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

摘要

Atmospheric fallout of naturally occurring cosmic radionuclide Be-7 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 Be-7 deposition to the surface. The monthly volume-weighted activities of Be-7 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 (alpha) indicates a higher depositional flux of Be-7 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 Be-7 was 590 Bq m(-2) y(-1), which is comparable with several Mediterranean coastal stations. The annual bulk depositional fluxes of Be-7 in the 30 degrees N - 50 degrees 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.

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