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Abstract Natural aerosols are an important, yet understudied, part of the Arctic climate system. Natural marine biogenic aerosol components (e.g., methanesulfonic acid, MSA) are becoming increasingly important due to changing environmental conditions. In this study, we combine in situ aerosol observations with atmospheric transport modeling and meteorological reanalysis data in a data-driven framework with the aim to (1) identify the seasonal cycles and source regions of MSA, (2) elucidate the relationships between MSA and atmospheric variables, and (3) project the response of MSA based on trends extrapolated from reanalysis variables and determine which variables are contributing to these projected changes. We have identified the main source areas of MSA to be the Atlantic and Pacific sectors of the Arctic. Using gradient-boosted trees, we were able to explain 84% of the variance and find that the most important variables for MSA are indirectly related to either the gas- or aqueous-phase oxidation of dimethyl sulfide (DMS): shortwave and longwave downwelling radiation, temperature, and low cloud cover. We project MSA to undergo a seasonal shift, with non-monotonic decreases in April/May and increases in June-September, over the next 50 years. Different variables in different months are driving these changes, highlighting the complexity of influences on this natural aerosol component. Although the response of MSA due to changing oceanic variables (sea surface temperature, DMS emissions, and sea ice) and precipitation remains to be seen, here we are able to show that MSA will likely undergo a seasonal shift solely due to changes in atmospheric variables. 

Abstract. Aerosol particles are an important part of the Earth climate system, and their concentrations are spatially and temporally heterogeneous, as well as being variable in size and composition. Particles can interact with incoming solar radiation and outgoing longwave radiation, change cloud properties, affect photochemistry, impact surface air quality, change the albedo of snow and ice, and modulate carbon dioxide uptake by the land and ocean. High particulate matter concentrations at the surface represent an important public health hazard. There are substantial data sets describing aerosol particles in the literature or in public health databases, but they have not been compiled for easy use by the climate and air quality modeling community. Here, we present a new compilation of PM2.5 and PM10 surface observations, including measurements of aerosol composition, focusing on the spatial variability across different observational stations. Climate modelers are constantly looking for multiple independent lines of evidence to verify their models, and in situ surface concentration measurements, taken at the level of human settlement, present a valuable source of information about aerosols and their human impacts complementarily to the column averages or integrals often retrieved from satellites. We demonstrate a method for comparing the data sets to outputs from global climate models that are the basis for projections of future climate and large-scale aerosol transport patterns that influence local air quality. Annual trends and seasonal cycles are discussed briefly and are included in the compilation. Overall, most of the planet or even the land fraction does not have sufficient observations of surface concentrations – and, especially, particle composition – to characterize and understand the current distribution of particles. Climate models without ammonium nitrate aerosols omit ∼ 10 % of the globally averaged surface concentration of aerosol particles in both PM2.5 and PM10 size fractions, with up to 50 % of the surface concentrations not being included in some regions. In these regions, climate model aerosol forcing projections are likely to be incorrect as they do not include important trends in short-lived climate forcers. 

Abstract. In this study, we present atmospheric ice-nucleating particle (INP)concentrations from the Gruvebadet (GVB) observatory in Ny-Ålesund(Svalbard). All aerosol particle sampling activities were conducted in April–August 2018. Ambient INP concentrations (nINP) were measured for aerosolparticles collected on filter samples by means of two offline instruments:the Dynamic Filter Processing Chamber (DFPC) and the West Texas CryogenicRefrigerator Applied to Freezing Test system (WT-CRAFT) to assesscondensation and immersion freezing, respectively. DFPC measured nINPs for aset of filters collected through two size-segregated inlets: one fortransmitting particulate matter of less than 1 µm (PM1), theother for particles with an aerodynamic diameter of less than 10 µmaerodynamic diameter (PM10). Overall, nINPPM10 measured by DFPC ata water saturation ratio of 1.02 ranged from 3 to 185 m−3 attemperatures (Ts) of −15 to −22 ∘C. On average, the super-micrometer INP (nINPPM10-nINPPM1) accounted forapproximately 20 %–30 % of nINPPM10 in spring, increasing in summer to45 % at −22 ∘C and 65 % at −15 ∘C. This increase in super-micrometer INP fraction towards summer suggests that super-micrometeraerosol particles play an important role as the source of INPs in theArctic. For the same T range, WT-CRAFT measured 1 to 199 m−3. Althoughthe two nINP datasets were in general agreement, a notable nINP offset wasobserved, particularly at −15 ∘C. Interestingly, the results ofboth DFPC and WT-CRAFT measurements did not show a sharp increase in nINPfrom spring to summer. While an increase was observed in a subset of ourdata (WT-CRAFT, between −18 and −21 ∘C), the spring-to-summernINP enhancement ratios never exceeded a factor of 3. More evident seasonal variability was found, however, in our activated fraction (AF) data, calculated by scaling the measured nINP to the total aerosol particleconcentration. In 2018, AF increased from spring to summer. This seasonal AFtrend corresponds to the overall decrease in aerosol concentration towardssummer and a concomitant increase in the contribution of super-micrometer particles. Indeed, the AF of coarse particles resulted markedly higher thanthat of sub-micrometer ones (2 orders of magnitude). Analysis of low-traveling back-trajectories and meteorological conditions at GVB matched to our INP data suggests that the summertime INP population isinfluenced by both terrestrial (snow-free land) and marine sources. Ourspatiotemporal analyses of satellite-retrieved chlorophyll a, as well as spatial source attribution, indicate that the maritime INPs at GVB may comefrom the seawaters surrounding the Svalbard archipelago and/or in proximityto Greenland and Iceland during the observation period. Nevertheless,further analyses, performed on larger datasets, would be necessary to reachfirmer and more general conclusions.