Activity size distribution of 7Be in association with trace metals in the urban area of the city of Thessaloniki, Greece

The activity size distributions of the natural radionuclide tracer 7Be and associated trace metals 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 a typical traffic-affected urban site in the center of the city of Thessaloniki, Greece, over a seven month period (June’09–January’10). The activity median aerodynamic diameter (AMAD) ranged from 0.58 to 1.22 μm (avg 0.80 μm), indicating post-condensation growth either in the upper atmosphere or after mixing in the boundary layer. It was shown that more than 80% of the 7Be activity was associated with particles smaller than 1.3 μm. The AMAD values are anticorrelated with 7Be activities, while they are correlated with RH% with high confidence (R = 0.92, p < 0.00813). The composition of the associated particles is basically Ca, Si and S. Among the heavy metals determined, Fe is the most abundant, followed by Cu. Minor amounts of Pb, Cr, Ni are presented in coarse size ranges. The amount of Fe increased with decreasing particle size, displaying positive correlation with AMAD of 7Be in case of strong wind from NW direction and indicating the transport of pollutted air from the industrial area of the city of Thessaloniki. The measured distributions are believed to result from a combination of processes including local anthropogenic and natural sources, such as traffic, industrial emissions and resuspension of road dust. However, the local meteorological conditions seem to affect the final activity size distribution of 7Be and their associated trace element distributions.

Research highlights
► The Activity Median Aerodynamic Diameter (AMAD) of radioactive nuclide 7Be are anticorrelated with 7Be activities.
► The Activity Median Aerodynamic Diameter (AMAD) of radioactive nuclide 7Be are correlated with RH% with high confidence (R = 0.92, p < 0.00813).
► The activity size distribution of the radioactive nuclide 7Be seems that can be used as an index of air pollutant conditions.
► Under certain weather conditions 7Be presents similar behavior with some trace metals like Fe, Cu, in the urban area of a big city.