Atmospheric fallout of 7Be in bulk precipitation at the Adriatic coast, Croatia

Abstract

ABSTRACT Atmospheric fallout of naturally occurring cosmic radionuclide 7Be was monitored in bulk precipitation over a year (July 2018 to June 2019) at a coastal station (Martinska) of the Adriatic Sea, Croatia. The monthly depositional fluxes varied between 25.08 and 78.97 Bq m−2 month−1 (average: 49.18 ± 19.17 Bq m−2 month−1) and showed a significant correlation with precipitation (r = 0.92). The highest seasonal flux observed in winter (172 ± 4.31 Bq m−2 season−1) coincides with the highest amount of precipitation (190 mm), suggesting an important role of precipitation in the scavenging process of 7Be deposition to the surface. The monthly volume-weighted activities of 7Be varied from 0.63 to 5.74 Bq L−1 (average: 1.96 ± 1.7 Bq L−1) with the highest value corresponding to the summer season. The precipitation-normalised enrichment factor (α) indicates a higher depositional flux of 7Be in the summer season than the desired value due to the stratosphere-troposphere exchange and the contribution of dry deposition. The annual bulk depositional flux of 7Be was 590 Bq m−2 y−1, which is comparable with several Mediterranean coastal stations. The annual bulk depositional fluxes of 7Be in the 30°N - 50°N latitude band showed a good correlation with precipitation and established that the atmospheric fallout of this radionuclide is mainly governed by precipitation in that given latitude band.