Distributions of water-soluble ions in size-aggregated aerosols over the Southern Ocean and coastal Antarctica

Abstract

To investigate mass size distributions of water-soluble ions in aerosols in the marine boundary layer (MBL) over the Southern Ocean, size-segregated (0.056–18 μm in aerodynamic diameter) aerosols were collected on the 28^th Chinese National Antarctic Research Expedition (CHINARE) cruise from November 2011 to March 2012. Major water-soluble inorganic and organic species in aerosols were analyzed by ion chromatography (IC). Results showed that high loadings of aerosol mass were observed over the western sector of the Southern Ocean, attributed to the high mass loadings of Na⁺ and Cl⁻ in the particles >1.0 μm in diameter and high mass loadings of non-sea-salt (nss) SO₄²⁻ and methanesulfonate (MSA) in the particles <1.0 μm in diameter. Nss-SO₄²⁻ and MSA accounted for ∼40% of the total mass in aerosols with particle size <0.56 μm over the eastern sector of the Southern Ocean, while it was elevated to more than 60% over the western sector of the Southern Ocean that could be linked with high marine productivity reflected by high chlorophyll-a occurrence in surface waters in that region. MSA/nss-SO₄²⁻ ratios showed an increasing trend as latitude increased in the southern hemisphere with a dramatic increase south of 60 °S and the variation of MSA may shape the spatial distribution of the ratios. High MSA concentration and MSA/nss-SO₄²⁻ ratios were observed in west Antarctica, especially in the supermicron particles. A bimodal mass size distribution of total Ca²⁺ with a small peak in the 0.18–0.32 μm size range was observed, suggesting different sea spray aerosol (SSA) production mechanisms. Nss-SO₄²⁻, MSA was mainly enriched in the particle size range of 0.18 μm to 0.56 μm. The concentrations of formate and oxalate were low and detected only in certain size particles, mainly in the range <0.56–1.8 μm. Further studies should be conducted over the remote Southern Ocean to reveal marine ecosystem–aerosol–climate interactions.