On the annual variability of Antarctic aerosol size distributions at Halley Research Station

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Lachlan-Cope, Thomas, Beddows, David C. S., Brough, Neil, Jones, Anna E., Harrison, Roy M., Lupi, Angelo, Yoon, Young Jun, Virkkula, Aki, Dall'Osto, Manuel
• Other Authors: Institute for Atmospheric and Earth System Research (INAR)
• Format: Article in Journal/Newspaper
• Language: English
• Published: COPERNICUS GESELLSCHAFT MBH 2021
• Subjects: 114 Physical sciences; Aitken; Antarctic; Halley Research Station; Hartigan; Southern Ocean; The Antarctic; Antarc*; Antarctica; Sea ice
• Online Access: http://hdl.handle.net/10138/326163

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 a 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 sulfide marine emissions. We present a statistical cluster analysis of the physical characteristics of particle size distributions (PSDs) collected at Halley (Antarctica) for the year 2015 (89 % data coverage; 6-209 nm size range; daily size resolution). By applying the Hartigan-Wong k-mean method we find eight clusters describing the entire aerosol population. Three clusters show pristine average low particle number concentrations (<121-179 cm(-3)) with three main modes (30, 75-95 and 135-160 nm) and represent 57 % of the annual PSD (up to 89 %-100 % during winter and 34 %-65 % during summer based on monthly averages). Nucleation and Aitken mode PSD clusters dominate summer months (SeptemberJanuary, 59 %-90 %), whereas a clear bimodal distribution (43 and 134 nm, respectively; Hoppel minimum at mode 75 nm) is seen only during the December-April 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 the 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 and 160 ...