Measurements of aerosol and CCN properties in the Mackenzie River delta (Arctic) during RACEPAC

Within the framework of the RACEPAC (Radiation-Aerosol-Cloud Experiment in the Arctic Circle) project, the Arctic aerosol, arriving at a ground-based station in Tuktoyaktuk (Mackenzie River delta area, Canada), was characterized during a period of 3 weeks in May 2014. Basic meteorological parameters and particle number size distributions (PNSDs) were observed and two distinct types of air masses were found. One type were typical Arctic haze air masses, termed accumulation-type air masses, characterized by a monomodal PNSD with a pronounced accumulation mode at sizes above 100 nm. These air masses were observed during a period when back trajectories indicate an air mass origin in the north-east of Canada. The other air mass type is characterized by a bimodal PNSD with a clear minimum around 90nm and with an Aitken mode consisting of freshly formed aerosol particles. Back trajectories indicate that these air masses, termed Aitken-type air masses, originated from the North Pacific. In addition, the application of the PSCF receptor model shows that air masses with their origin in active fire areas in central Canada and Siberia, in areas of industrial anthropogenic pollution (Norilsk and Prudhoe Bay Oil Field) and the north-west Pacific have enhanced total particle number concentrations (N[CN]). Generally, N[CN] ranged from 20 to 500 cm³, while cloud condensation nuclei (CCN) number concentrations were found to cover a range from less than 10 up to 250 cm³ for a supersaturation (SS) between 0.1 and 0.7 %. The hygroscopicity parameter kappa of the CCN was determined to be 0.23 on average and variations in kappa were largely attributed to measurement uncertainties.