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

摘要

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.