Cosmogenic ~7Be and ~(22)Na in ground level air in Switzerland (1994-2011)

摘要

We report monthly averages of weekly Be and Na concentrations in aerosol samples collected with high volume aerosol filters at 5 sampling sites in Switzerland from 1994 to 2011 (~7Be) and from 2000 to 2011 (~(22)Na). Monthly average concentrations of the two cosmogenic isotopes varied between 2600 and 4600 nBq/m~3 for ~7Be and between 0.2 μBq/m~3 and 0.5 μBq/m~3 for ~(22)Na. The ~(22)Na concentration in ground level air strongly increased from March to May, while a corresponding ~7Be increase was seen from March until July. The observed variations of the ~7Be and ~(22)Na activities together with the changes in the ~7Be/~(22)Na ratio indicate input of stratospheric air between March and May, increased mixing of upper tropospheric air from June to August, and less exchange between the upper and lower troposphere in autumn and winter. Additionally, the 11-year solar cycle is clearly seen in the annual averages of the ~7Be concentrations.