEM, along air mass trajectories generated with FLEXPART v10.4. The air masses arriving at Ny-Ålesund spent most of their time over the open ice-free ocean. In order to capture the secondary aerosol formation from the DMS emitted by phytoplankton from the ocean surface, we implemented a recently developed comprehensive DMS and halogen multi-phase oxidation chemistry scheme, coupled with the widely used Master Chemical Mechanism (MCM). The modeled median particle number size distributions are in close agreement with the observations in the marine-influenced boundary layer near-sea-surface Gruvebadet site. However, while the model reproduces the accumulation mode particle number concentrations at Zeppelin, it overestimates the Aitken mode particle number concentrations by a factor of ∼5.5. We attribute this to the deficiency of the model to capture the complex orographic effects on the boundary layer dynamics at Ny-Ålesund. However, the model reproduces the average vertical particle number concentration profiles within the boundary layer (0–600 m a.s.l.) above Gruvebadet, as measured with condensation particle counters (CPCs) on board an unmanned aircraft system (UAS). The model successfully reproduces the observed Hoppel minima, often seen in particle number size distributions at Ny-Ålesund. The model also supports the previous experimental findings that ion-mediated H2SO4–NH3 nucleation can explain the observed new particle formation in the marine Arctic boundary layer in the vicinity of Ny-Ålesund. Precursors resulting from gas- and aqueous-phase DMS chemistry contribute to the subsequent growth of the secondary aerosols. The growth of particles is primarily driven via H2SO4 condensation and formation of methane sulfonic acid (MSA) through the aqueous-phase ozonolysis of methane sulfinic acid (MSIA) in cloud and deliquescent droplets.

To control the spread of COVID-19, exceptional restrictive measures were taken in March 2020 that imposed a radical change on the lifestyle of millions of citizens around the world, albeit for a short period. The national lockdown, which lasted from 10 March to 18 May 2020 in Italy, was a unique opportunity to observe the variation in air quality in urban environments under conditions comprising almost total traffic restriction and a strong reduction in work activities. In this paper, the data from 17 urban monitoring sites in Tuscany are presented, and the PM and NO2 concentrations in the 2 months before the start of the lockdown and the 2 months after lockdown are compared with the corresponding months of the previous 3 years. The results show that the total loads of PM2.5 and PM10 (particulate matter with an aerodynamic diameter smaller than 2.5 and 10 µm, respectively) decreased, but they did not exhibit significant changes compared to previous years, whereas NO2 underwent a drastic reduction. For three of these sites, the chemical composition of the collected samples was measured using thermal–optical techniques, ion chromatography, and particle-induced X-ray emission analysis, and the application of multivariate positive matrix factorization analysis also allowed for PM10 source identification and apportionment. Using these analyses, it was possible to explain the low sensitivity of PM10 to the lockdown effects as being due to different, sometimes inverse, behaviors of the different sources that contribute to PM. The results clearly indicate a decline in pollution levels related to urban traffic and an increase in the concentration of sulfate for all sites during the lockdown period.

Large volcanic eruptions occurring in the last glacial period can be detected by their accompanying sulfuric acid deposition in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 kyr before 2000 CE (b2k). Over most of the investigated interval the ice cores are synchronized, making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only list Greenland sulfate depositions larger than 20 kg km−2 and Antarctic sulfate depositions larger than 10 kg km−2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 737 eruptions in Antarctica within the 51 kyr period – for which the sulfate deposition of 85 eruptions is found at both poles (bipolar eruptions). Based on the ratio of Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. A total of 25 of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years, and 69 eruptions are estimated to have larger sulfur emission strengths than the Tambora, Indonesia, eruption (1815 CE). Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 ka b2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. This confirms the suggestion that the isostatic unloading of the Northern Hemisphere (NH) ice sheets may be related to the enhanced NH volcanic activity. Our ice-core-based volcanic sulfate records provide the atmospheric sulfate burden and estimates of climate forcing for further research on climate impact and understanding the mechanism of the Earth system.

This paper presents the results on simultaneous high time resolution measurements of biogenic aerosol (methane sulfonic acid-MSA, non-sea salt sulfate nssSO42-) with its gaseous precursor dimethylsulfide (DMS) performed at the Italian coastal base Mario Zucchelli Station (MZS) in Terra Nova Bay (MZS) during two summer campaigns (2018–2019 and 2019–2020). The study provides information on marine biological activity in the nearby polynya in the Ross Sea and on the influence of biogenic and atmospheric processes on biogenic aerosol formation. Data on atmospheric DMS concentration are scarce especially in Antarctica. The DMS-maximum at MZS occurs in December, one month earlier than at other Antarctic stations. The maximum of DMS concentration is connected with the phytoplanktonic senescent phase following the bloom of Phaeocystis antarctica that occurs in the polynya when sea ice opens up. The second plankton bloom occurs in January and, despite the high Dimethylsulfopropionate (DMSP) concentration in sea water, atmospheric DMS remains low probably due to its fast biological turnover in sea water in this period. The intensity and timing of the DMS evolution during the two years suggests that only the portion of the polynya close to the sampling site produces a discernible effect on the measured DMS. The closeness to the DMS source area, and the occurrence of air masses containing DMS and freshly formed oxidation products allow to study the kinetic of biogenic aerosol formation and the reliable derivation of the branch ratio between MSA and nssSO42- from DMS oxidation that is estimated to be 0.84 ± 0.06. Conversely, for aged airmasses with low DMS content, an enrichment of nssSO42- with respect to MSA, due to the presence of background concentration of nssSO42- from volcanic origin (Erebus) or from long range transport, takes place. Therefore, the aged air mass presents an MSA / nssSO42- ratio lower than in newly formed biogenic aerosol. By considering the sum of MSA and biogenic nssSO42-, we estimate that the mean contribution of biogenic particulate matter to PM10 is 17 %, with a maximum of 56 %. The high contribution of biogenic aerosol to the total PM10 mass in summer in this area highlights the dominant role of the polynya on biogenic aerosol formation. Finally, due to the regional and year-to year variability of DMS and related biogenic aerosol formation, we stress the need of long-term measurements of atmospheric DMS and biogenic aerosol along the Antarctic coast and in the Southern Ocean.

We examined the relationships linking atmospheric in-situ data of gas phase methane sulfonic acid (CH3SO3H, MSA), sulfuric acid (H2SO4, SA), iodic acid (HIO3), highly oxidized organic molecules (HOM) and aerosol particle concentrations in the size ranges of 10‒50 nm and 100‒450 nm with satellite-derived chlorophyll a (Chl-a) and oceanic primary production (PP) during two time spans – the phytoplankton early bloom period, April‒May 2017 (30 March‒1 June, springtime) and phytoplankton late bloom; June‒July 2017 (2 June‒4 August, summertime) – in two ocean domains; Greenland Sea and Barents Sea. Atmospheric data were collected at Ny-Ålesund site in Svalbard, Norway. In general, Chl-a and PP in the Barents Sea were higher than in the Greenland Sea during the April‒May period, whereas the Greenland Sea had higher Chl-a and PP during June‒July. Phytoplankton bloom started by the loss of sea ice coverage in the Barents Sea at the marginal ice zone (MIZ) during April‒May, and in the Greenland Sea close to Svalbard Island during June‒July. From the April‒May period to the June‒July period, the correlation between the ocean color data (Chl-a and PP) and MSA decreased in the Barents Sea and increased in the Greenland Sea, which establishes a direct relationship between the sea ice melting, phytoplankton bloom and atmospheric vapour composition. Both MSA and SA concentrations increased strongly during the bloom period, suggesting marine phytoplankton metabolism and resulting dimethyl sulphide (DMS) as the primary source of both MSA and SA in the Arctic atmosphere during spring–summer time. The highest correlation among all the atmospheric components and ocean color properties was observed between HIO3 and Chl-a in both ocean domains during the springtime, but this feature may be connected to processes associated with the melting of sea ice. HOMs showed a low correlation with Chl-a and PP in comparison to other atmospheric vapours. The plausible explanation for such low correlation is that the primary source of volatile organic compounds (VOC) – precursors of HOM – is the soil or terrestrial vegetation of Svalbard archipelago rather than the ocean. In springtime, small-particles (10‒50 nm) correlated strongly with Chl-a in the Barents Sea and with PP in both oceanic domains, suggesting that biogenic productivity has a strong impact on new particle formation (NPF) in the springtime. In the summertime, small-particle concentrations showed almost no correlation with biogenic parameters, indicating that compounds not connected with phytoplankton metabolism, such as HOMs, have a critical role in summertime NPF. Larger particles (100‒450 nm) showed an anti-correlation with Chl-a and PP in springtime, probably due to dilution of anthropogenic air pollution (arctic haze) during spring. In the end of the Arctic haze period in April, particle-phase SA (non-sea-salt sulphate, nss-SO4-2) and particle phase MSA (MS-) showed almost no correlation, whereas a connection between the gas phase MSA and SA concentrations was found. The likely reason for this is the same origin for gas phase MSA and SA (DMS oxidation), whereas SA in particle phase mostly originated from a long-distance continental source.

Optical properties of surface aerosols at Dome C, Antarctica, in 2007–2013 and their potential source areas are presented. Scattering coefficients (σsp) were calculated from measured particle number size distributions with a Mie code and from filter samples using mass scattering efficiencies. Absorption coefficients (σap) were determined with a three-wavelength Particle Soot Absorption Photometer (PSAP) and corrected for scattering by using two different algorithms. The scattering coefficients were also compared with σsp measured with a nephelometer at the South Pole Station (SPO). The minimum σap was observed in the austral autumn and the maximum in the austral spring, similar to other Antarctic sites. The darkest aerosol, i.e., the lowest single-scattering albedo ωo≈0.91, was observed in September and October and the highest ωo≈0.99 in February and March. The uncertainty of the absorption Ångström exponent αap is high. The lowest αap monthly medians were observed in March and the highest in August–October. The equivalent black carbon (eBC) mass concentrations were compared with eBC measured at three other Antarctic sites: the SPO and two coastal sites, Neumayer and Syowa. The maximum monthly median eBC concentrations are almost the same (∼3±1 ng m−3) at all these sites in October–November. This suggests that there is no significant difference in eBC concentrations between the coastal and plateau sites. The seasonal cycle of the eBC mass fraction exhibits a minimum f(eBC) ≈0.1 % in February–March and a maximum ∼4 %–5 % in August–October. Source areas were calculated using 50 d FLEXPART footprints. The highest eBC concentrations and the lowest ωo were associated with air masses coming from South America, Australia and Africa. Vertical simulations that take BC particle removal processes into account show that there would be essentially no BC particles arriving at Dome C from north of latitude 10∘ S at altitudes m. The main biomass-burning regions Africa, Australia and Brazil are more to the south, and their smoke plumes have been observed at higher altitudes than that, so they can get transported to Antarctica. The seasonal cycle of BC emissions from wildfires and agricultural burning and other fires in South America, Africa and Australia was calculated from data downloaded from the Global Fire Emissions Database (GFED). The maximum total emissions were in August–September, but the peak of monthly average eBC concentrations is observed 2–3 months later in November, not only at Dome C, but also at the SPO and the coastal stations. The air-mass residence-time-weighted BC emissions from South America are approximately an order of magnitude larger than from Africa and Oceania, suggesting that South American BC emissions are the largest contributors to eBC at Dome C. At Dome C the maximum and minimum scattering coefficients were observed in austral summer and winter, respectively. At the SPO σsp was similar to that observed at Dome C in the austral summer, but there was a large difference in winter, suggesting that in winter the SPO is more influenced by sea-spray emissions than Dome C. The seasonal cycles of σsp at Dome C and at the SPO were compared with the seasonal cycles of secondary and primary marine aerosol emissions. The σsp measured at the SPO correlated much better with the sea-spray aerosol emission fluxes in the Southern Ocean than σsp at Dome C. The seasonal cycles of biogenic secondary aerosols were estimated from monthly average phytoplankton biomass concentrations obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite sensor data. The analysis suggests that a large fraction of the biogenic scattering aerosol observed at Dome C has been formed in the polar zone, but it may take a month for the aerosol to be formed, be grown and get transported from the sea level to Dome C.

10 pages, 3 figures, 1 table, supporting information https://doi.org/10.1021/acs.est.1c07796, Atmospheric aerosols are important drivers of Arctic climate change through aerosol–cloud–climate interactions. However, large uncertainties remain on the sources and processes controlling particle numbers in both fine and coarse modes. Here, we applied a receptor model and an explainable machine learning technique to understand the sources and drivers of particle numbers from 10 nm to 20 μm in Svalbard. Nucleation, biogenic, secondary, anthropogenic, mineral dust, sea salt and blowing snow aerosols and their major environmental drivers were identified. Our results show that the monthly variations in particles are highly size/source dependent and regulated by meteorology. Secondary and nucleation aerosols are the largest contributors to potential cloud condensation nuclei (CCN, particle number with a diameter larger than 40 nm as a proxy) in the Arctic. Nonlinear responses to temperature were found for biogenic, local dust particles and potential CCN, highlighting the importance of melting sea ice and snow. These results indicate that the aerosol factors will respond to rapid Arctic warming differently and in a nonlinear fashion, This research was supported by the Natural Environment Research Council (grant no. NE/S00579X/1) and endorsed by the Surface Ocean-Lower Atmosphere Study (SOLAS), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

The Arctic atmosphere is warming rapidly and its relatively pristine environment is sensitive to the long-range transport of atmospheric pollutants. While carbon dioxide is the main cause for global warming, short-lived climate forcers (SLCFs) such as methane, ozone, and particles also play a role in Arctic climate on near-term time scales. Atmospheric modelling is critical for understanding the abundance and distribution of SLCFs throughout the Arctic atmosphere, and is used as a tool towards determining SLCF impacts on climate and health in the present and in future emissions scenarios. In this study, we evaluate 18 state-of-the-art atmospheric and Earth system models, assessing their representation of Arctic and Northern Hemisphere atmospheric SLCF distributions, considering a wide range of different chemical species (methane, tropospheric ozone and its precursors, black carbon, sulfate, organic aerosol, and particulate matter) and multiple observational datasets. Model simulations over four years (2008–2009 and 2014–2015) conducted for the 2021 Arctic Monitoring and Assessment Programme (AMAP) SLCF assessment report are thoroughly evaluated against satellite, ground, ship and aircraft-based observations. The results show a large range in model performance, with no one particular model or model type performing well for all regions and all SLCF species. The multi-model mean was able to represent the general features of SLCFs in the Arctic, though vertical mixing, long-range transport, deposition, and wildfire emissions remain highly uncertain processes. These need better representation within atmospheric models to improve their simulation of SLCFs in the Arctic environment.

Organic aerosols in the Arctic are predominantly fuelled by anthropogenic sources in winter and natural sources in summer, according to observations from eight sites across the Arctic Aerosols play an important yet uncertain role in modulating the radiation balance of the sensitive Arctic atmosphere. Organic aerosol is one of the most abundant, yet least understood, fractions of the Arctic aerosol mass. Here we use data from eight observatories that represent the entire Arctic to reveal the annual cycles in anthropogenic and biogenic sources of organic aerosol. We show that during winter, the organic aerosol in the Arctic is dominated by anthropogenic emissions, mainly from Eurasia, which consist of both direct combustion emissions and long-range transported, aged pollution. In summer, the decreasing anthropogenic pollution is replaced by natural emissions. These include marine secondary, biogenic secondary and primary biological emissions, which have the potential to be important to Arctic climate by modifying the cloud condensation nuclei properties and acting as ice-nucleating particles. Their source strength or atmospheric processing is sensitive to nutrient availability, solar radiation, temperature and snow cover. Our results provide a comprehensive understanding of the current pan-Arctic organic aerosol, which can be used to support modelling efforts that aim to quantify the climate impacts of emissions in this sensitive region.

To control the spread of COVID-19, in March 2020 exceptional restrictive measures were taken imposing a radical change in the lifestyle of millions of citizens around the world, albeit for a short period of time. The national lockdown, which in Italy lasted from 10 March to 18 May 2020, was a unique opportunity to observe the variation in air quality in urban environments in a condition of almost total traffic block and a strong reduction in work activities. In this paper, the data from seventeen urban monitoring sites in Tuscany are presented by comparing PM and NO2 of the two months before the start of the lockdown and the two after with the corresponding months of the previous three years. The results show that the total load of PM2.5 and PM10 decreased but it did not exhibit significant changes compared to previous years, while NO2 undergoes a drastic reduction. For three of these sites, the chemical composition of the collected samples was measured by thermo-optical, ion chromatography and PIXE analysis, and the application of multivariate PMF analysis allowed the PM10 source identification and apportionment. Thanks to these analyses it was possible to explain the low sensitiveness of PM10 to the lockdown effects as due to different, sometimes opposite, behaviors of the different sources that contribute to PM. The results clearly indicated a decline in pollution levels related to urban traffic and an increase in the concentration of sulfate for all sites during the lockdown period.

Large volcanic eruptions occurring in the last glacial period can be detected in terms of their deposited sulfuric acid in continuous ice cores. Here we employ continuous sulfate and sulfur records from three Greenland and three Antarctic ice cores to estimate the emission strength, the frequency and the climatic forcing of large volcanic eruptions that occurred during the second half of the last glacial period and the early Holocene, 60–9 ka years before AD 2000 (b2k). The ice cores are synchronized over most of the investigated interval making it possible to distinguish large eruptions with a global sulfate distribution from eruptions detectable in one hemisphere only. Due to limited data resolution and to a large variability in the sulfate background signal, particularly in the Greenland glacial climate, we only detect Greenland sulfate depositions larger than 20 kg km−2 and Antarctic sulfate depositions larger than 10 kg km−2. With those restrictions, we identify 1113 volcanic eruptions in Greenland and 740 eruptions in Antarctica within the 51 ka period – where the sulfate deposition of 85 eruptions is defined at both poles (bipolar eruptions). Based on the relative Greenland and Antarctic sulfate deposition, we estimate the latitudinal band of the bipolar eruptions and assess their approximate climatic forcing based on established methods. The climate forcing of the five largest eruptions is estimated to be higher than −70 W m−2. Twenty-seven of the identified bipolar eruptions are larger than any volcanic eruption occurring in the last 2500 years and 69 eruptions are estimated to have larger sulfur emission strengths than the VEI-7 Tambora eruption that occurred in Indonesia in 1815 AD. The frequency of eruptions larger than the typical VEI-7 (VEI-8) eruption by the comparison of sulfur emission strength is found to be 5.3 (7) times higher than estimated from geological evidence. Throughout the investigated period, the frequency of volcanic eruptions is rather constant and comparable to that of recent times. During the deglacial period (16–9 ka b2k), however, there is a notable increase in the frequency of volcanic events recorded in Greenland and an obvious increase in the fraction of very large eruptions. For Antarctica, the deglacial period cannot be distinguished from other periods. These volcanoes documented in ice cores provide atmospheric sulfate burden and climate forcing for further research on climate impact and understanding the mechanism of the Earth system.

Optical properties of surface aerosols at Dome C, Antarctica in 2007–2013 and their potential source areas are presented. Scattering coefficients (σsp) were calculated from measured particle number size distributions with a Mie code and from filter samples using mass scattering efficiencies. Absorption coefficients (σap) were determined with a 3-wavelength Particle Soot Absorption Photometer (PSAP) and corrected for scattering by using two different algorithms. The scattering coefficients were also compared with σsp measured with a nephelometer at the South Pole Station (SPO). The minimum σap was observed in the austral autumn and the maximum in the austral spring, similar to other Antarctic sites. The darkest aerosol, i.e., the lowest single scattering albedo ωo ≈ 0.91 was observed in September and October and the highest ωo ≈ 0.99 in February and March. The uncertainty of the absorption Ångström exponent αap is high. The lowest αap monthly medians were observed in March and the highest in August–October. The equivalent black carbon (eBC) mass concentrations were compared with eBC measured at three other Antarctic sites: the SPO and two coastal sites, Neumayer and Syowa. The maximum monthly median eBC concentrations are almost the same (≈ 3 ± 1 ng m−3) at all these sites in October–November. This suggests that there is no significant difference in eBC between the coastal and plateau sites. The seasonal cycle of the eBC mass fraction exhibits a minimum f(eBC) ≈ 0.1 % in February–March and a maximum ≈ 4–5 % in August–October. Source areas were calculated using 50-day FLEXPART footprints. The highest eBC concentrations and the lowest ωo were associated with air masses coming from South America, Australia and Africa. Vertical simulations that take BC particle removal processes into account show that there would be essentially no BC particles arriving at Dome C from north of latitude 10° S at altitudes sp was similar to that observed at Dome C in the austral summer but there was a large difference in winter, suggesting that in winter SPO is more influenced by sea spray emissions than Dome C. The seasonal cycles of σsp at Dome C and at the SPO were compared with the seasonal cycles of secondary and primary marine aerosol emissions. The σsp measured at SPO correlated much better with the sea-spray aerosol emission fluxes in the Southern Ocean than σsp at Dome C. The seasonal cycles of biogenic secondary aerosols were estimated from monthly average phytoplankton biomass concentrations obtained from the CALIOP satellite sensor data. The analysis suggests that a large fraction of the biogenic scattering aerosol observed at Dome C has been formed in the polar zone but it may take a month for the aerosol to be formed, grown and get transported from the sea level to Dome C.

In this work, we present chemical stratigraphies of two sampling lines collected within a 4 m depth snow pit dug in Dome C during the Antarctic summer Campaign 2017/2018, 12 years after the last reported snow pit. The first sampling line was analyzed for nine anionic and cationic species using Ion Chromatography (IC), the second sampling line was analyzed for seven major elements in an innovative way with Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) after sample pre-concentration, allowing the study of deposition processes of new markers especially related to crustal source. This coupled analysis, besides confirming previous studies, allowed us to investigate the depositions of the last decades at Dome C, enriching the number of the detected chemical markers, and yielding these two techniques complementary for the study of different markers in this kind of matrix. As a result of the dating, the snow layers analyzed covered the last 50 years of snow depositions. The assessment of the accumulation rate, estimated about 9 cm yr−1, was accomplished only for the period 1992–2016, as the eruption of 1992 constituted the only tie-point found in nssSO42− depth profile. Na, the reliable sea salt marker, together with Mg and Sr, mainly arose from marine sources, whereas Ca, Al and Fe originated from crustal inputs. Post-depositional processes occurred on Cl− as well as on NO3− and methanesulfonic acid (MSA), compared to the latter, Cl− had a more gradual decrease, reporting a threshold at 2.5 m for the post-depositional process completion. For NO3− and MSA, instead, the threshold was shallower, at about 1 m depth, with a loss of 87% for NO3− and of 50% for MSA.

Ten years of data of biogenic aerosol (methane sulfonic acid, MSA, and non-sea salt sulfate, nssSO42−) collected at Concordia Station in the East Antarctic plateau (75° 06′ S, 123° 20′ E) are interpreted as a function of the Southern Annular Mode (SAM), Chlorophyll-a concentration (Chl-a; a proxy for phytoplankton biomass), sea ice extent and area. It is possible to draw three different scenarios that link these parameters in early, middle, and late summer. In early summer, the biogenic aerosol is significantly correlated to sea ice retreats through the phytoplankton biomass increases. Chl-a shows a significant correlation with nssSO42− in the finest fraction (< 1 μm). In contrast, only Chl-a in West Pacific and Indian Ocean sectors correlates with MSA in the coarse fraction. The transport routes towards the inner Antarctic plateau and aerosol formation processes could explain the different correlation patterns of the two compounds both resulting from the DMS oxidation. In mid-summer, Chl-a concentrations are at the maximum and are not related to sea ice melting. Due to the complexity of transport processes of air masses towards the Antarctic plateau, the MSA concentrations are low and not related to Chl-a concentration. In late summer, MSA and nssSO42− present the highest concentrations in their submicrometric aerosol fraction, and both are significantly correlated with Chl-a but not with the sea ice. In early and mid-summer, the enhanced efficiency of transport processes from all the surrounding oceanic sectors with air masses traveling at low elevation can explain the highest concentrations of nssSO42− and especially MSA. Finally, considering the entire time series, MSA shows significant year-to-year variability. This variability is significantly correlated with SAM but with a different time lag in early (0-month lag) and late summer (4-months lag). This correlation likely occurs through the effect of the SAM on phytoplankton blooms.

19 pages, 9 figures, 1 table, Aerosols are an integral part of the Arctic climate system due to their direct interaction with radiation and indirect interaction through cloud formation. Understanding aerosol size distributions and their dynamics is crucial for the ability to predict these climate relevant effects. When of favourable size and composition, both long-rangetransported-and locally formed particles-may serve as cloud condensation nuclei (CCN). Small changes of composition or size may have a large impact on the low CCN concentrations currently characteristic of the Arctic environment. We present a cluster analysis of particle size distributions (PSDs; size range 8-500 nm) simultaneously collected from three high Arctic sites during a 3-year period (2013-2015). Two sites are located in the Svalbard archipelago: Zeppelin research station (ZEP; 474 m above ground) and the nearby Gruvebadet Observatory (GRU; about 2 km distance from Zeppelin, 67 m above ground). The third site (Villum Research Station at Station Nord, VRS; 30 m above ground) is 600 km west-northwest of Zeppelin, at the tip of northeastern Greenland. The GRU site is included in an inter-site comparison for the first time. K-means cluster analysis provided eight specific aerosol categories, further combined into broad PSD classes with similar characteristics, namely pristine low concentrations (12 %-14 % occurrence), new particle formation (16 %-32 %), Aitken (21 %-35 %) and accumulation (20 %-50 %). Confined for longer time periods by consolidated pack sea ice regions, the Greenland site GRU shows PSDs with lower ultrafine-mode aerosol concentrations during summer but higher accumulation-mode aerosol concentrations during winter, relative to the Svalbard sites. By association with chemical composition and cloud condensation nuclei properties, further conclusions can be derived. Three distinct types of accumulation-mode aerosol are observed during winter months. These are associated with sea spray (largest detectable sizes, > 400 nm), Arctic haze (main mode at 150 nm) and aged accumulation-mode (main mode at 220 nm) aerosols. In contrast, locally produced particles, most likely of marine biogenic origin, exhibit size distributions dominated by the nucleation and Aitken mode during summer months. The obtained data and analysis point towards future studies, including apportioning the relative contribution of primary and secondary aerosol formation pro cesses and elucidating anthropogenic aerosol dynamics and transport and removal processes across the Greenland Sea. In order to address important research questions in the Arctic on scales beyond a singular station or measurement events, it is imperative to continue strengthening international scientific cooperation, This research has been supported by the Spanish Ministry of Economy through project BIO-NUC (CGL2013-49020-R), PI-ICE (CTM2017-89117-R) and the Ramon y Cajal fellowship (RYC-2012-11922). The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 654109, the Danish Council for Independent Research (project NUMEN, DFF-FTP-4005-00485B) and previously from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 262254. The work at Villum Research Station, Station Nord, was financially supported by the Danish Environmental Protection Agency via the MIKA/DANCEA funds for Environmental Support to the Arctic Region. The Villum Foundation funded the construction of Villum Research Station, Station Nord. CCN measurements are supported by a KOPRI program (PN19081), funded by a National Research Foundation of Korea grant (NRF-2016M1A5A1901769). The authors acknowledge financial support (to David C. S. Beddows) from the Natural Environment Research Council's funding of the National Centre for Atmospheric Science (NCAS) (grant number R8/H12/83/011)

This study investigated the elemental composition of PM10 collected in a polar environment (Ny-Alesund, Norwegian Arctic), to identify its sources and to understand the effects of short- and long-range transport processes. Natural (crustal and marine) and anthropogenic Arctic PM sources were identified, and specific emission sources were recognised by means of Principal Component Analysis and Hierarchical Cluster Analysis: airborne pollution deriving from ship fuels, local vehicle (non-exhaust) and continental emissions (e.g. incinerators or industries) were the main sources of anthropogenic elements. The results obtained so far from samples collected during four successive spring-summer sampling campaigns (2010–2013) show a remarkable seasonal trend for most of the investigated elements. For both geogenic and anthropogenic elements, concentrations are generally higher in March and April, when the ground is almost entirely covered by snow and ice, suggesting that long-range transport processes might be taking place. On the other hand, the concentrations of anthropogenic metals related to ship emissions (i.e. Co, Ni and V) peak in late spring and summer, when the marine traffic in the fjord is generally higher. For most of the analytes, the four campaigns were not significantly different; therefore, in the studied period, the composition of PM10 in Ny-Alesund did not vary remarkably. Finally, the behaviour of Rare Earth Elements was discussed in terms of parent material mineralogy.

A particulate matter (PM) source apportionment study was carried out in one of the most polluted districts of Tuscany (Italy), close to an old waste incinerator plant. Due to the high PM10 levels, an extensive field campaign was supported by the Regional Government to identify the main PM sources and quantify their contributions. PM10 daily samples were collected for one year and analysed by different techniques to obtain a complete chemical characterisation (elements, ions and carbon fractions). Hourly fine (2.5 μm) and coarse (2.5-10 μm) aerosol samples were collected by a Streaker sampler for a shorter period and hourly elemental concentrations were obtained by PIXE. Positive Matrix Factorization (PMF) analysis of daily and hourly data allowed the identification of 10 main sources: six anthropogenic (Biomass Burning, Traffic, Secondary Nitrates, Secondary Sulphates, Incinerator, Heavy Oil combustion), two natural (Saharan Dust and Fresh Sea Salt) and two mixed sources (Local Dust and Aged Sea Salt). Biomass burning turned out to be the main source of PM, accounting for 30% of the PM10 mass as annual average, followed by Traffic (18%) and Secondary Nitrates (14%). Emissions from the Incinerator turned out to be only 2% of PM10 mass on average. PM10 composition and source apportionment have been assessed in a polluted area near a waste incinerator, by PMF analysis on daily and hourly compositional data sets.

Ice core dating is the first step for a correct interpretation of climatic and environmental changes. In this work, we release a stratigraphic dating of the uppermost 197 m of the 250 m deep GV7(B) ice core (drilling site, 70°41’S, 158°52’E, 1950 m a.s.l.) with a sub-annual resolution. Chemical stratigraphies of NO3−, MSA (methanesulfonic acid), non-sea salt SO42−, sea-salt ions and the oxygen isotopic composition (δ18O) were used in the annual layer counting upon the identification of a seasonal profile in their records. Different procedures were tested and thanks to the volcanic history of the core, obtained in previous works, an accurate age-depth correlation was obtained for the period 1179–2009 CE. Once the dating of the core was finalized, the annual mean accumulation rate was evaluated throughout the analyzed 197 m of the core, obtaining an annually resolved history of the snow accumulation on site in the last millennium. A small, yet consistent, rise in accumulation rate was found for the last 830 years since the middle of the 18th century.

19 pages, 8 figures,1 table, 1 appendix.-- Data availability: The APS data can be accessed from https://doi.org/10.5281/zenodo.3961473 (Traversi et al., 2020). The absorption coefficient data are available upon request from Gilardoni et al. (2020). Data supporting this publication can be accessed upon request from the corresponding authors, Understanding aerosol–cloud–climate interactions in the Arctic is key to predicting the climate in this rapidly changing region. Whilst many studies have focused on submicrometer aerosol (diameter less than 1 µm), relatively little is known about the supermicrometer 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 during the study period (mainly from March to October) 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 %) is attributed 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- and long-distance origins and mixtures with Arctic haze, biogenic and likely blowing snow aerosols. Studying supermicrometer natural aerosol in the Arctic is imperative for understanding the impacts of changing natural processes on Arctic aeroso, This research has been supported by the Natural Environment Research Council (grant no. NE/S00579X/1). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Seasonal to interannual variations in the concentrations of sulfur aerosols (