Ice-nucleating particle concentration measurements from Ny-Ålesund during the Arctic spring–summer in 2018

Abstract. In this study, we present atmospheric ice-nucleating particle (INP) concentrations from the Gruvebadet (GVB) observatory in Ny-Alesund (Svalbard). All aerosol particle sampling activities were conducted in April–August 2018. Ambient INP concentrations ( n INP) were measured for aerosol particles collected on filter samples by means of two offline instruments: the Dynamic Filter Processing Chamber (DFPC) and the West Texas Cryogenic Refrigerator Applied to Freezing Test system (WT-CRAFT) to assess condensation and immersion freezing, respectively. DFPC measured n INPs for a set of filters collected through two size-segregated inlets: one for transmitting particulate matter of less than 1  µm (PM 1 ), the other for particles with an aerodynamic diameter of less than 10  µm aerodynamic diameter (PM 10 ). Overall, n INP PM 10 measured by DFPC at a water saturation ratio of 1.02 ranged from 3 to 185 m −3 at temperatures ( T s) of −15 to −22 ∘ C. On average, the super-micrometer INP ( n INP PM 10 - n INP PM 1 ) accounted for approximately 20 %–30 % of n INP PM 10 in spring, increasing in summer to 45 % at −22 ∘ C and 65 % at −15 ∘ C. This increase in super-micrometer INP fraction towards summer suggests that super-micrometer aerosol particles play an important role as the source of INPs in the Arctic. For the same T range, WT-CRAFT measured 1 to 199 m −3 . Although the two n INP datasets were in general agreement, a notable n INP offset was observed, particularly at −15 ∘ C. Interestingly, the results of both DFPC and WT-CRAFT measurements did not show a sharp increase in n INP from spring to summer. While an increase was observed in a subset of our data (WT-CRAFT, between −18 and −21 ∘ C), the spring-to-summer n INP 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 n INP to the total aerosol particle concentration. In 2018, AF increased from spring to summer. This seasonal AF trend corresponds to the overall decrease in aerosol concentration towards summer and a concomitant increase in the contribution of super-micrometer particles. Indeed, the AF of coarse particles resulted markedly higher than that 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 is influenced by both terrestrial (snow-free land) and marine sources. Our spatiotemporal analyses of satellite-retrieved chlorophyll  a , as well as spatial source attribution, indicate that the maritime INPs at GVB may come from the seawaters surrounding the Svalbard archipelago and/or in proximity to Greenland and Iceland during the observation period. Nevertheless, further analyses, performed on larger datasets, would be necessary to reach firmer and more general conclusions.