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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 10 Oct 2019

Submitted as: research article | 10 Oct 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

On the annual variability of Antarctic aerosol size distributions at Halley research station

Thomas Lachlan-Cope1, David Beddows2, Neil Brough1, Anna E. Jones1, Roy M. Harrison2,a, Angelo Lupi3, Young Jun Yoon4, Aki Virkkula5,6, and Manuel Dall'Osto7 Thomas Lachlan-Cope et al.
  • 1British Antarctic Survey, NERC, High Cross, Madingley Rd, Cambridge, CB3 0ET, UK
  • 2National Center for Atmospheric Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
  • 3Institute of Atmospheric Sciences and Climate (ISAC), National Research Council (CNR), via P. Gobetti 101, 40129, Bologna, Italy
  • 4Korea Polar Research Institute, 26, Songdo Mirae-ro, Yeonsu-Gu, Incheon, KOREA 406-840
  • 5Institute for Atmospheric and Earth System Research, University of Helsinki, Helsinki, FI-00014, Finland
  • 6Finnish Meteorological Institute, FI-00101 Helsinki, Finland
  • 7Institute of Marine Sciences, Passeig Marítim de la Barceloneta, 37-49, E-08003, Barcelona, Spain
  • aalso at: Department of Environmental Sciences/Centre of Excellence in Environmental Studies, King Abdulaziz University, P.O. Box 80203, Jeddah, 21589, Saudi Arabia

Abstract. The Southern Ocean and Antarctic region currently best represent one of the few places left on our planet with conditions similar to the preindustrial age. Currently, climate models have low ability to simulate conditions forming the aerosol baseline; a major uncertainty comes from the lack of understanding of aerosol size distributions and their dynamics. Contrasting studies stress that primary sea-salt aerosol can contribute significantly to the aerosol population, challenging the concept of climate biogenic regulation by new particle formation (NPF) from dimethyl sulphide marine emissions.

We present a statistical cluster analysis of the physical characteristics of particle size distributions (PSD) collected at Halley (Antarctica) for the year 2015 (89 % data coverage). By applying the Hartigan-Wong k-Means method we find 8 clusters describing the entire aerosol population. Three clusters show pristine average low particle number concentrations (< 121–179 cm−3) with three main modes (30 nm, 75–95 nm, 135–160 nm) and represent 57 % of the annual PSD (up to 89–100 % during winter, 34–65 % during summer based upon monthly averages). Nucleation and Aitken mode PSD clusters dominate summer months (Sep–Jan, 59–90 %), whereas a clear bimodal distribution (43 and 134 nm, respectively, min Hoppel mode 75 nm) is seen only during the Dec–Apr period (6–21 %). Major findings of the current work include: (1) NPF and growth events originate from both the sea ice marginal zone and the Antarctic plateau, strongly suggesting multiple vertical origins, including marine boundary layer and free troposphere; (2) very low particle number concentrations are detected for a substantial part of the year (57 %), including summer (34–65 %), suggesting that the strong annual aerosol concentration cycle is driven by a short temporal interval of strong NPF events; (3) a unique pristine aerosol cluster is seen with a bimodal size distribution (75 nm and 160 nm, respectively), strongly correlating with wind speed and possibly associated with blowing snow and sea spray sea salt, dominating the winter aerosol population (34–54 %). A brief comparison with two other stations (Dome C Concordia and King Sejong Station) during the year 2015 (240 days overlap) shows that the dynamics of aerosol number concentrations and distributions are more complex than the simple sulphate-sea spray binary combination, and it is likely that an array of additional chemical components and processes drive the aerosol population. A conceptual illustration is proposed indicating the various atmospheric processes related to the Antarctic aerosols, with particular emphasis on the origin of new particle formation and growth.

Thomas Lachlan-Cope et al.
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Short summary
We present a statistical cluster analysis of the physical characteristics of particle size distributions collected at Halley (Antarctica) for the year 2015. Complex interactions between multiple ecosystems, coupled with different atmospheric circulation, result in very different aerosol size distributions populating the Southern Hemisphere.
We present a statistical cluster analysis of the physical characteristics of particle size...