Stratospheric Beryllium-7 intrusions into the troposphere at mid latitude 40 grad N with tropopause folding

A spring sampling and testing experiment by measuring 7Be concentrations in ground-level air was proposed and carried out 1996 at mid latitude 40 grad N in order to take the advantage of the statistically high probability of tropopause folding events occurring in the spring months at northern hemisphere. The results of the experiment showed a trend of increase of 7Be concentrations in air starting from the spring equinox (22 March) through July, resulting in a shift of the tropopause folding from spring to summer, not being narrow. At that period, Beryllium-7 concentrations in air reached up to 10.1 mBq m-3 (6 April 1996) and 9.9 mBq m-3 (6 June 1996), three times average environmental concentration of 7Be in the temperate zones (3 mBq m-3) in surface air as reported in UNSCEAR Report (1982). (Author) 2 figs., 17 refs