10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Aerosol Particle Size Distributions and Compositions over the Southern Ocean in the Austral Summer of 2017
TAKUMA MIYAKAWA, Fumikazu Taketani, Masayuki Takigawa, Chunmao Zhu, Kazuhiko Matsumoto, Yutaka Tobo, Momoka Yoshizue, Yugo Kanaya, Japan Agency for Marine-Earth Science and Technology
Abstract Number: 722 Working Group: Remote/Regional Atmospheric Aerosol
Abstract Aerosol particles in the marine boundary layer are emitted from the ocean surface through the sea-spraying process. They can affect the cloud formation over the ocean, resulting in their significance in the Earth’s radiative budget, because the ocean aerial coverage is high on the earth. Southern Ocean (SO) is a unique region with rich ecosystems and without anthropogenic and continental natural impacts especially in austral summer (e.g., McCoy et al., 2015). To the best of our knowledge, the measurements of aerosol particles over the Pacific Ocean sector of SO are sparse and critically needed for understanding the concentration levels of aerosols to assess the role of aerosols as cloud condensation nuclei (CCN) in this region.
We have conducted ship-borne aerosol measurements using our research vessel “Mirai” in a framework of the research cruise “Trans South Pacific Project” between Japan and Chili (December 27, 2016-March 28, 2017). This cruise consisted 4 legs. RV "Mirai" was deployed over the SO (from Punta Arenas, CHL to Auckland, NZ) during the third leg in the late austral summer of 2017 (February 10-March 3, 2017). We have performed in-situ measurements of size distributions of total and non-volatile (at 300ºC) aerosol particles using a scanning mobility particle sizer (SMPS, TSI, the combination of a differential mobility analyzer model 3080 and a condensation particle counter model 3010), black carbon aerosol using a single particle soot photometer (SP2, DMT), and fluorescent bioaerosol particle (FBAP) using a wideband integrated bioaerosol sensor (WIBS4A, DMT) on the experimental room located on the upper level of RV Mirai. In the third leg, we performed air sampling for the post analyses of chemical composition, morphology (microscopy), and ice nucleating particles.
During the cruise of third leg, air masses without continental impacts were successfully observed except selected periods. We here assume the major source of aerosols in the MBL is the surface of the SO. Our observation results indicated that aerosol particles had the bimodal size distributions over the SO, which is commonly found in the MBL in a plenty of previous studies (e.g., Hoppel et al., 1990). The minimum diameter among two modes, so called Hoppel minimum (DHO), was around 70 nm on average, which can be used for estimating the supersaturation SS level in the cloud process with the assumed chemical composition (Hoppel et al., 1986). The estimated value of SS varied from 0.2-0.4% with the assumption of pure ammonium sulfate during the cruise. We will present the temporal variations of size-segregated aerosol concentrations, CCN-proxy (particles larger than DHO, e.g., Clarke and Kapustin, 2010), volume-fraction-remaining (VFR) at 300ºC as a diagnosis of the sea-salt particle impacts, FBAP, and the chemical composition (organic carbon) to elucidate the atmospheric physics and chemistry of natural aerosols in this region.
[1] Clarke and Kapustion (2010), Science, 329, 1488, doi:10.1126/science.1188838. [2] Hoppel et al. (1986), Geophys. Res. Lett., 13, 125–128, doi:10.1029/GL013i002p00125. [3] Hoppel et al. (1990), J. Geophys. Res., 95(D4), 3659–3686, doi:10.1029/JD095iD04p03659. [4] McCoy et al. (2015), Sci. Adv., doi:10.1126/sciadv.1500157.