ASCOS was an interdisciplinary expedition to the central Arctic on the icebreaker Oden from 1 August to 9 September 2008. The expedition focused on processes relating to cloud formation in the summer Arctic and included observations of marine biology and chemistry, atmospheric chemistry, physical oceanography, aerosol chemistry and physics, and meteorology. These measurements were made by a time-of-flight aerosol mass spectrometer (C-ToF AMS) and includes the chemical components of the aerosol that vapourized at 873 K (organic, sulphate, nitrate and methane sulphonate). Measurements were made every 5 minutes from a PM10 inlet 27 m above sea level and included a 20 day drift period around N87 W5. Values are reported in micrograms / standard cubic metre.