The BACSAM II aircraft campaign, conducted with the polar research aircraft Polar 6 and the towed body T-Bird, took place from 3 April to 2 May 2024. It was based in Longyearbyen, Svalbard. In total, 11 low-level research flights and two transit flights were conducted, covering the region around Svalbard and north of Greenland.The data sets present aerosol number concentrations in the size range of 7-2000 nm measured with the advanced Mixing Condensation Particle Counter (aMCPC). The concentrations are provided for ambient conditions as well as reduced to standard temperature and pressure (STP). Additional parameters include GPS position, flow rate, and inlet temperature and pressure. Note that during the BACSAM II campaign, the aMCPC experienced some problems with its butanol supply, and thus the number concentration tends to be underestimated.