Measurement and analysis of long-term variation of atmospheric Be activity concentrations in Dazaifu (western Japan)

Narazaki, Yukinori*; Sakoda, Akihiro   ; Akata, Naofumi*; Ito, Hisanori*; Momoshima, Noriyuki*

Atmospheric Be activity concentration was continuously measured in Dazaifu, western Japan, from 1999 to 2020, and its variation was analyzed. Daily Be data analysis, encompassing an analysis for 22 years, revealed a concentration range of not detected - 18 mBq/m, characterized by substantial monthly variation and smoothed annual variation. An average daily Be activity concentration of 5.0 2.6 mBq/m was considered to be representative at the ground-surface-level in 30-40N. Results from a two-way Analysis of variance (ANOVA) indicated statistical significance in monthly and annual Be variabilities. The monthly variability of Be activity concentration was approximately four times greater than the annual variability. Frequency analysis revealed that the monthly variability comprised major 12-month and minor 6-month periodicities. The substantial decrease in Be activity concentration during summer, a primary driver of monthly variation, was also observed at other locations in Japan, attributed to a stable high-pressure system in the Pacific Ocean that stalled over Japan's southern seas, followed by the inflow of air masses containing low Be activity concentrations. The annual variation was primarily influenced by the 11-year solar activity cycle, which affects the intensity of cosmic rays that produce Be.