Measurements of atmospheric 7Be properties using high-efficiency gamma spectroscopy.

Two 7Be-related properties have been measured using a high-efficiency germanium gamma spectrometer (relative efficiency of 90%), namely, the activity median aerodynamic diameter (AMAD) of 7Be-associated atmospheric aerosols and the airborne 7Be radioactivity. With time resolutions of about 1-3d correlations between these 7Be-related properties and different meteorological parameters were identified. We found that AMAD is anti-correlated to 7Be counts. It is correlated with the relative humidity (RH) and mean cloud cover with high confidence, but not with temperature. We also found that 7Be radioactivity was correlated with the RH with a moderate confidence, but not with the mean cloud cover or temperature. Furthermore, wet precipitation present in the middle of the sampling period decreased the 7Be activity and increased the AMAD, while wet precipitation before or at the beginning of the sampling period decreased both 7Be activity and AMAD. Finally, after a cold front passed by, the AMAD decreased and the 7Be activity increased. Possible explanations are also given.