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.