Long-Term Trends of Lead-210 Concentrations in the Ground-Level Air in Finland and Bulgaria

Long-term records of airborne lead-210 should reveal periodic changes in the atmosphere, such as the North Atlantic Oscillation, as well as any systematic trends in large-scale weather phenomena transporting arctic, maritime or continental air masses which might be indications of a changing climate. The results of collaborative research on these matters show that starting from the mid-1980s, there has been a continuous decrease in average lead-210 contents in the ground-level air both in Finland and in Bulgaria. However, the decreasing trend is much stronger in Bulgaria compared to Finland. This trend may indicate that the climate is becoming more maritime in both northeastern and southeastern Europe, but that the effect is much stronger in the southeast of the continent. Because the sources of air masses are not the only factor determining lead-210 content in the air, the effect of precipitation causing wet deposition of lead-210 must be studied, too, as changes in precipitation amounts can influence the average residence time of lead-210 in the air.