The ultrafine particle (UFP) concentration is the concentration of particles having a diameter between 2.5 and 15 nm, it is reported in terms of particle number per cubic centimeter at a time resolution of 10 minutes. UFP are the smallest particles within the aerosol population and are formed from condensation of gaseous precursors (e.g., sulfuric acid or iodic acid). A high concentration of UFP is an indication that a new particle formation event is taking place or happened recently. Measurements were performed on the 4th deck of icebreaker Oden during August and September 2018 along the track of the Arctic Ocean 2018 expedition.