This dataset contains particle number size distributions between 1.06-16.1 μm (aerodynamic diameter) and total concentration averaged to 1 min time resolution, measured with a commercial Aerodynamic Particle Sizer spectrometer (APS model 3321, TSI Incorporated, Minnesota, USA) during the year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition from October 2019 to September 2020. The measurements were performed in the Swiss container on the D-deck of Research Vessel Polarstern.