Horizontal distributions of aerosol constituents and their mixing states in Antarctica during the JASE traverse

Abstract

Abstract. Measurements of aerosol number concentrations and direct aerosol sampling were conducted on continental Antarctica during the traverse of the Japanese-Swedish joint Antarctic expedition (JASE) from 14 November 2007 until 24 January 2008. Aerosol concentrations in background conditions decreased gradually with latitude in inland regions during the traverse. The lowest aerosol number concentrations were 160 L −1 in D p > 0.3 µm, and 0.5 L −1 in D p > 2 µm. In contrast, aerosol concentrations reached 3278 L −1 in D p > 0.3 µm, and 215 L −1 in D p > 2 µm under strong wind conditions. The estimated aerosol mass concentrations were 0.04-5.7 µg m −3 . Single particle analysis of aerosol particles collected during the JASE traverse was conducted using a scanning electron microscope equipped with an energy dispersive x ray spectrometer. Major aerosol constituents were sulfates in fine mode, and sulfate, sea salts, modified sea salts, and fractionated sea salts in coarse mode. K-rich sulfates, Mg-rich sulfate, Ca-rich sulfates, and minerals were identified as minor aerosol constituents. Horizontal features of Cl / Na ratios imply that sea-salt modification (i.e. Cl loss) occurred on the Antarctic continent during the summer. Most sea-salt particles in the continental region near the coast were modified with acidic sulfur species such as H 2 SO 4 and CH 3 SO 3 H. By contrast, acidic species other than the acidic sulfur species (likely HNO 3 ) contributed markedly to sea-salt modification in inland areas during the traverse. Mg-rich sea-salt particles and Mg-free sea-salt particles were present in coarse and fine modes from the coast to inland areas. These sea-salt particles might be associated with sea-salt fractionation on the snow surface of continental Antarctica.

Spatial distributions of soluble salts in surface snow of East Antarctica

“…Also, the major ions are consistent with the major salts NaCl, Na 2 SO 4 and NaNO 3 . The results are also consistent with Hara et al (2014), who seldom found ammonium salts, instead found that some of the major aerosol compositions on the same traverse route are Na 2 SO 4 and NaNO 3 . NaNO 3 is thought to be formed by (Kerminen et al, 2000) NaCl þ HNO 3 !…”

“…The scatter in these ternary diagrams exceeds that from previous aerosol analyses on the same traverse route (Hara et al, 2014). Since only a limited number of particles are actually used for EDS, sample heterogeneity may have contributed to the observed scatter.…”

“…A similar assumption is also adapted for atmospheric aerosols (e.g. Hara et al, 2014). If S (or Cl) is found in particles without Na, Mg or Ca, we regard the S-(or Cl-containing particles as other, unidentified sulphate (or chloride) salts.…”

“…Nevertheless, the sea-salt particles in snow may react with acid (HNO 3 or H 2 SO 4 ) and retain the same Cl ( /Na ' ratio. According to Hara et al (2014), atmospheric aerosols mainly consist of sea salt in spring and mainly modified sea salt in summer. As the snow was sampled in late November (late spring), there are two possible reasons for the springÁsummer difference.…”

“…To better understand the origins of these constituents and the chemical reactions that occur on aerosol particles, single-particle analyses of Antarctic aerosols have been done (Parungo et al, 1979;Artaxo et al, 1992;Hara et al, 1995Hara et al, , 2005Hara et al, , 2013Mouri et al, 1999). More recently, Hara et al (2014) showed that most sea-salt particles in the continental region near the coast were modified with acidic sulphur species such as H 2 SO 4 and CH 3 SO 3 H. In contrast, other, non-sulphurous acidic species (likely HNO 3 ) contributed markedly to sea-salt modification in inland areas during the traverse. The same ions (SO , allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.…”