Condensation and immersion freezing Ice Nucleating Particle measurements at Ny-Ålesund (Svalbard) during 2018: evidence of multiple source contribution

• Main Authors: Rinaldi, Matteo, Hiranuma, Naruki, Santachiara, Gianni, Mazzola, Mauro, Mansour, Karam, Paglione, Marco, Rodriguez, Cheyanne A., Traversi, Rita, Becagli, Silvia, Cappelletti, David M., Belosi, Franco
• Format: Text
• Language: English
• Published: 2020
• Subjects: Arctic; Greenland; Ny-Ålesund; Svalbard; Svalbard Archipelago; Iceland; Ny Ålesund
• Online Access: https://doi.org/10.5194/acp-2020-605; https://www.atmos-chem-phys-discuss.net/acp-2020-605/

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.