Variations of Be-7 concentrations in surface air at Nagano City

Abstract

The concentrations of Be-7 in surface air at Nagano City (36 deg 39 min N, 138 deg 12 min E) have been measured during the period from August 2000 to December 2003. The average monthly concentrations of Be-7 in surface air were in the range of 3.3 to 14 mBq/cu m with pronounced two peaks, showing clearly maxima in spring and autumn and minima in winter and summer. This tendency, two-peak variation pattern, found at Nagano City is almost in agreement with those observed at Osaka, Chiba, and Tsukuba in Japan. When comparing the present data at Nagano City with those at these cities, the most remarkable difference is that in winter the values at Nagano City are apparently lower, which may be conjectured that this difference is mainly due to snowfall, that is, at Nagano City there is a lot of snowfall during winter, on the other hand, at Osaka, Chiba, and Tsukuba very little. Anticorrelation between events of precipitation and concentrations of Be-7 was observed, and it is considered that wet precipitation is one of the main and important factors for the variations of Be-7 concentrations in air, especially as a short-period reduction. A pronounced increase in the concentrations of Be-7 was sometimes found in winter that is expected for the Be-7 concentrations to be in a low level which was interpreted as a low pressure trough coming close to the Japanese Islands with high concentrations of Be-7 is responsible for a marked increase in surface air concentrations of Be-7 under the characteristic distribution of atmospheric pressure around the Japanese Islands.