7Be aerosols in the Arctic atmosphere - modelling of air mass trajectories

The activity size distributions of the natural radionuclide tracer ⁷Be in different inhalable fractions (<;0.39 μm, 0.391-0.69 μm, 0.69-1.3 μm, 1.3-2.1 μm, 2.1-4.2 μm, 4.2-10.2 μm and >;10.2 μm) were determined in the boreal atmosphere in the Arctic Research Centre of the Finnish Meteorological Institute (FMI) at Sodankylä, Finland (67°22´ N, 26°38´ E, 180m asl). The activity median aerodynamic diameter (AMAD) ranged from 0.54 μm to 1.05 μm. More than 75% of the ⁷Be activity was found to be associated with particles smaller than 1.3 μm. An anticorrelation was observed between the AMAD values and ⁷Be activities. The observed correlation between the AMAD values and RH% can be due to the intense condensation process during high RH% conditions resulting in increased particle sizes. But this associated with possibly higher scavenging rates of aerosols does not necessarily alone explain the anticorrelation between the AMAD and the ⁷Be activities. The air mass origin associated with synoptic scale weather phenomena may contribute to that too. To study this an analysis of air mass back-trajectories was performed.