Circum-Antarctic abundance and properties of CCN and INPs

• Published in: Atmospheric Chemistry and Physics
• Main Authors: C. Tatzelt, S. Henning, A. Welti, A. Baccarini, M. Hartmann, M. Gysel-Beer, M. van Pinxteren, R. L. Modini, J. Schmale, F. Stratmann
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; Southern Ocean; The Antarctic; Austral; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/acp-22-9721-2022; https://doaj.org/article/83169902ab9749729e9f3fb969d90529

Aerosol particles acting as cloud condensation nuclei (CCN) or ice-nucleating particles (INPs) play a major role in the formation and glaciation of clouds. Thereby they exert a strong impact on the radiation budget of the Earth. Data on abundance and properties of both types of particles are sparse, especially for remote areas of the world, such as the Southern Ocean (SO). In this work, we present unique results from ship-borne aerosol-particle-related in situ measurements and filter sampling in the SO region, carried out during the Antarctic Circumnavigation Expedition (ACE) in the austral summer of 2016–2017. An overview of CCN and INP concentrations over the Southern Ocean is provided and, using additional quantities, insights regarding possible CCN and INP sources and origins are presented. CCN number concentrations spanned 2 orders of magnitude, e.g. for a supersaturation of 0.3 % values ranged roughly from 3 to 590 cm −3 . CCN showed variable contributions of organic and inorganic material (inter-quartile range of hygroscopicity parameter κ from 0.2 to 0.9 ). No distinct size dependence of κ was apparent, indicating homogeneous composition across sizes (critical dry diameter on average between 30 and 110 nm ). The contribution of sea spray aerosol (SSA) to the CCN number concentration was on average small. Ambient INP number concentrations were measured in the temperature range from −5 to −27 ∘ C using an immersion freezing method. Concentrations spanned up to 3 orders of magnitude, e.g. at −16 ∘ C from 0.2 to 100 m −3 . Elevated values (above 10 m −3 at −16 ∘ C) were measured when the research vessel was in the vicinity of land (excluding Antarctica), with lower and more constant concentrations when at sea. This, along with results of backward-trajectory analyses, hints towards terrestrial and/or coastal INP sources being dominant close to ice-free (non-Antarctic) land. In pristine marine areas INPs may originate from both oceanic sources and/or long-range transport. Sampled aerosol particles (PM 10 ) ...