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<p>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 <span class="inline-formula">0.3</span> <span class="inline-formula">%</span> values ranged roughly from <span class="inline-formula">3</span> to <span class="inline-formula">590</span> <span class="inline-formula">cm⁻³</span>. CCN showed variable contributions of organic and inorganic material (inter-quartile range of hygroscopicity parameter <span class="inline-formula"><i>κ</i></span> from <span class="inline-formula">0.2</span> to <span class="inline-formula">0.9</span>). No distinct size dependence of <span class="inline-formula"><i>κ</i></span> was apparent, indicating homogeneous composition across sizes (critical dry diameter on average between <span class="inline-formula">30</span> and <span class="inline-formula">110</span> <span class="inline-formula">nm</span>). 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 <span class="inline-formula">−5</span> to <span class="inline-formula">−27</span> <span class="inline-formula">^∘</span>C using an immersion freezing method. Concentrations spanned up to 3 orders of magnitude, e.g. at <span class="inline-formula">−16</span> <span class="inline-formula">^∘</span>C from <span class="inline-formula">0.2</span> to <span class="inline-formula">100</span> <span class="inline-formula">m⁻³</span>. Elevated values (above <span class="inline-formula">10</span> <span class="inline-formula">m⁻³</span> at <span class="inline-formula">−16</span> <span class="inline-formula">^∘</span>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<span class="inline-formula">₁₀</span>) were analysed for sodium and methanesulfonic acid (MSA). Resulting mass concentrations were used as tracers for primary marine and secondary aerosol particles, respectively. Sodium, with an average mass concentration around <span class="inline-formula">2.8</span> <span class="inline-formula">µg m⁻³</span>, was found to dominate the sampled, identified particle mass. MSA was highly variable over the SO, with mass concentrations up to <span class="inline-formula">0.5</span> <span class="inline-formula">µg m⁻³</span> near the sea ice edge. A correlation analysis yielded strong correlations between sodium mass concentration and particle number concentration in the coarse mode, unsurprisingly indicating a significant contribution of SSA to that mode. CCN number concentration was highly correlated with the number concentration of Aitken and accumulation mode particles. This, together with a lack of correlation between sodium mass and Aitken and accumulation mode number concentrations, underlines the important contribution of non-SSA, probably secondarily formed particles, to the CCN population. INP number concentrations did not significantly correlate with any other measured aerosol physico-chemical parameter.</p>