Beryllium Isotopes In Aerosols Over Sweden

In this paper we present data on the distribution of Be-7 and Be-10 in aerosols sampled at ground level station in central Sweden during the period 1972-2005. The data indicate strong coherence between the distribution patterns of the two isotopes that is manifested by seasonal variability. Peaks with about 2-3 times higher concentrations than the mean annual average are observed during spring-summer seasons. The seasonal signal found in isotopic record suggests also influence of climatologic factors (precipitation, temperature and wind direction) together with imprints from changes in atmospheric production. The relatively high concentrations during the warm spring-summer seasons can be traced to continental, generally dry, air masses from high-pressure regions (such as Europe and central Asia) that can be associated with anticyclonic events, which provide more Be-7 to the troposphere. Relative depletion of the isotopes is generally observed after extensive precipitation that can also be attributed to wet maritime air mass effect, which can enhance Be washout from the atmosphere. The Be-10/Be-7 values obtained in this study range at 0.5-2.5 and show also a seasonal trend. Some of the high ratio values may also occur during the cold period months that likely reflect mixing of air masses with either different ages or origins. Intrusion of Be-10 depleted air masses from middle latitude may explain some of the variability in the isotopic ratio. Comparison of the isotopic ratios measured here with available data from the northern hemisphere and model cosmogenic production and distribution in the atmosphere suggests some overlap but also a wider range in the data measured here. Further variability in the isotopes distribution correlates with both short term (month to month) and long-term (about 10-11-year) changes in solar activity. An attempt is also performed here to compare the atmospheric Be-isotopes ranges measured in aerosols presented here with available Be-10 data of the ice cores in Greenland. This exercise is aimed to evaluate the reliability of magnitude changes in isotopic concentration in the ice with respect to effects of atmospheric production and regional climate factors.