Blowing snow at coastal Antarctica: a source of ions and sodium chloride clusters

Abstract. Strong winds accompanied with flying snow produce high concentrations of air ions and small ion clusters. The physical production mechanisms and the chemical nature of those clusters have remained an open question. We measured the ion cluster concentration and their chemical composition at Neumayer III station in Queen Maud land, Antarctica, during a 3-month measurement campaign from Nov 2018 – Feb 2019.  We found that negative ion clusters are mostly composed of sodium chloride (NaCl). The chloride (Cl^- -ion) was the most abundant core ion and charge carrier in the observed clusters.  Other identified core ions included MnO^-, I^-, IO₃^-, NaO^-, NaO₂^-, SO₃^-, HSO₄^-, NO₃^-, O₂^-, CaCl^-and HS^-. The concentration of 0.8–2 nm ion clusters during blizzards were 30-fold compared to fair weather conditions, reaching 10⁴ cm^-3 with wind speeds exceeding 18 m s^-1. Our observations are important for a comprehensive understanding of ionization and ion cluster production in Antarctica’s atmosphere. Negative ion induced nucleation of sulfuric acid and ammonia is the main new particle formation mechanism in Antarctica and the nucleation rate is dependent on ion concentration. Snowstorms and ions produced within the blizzard could serve as an additional source of ions for subsequent new particle and eventually cloud condensation nuclei production.