Variations of constituents of individual sea-salt particles at Syowa station, Antarctica

Abstract

Sampling of atmospheric aerosol particles was carried out at Syowa station, Antarctica (39.58°E, 69.00°S) in 1998. For a better understanding of sea-salt chemistry in the coastal Antarctic regions, individual sea-salt particles were analysed using a scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM-EDX). Individual particle analysis indicates that more sea-salt particles were modified in fine particles (0.2–2 µm in diameter) through heterogeneous reactions mainly with gaseous sulfur species in the summer and reactive nitrogen oxides in the winter—spring. In particular, sea-salt particles in the coastal Antarctic atmosphere may be modified by heterogeneous reactions with not only SO₂ and H₂SO₄ but also volatile sulfur species (e.g. CH₃SO₃H, DMS and DMSO) derived from bioactivity on the ocean surface during the summer. Also, low air temperature and a larger extent of sea ice offshore Syowa probably enhanced release of fractionated sea-salt particles (S-rich, Mg-rich, K-rich and Ca-rich) from the surface of snow and sea ice, particularly in September—October 1998. In addition, we attempt to estimate the scavenging rate of atmospheric sulfur species and reactive nitrogen oxides by dry deposition of sea-salt particles. Our estimation suggests that the upper limit of the scavenging rate of atmospheric sulfur species by sea-salt particles could rise to approximately 0.5 nmol m⁻2 day⁻1 at Syowa station during the summer. This value corresponded to about 30% of the concentration of particulate sulfur species such as non-sea-salt (nss)-SO²⁻₄ and CH₃SO⁻₃ and ~10% of total atmospheric sulfur species (nss-SO²⁻₄, CH₃SO⁻₃ and SO₂). In contrast, the estimated NO⁻₃ scavenging rate by sea-salt particles was ~0.2 nmol m⁻2 day⁻1, which is similar to the dry deposition rate of HNO₃+N₂O₅ (approximately 0.2–0.3 nmol m⁻2 day⁻1). Hence, sea-salt particles probably play an important role as scavengers of acidic species in the coastal Antarctic regions.