Morphological features and mixing states of soot-containing particles in the marine boundary layer over the Indian and Southern oceans

• Published in: Atmospheric Chemistry and Physics
• Main Authors: S. Ueda, K. Osada, K. Hara, M. Yabuki, F. Hashihama, J. Kanda
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; Southern Ocean; The Antarctic; Indian; Antarc*
• Online Access: https://doi.org/10.5194/acp-18-9207-2018; https://doaj.org/article/a5c54ef44701472f9ac2d3888e51f5c2

Mixing states of soot-containing aerosol particles constitute important information for the simulation of climatic effects of black carbon in the atmosphere. To elucidate the mixing states and morphological features of soot-containing particles over remote oceans, we conducted on-board observations over the southern Indian Ocean and the Southern Ocean during the TR/V Umitaka-maru UM-08-09 cruise, which started from Benoa, Indonesia, on 1 December 2008 via Cape Town, South Africa, and which terminated in Fremantle, Australia, on 6 February 2009. The light absorption coefficients of size-segregated particles ( < 0.5 and < 1.0 µm diameter) and aerosol number concentrations (0.1–0.5 µm diameter) were measured to assist direct aerosol sampling. Size-segregated aerosol particles were collected for chemical analysis using ion chromatography. For transmission electron microscopy (TEM) analyses using water-dialysis methods, dried submicrometer aerosol particles were collected using a cascade impactor. We analyzed 13 TEM samples. Results of water-dialysis analysis demonstrate that most particles were water-soluble. However, for all TEM samples, particles were rarely found (2.1 % of particles on a TEM sample at a maximum) containing insoluble residuals with the characteristic soot shape. For samples collected over the Indian and Southern oceans at latitudes less than 62° S, some (20–35 %) soot-containing particles were found as bare soot. For samples collected near the Antarctic coast (65–68° S, 38–68° E), all soot-containing particles were mixed with water-soluble materials. Furthermore, 56 % of soot-containing particles had a satellite structure formed by the impact of droplets such as sulfuric acid. Chemical analysis of submicrometer particles near the Antarctic coast revealed high concentrations of non-sea-salt (nss) SO 4 2− and CH 3 SO 3 − , suggesting that aged soot-containing particles were transformed by soluble materials derived from dimethyl sulfide (DMS) oxidation. The obtained information of soot at ...