Potential genesis and implications of calcium nitrate in Antarctic snow

Abstract. Among the large variety of particulates in the atmosphere, calcic mineral dust particles have highly reactive surfaces that undergo heterogeneous reactions with atmospheric acids contiguously. The association between nssCa²⁺, an important proxy indicator of mineral dust, and NO₃⁻, a dominant anion in the Antarctic snowpack, was analysed. A total of 41 snow cores ( ∼  1 m each) that represent snow deposited during 2008–2009 were studied along coastal–inland transects from two different regions in East Antarctica – the Princess Elizabeth Land (PEL) and central Dronning Maud Land (cDML). Correlation statistics showed a strong association (at 99 % significance level) between NO₃⁻ and nssCa²⁺ at the near-coastal sections of both PEL (r  =  0.74) and cDML (r  =  0.82) transects. Similarly, a strong association between these ions was also observed in snow deposits at the inland sections of PEL (r  =  0.73) and cDML (r  =  0.84). Such systematic associations between nssCa²⁺ and NO₃⁻ are attributed to the interaction between calcic mineral dust and nitric acid in the atmosphere, leading to the formation of calcium nitrate (Ca(NO₃)₂) aerosol. Principal component analysis revealed common transport and depositional processes for nssCa²⁺ and NO₃⁻ both in PEL and cDML. Forward- and back-trajectory analyses using HYSPLIT model v. 4 revealed that southern South America (SSA) was an important dust-emitting source to the study region, aided by the westerlies. Particle size distribution showed that over 90 % of the dust was in the range  <  4 µm, indicating that these dust particles reached the Antarctic region via long-range transport from the SSA region. We propose that the association between nssCa²⁺ and NO₃⁻ occurs during the long-range transport due to the formation of Ca(NO₃)₂ rather than to local neutralisation processes. However, the influence of local dust sources from the nunataks in cDML and the contribution of high sea salt in coastal PEL evidently mask such association in the mountainous and coastal regions respectively. Ionic balance calculations showed that 70–75 % of NO₃⁻ in the coastal sections was associated with nssCa²⁺ (to form Ca(NO₃)₂). However, in the inland sections, 50–55 % of NO₃⁻ was present as HNO₃. The study indicates that the input of dust-bound NO₃⁻ contributes a significant fraction of the total NO₃⁻ deposited in coastal Antarctic snow.