Seasonal variation of atmospheric concentrations of 210Pb and 7Be at Tsukuba, Japan, with a possible observation of 210Pb originating from the 1991 eruption of Pinatubo volcano, Philippines

Abstract

Concentrations of 210Pb and 7Be in the surface air were measured at Tsukuba Science City (36°03) N, 140°07’ E), Japan, during the period of November 1987 to May 1992. The air concentrations of 210Pb and 7Be ranged from 0.2 to 0.8 mBq/m3and from 1 to 6 mBq/m3, respectively. Seasonal variation of 210Pb concentration was similar to that of 7Be, showing a “two-peak” variation pattern: high concentrations appeared in the spring and the fall. This variation pattern was formed on the 210Pb concentration generated from 222Rn in the surface air. This was interpreted as part of 222Rn emitted from the ground surface may be transported upwards to accumulate long-lived 210Pb in the lower part of the stratosphere. It may then subside into the troposphere with the cosmogenic 7Be through the tropopause break, during the spring, and along the descending currents, including those which accompany the migratory anticyclones passing frequently over Japan during the spring and fall. Unusual and temporal increase in the 210Pb concentration and in the 210Pb/7Be activity ratio observed in the winter months of 1991–1992 may be attributed partly to the 210Pb fallout originating from the 1991 eruption of Pinatubo volcano, Philippines. © 1994, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.