Chemical forms of aerosol particles in Dome Fuji ice core for past 720 thousand years

Antarctic ice cores preserve records of past atmospheric solid aerosols as microparticles, providing useful information about past atmospheric environments. Dome Fuji ice core in Antarctica (77˚ 19' S, 39˚ 42' E, 3810 m a.s.l.) indicates these records over the past 720 thousand years. Such aerosols are transported from continent or sea as primary aerosols, and are also reacted them in atmosphere during their transportation as secondary aerosols. The chemical forms of micro inclusions in glacial and interglacial ice are different (Ohno et al., 2005). However, there is no such analysis over the past 720 thousand years. Here we present chemical forms of nonvolatile salts of aerosol particles in the Dome Fuji ice core by sublimation method, which can collect more than several hundred particles on a metal plate from 10g of ice sample (e.g. Iizuka et al., 2009). We selected 14 ice samples from a particularly warm and cold stages during glacial-interglacial cycles from Marine Isotope Stage (MIS) 16 to Holocene (MIS 1). In preparation, ice samples were sublimated by drawing clean air by a vacuum pomp in a clean booth at -20 °C though 50 hours. We used Micro-Raman spectroscopy (Jobin-Yvon, T64000) and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) (JSM-6360LV and JED2201) to identify the chemical form. As a result, NaCl is preserved more in glacial ice than in interglacial ice by SEM-EDS. Also, Na₂SO₄ is abundant in interglacial ice, while NaNO₃ is abundant in glacial ice by Micro-Raman spectroscopy. These sodium salts are considered as secondary aerosols by the reaction of sea-salt (NaCl) with sulfate and nitrate acid (H₂SO₄ and HNO₃). In interglacial periods, most of NaCl may react with H₂SO₄. Even if once NaNO₃ were formed, the equilibrium reaction of 2NaNO₃ + H₂SO₄ ⇄ Na₂SO₄ + 2HNO₃ moved to rightward by HNO₃ volatilization (Iizuka et al., 2016). In glacial periods, the amount of Na⁺ and Ca²⁺ fluxes have increased, while that of SO₄²- flux have not changed. Thus, it is considered that the most of H₂SO₄ reacted with them, and then NaNO₃ existed by reaction of HNO₃ and remained sea-salt.