Variation analysis of atmospheric Be activity concentrations with respect to precipitation

降水による大気中Be濃度の変動解析

楢崎 幸範*; 迫田 晃弘   ; 赤田 尚史*; 伊藤 久徳*; 百島 則幸*

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

2011年4月から2015年12月の間、西日本の太宰府市において大気中及び降水中のBe濃度を毎日連続測定した。測定データを定量的に解析し、降水によるBe濃度の変動を明らかにした。非降水日の平均濃度は5.5mBq/m、降水日は3.8mBq/mであった。この平均的な濃度差31%(1.7mBq/m)はウォッシュアウト効果によるもので、夏季に顕著であった。Be濃度と降水量の関係について、降水量が5.0mm/dayと少ない場合には同程度の濃度で推移し、5.0-10.0mm/dayの降水量では減少傾向を示した(ただし有意ではない)。降水量が10mm/dayの場合、Be濃度は有意に減少した。また、2日続けて降水があった場合、2日目のBe濃度は降水量によらず有意に減少した。

Beryllium-7 activity concentrations in the atmosphere and precipitation were continuously measured every day between April 2011 and December 2015 in Dazaifu, western Japan. The measured data were quantitatively analyzed to determine the precipitation-induced variation in Be activity concentrations. The average concentrations on nonprecipitation and precipitation days were 5.5 and 3.8 mBq/m, respectively. This difference of 31% (1.7 mBq/m) on average, was attributable to the washout effect, which was more significant in the summer. Regarding the association between Be activity concentration and precipitation, the concentration remained at a similar level for the small precipitation amount of 5.0 mm/day and showed a decreasing trend (but was insignificant) for the precipitation of 5.0-10.0 mm/day. A significant decrease in the concentration was observed for 10 mm/day. Furthermore, when precipitation occurred on two successive days, the Be activity concentrations on the second day significantly decreased regardless of precipitation.