The temporal variation of stratospheric fallout derived from the Chernobyl accident

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公開日
1991-01
権利情報
  • https://www.elsevier.com/tdm/userlicense/1.0/
DOI
  • 10.1016/0265-931x(91)90053-i
公開者
Elsevier BV

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Abstract The monthly depositions of 90 Sr and caesium isotopes at Tsukuba through December 1988 are reported and the temporal variation of Chernobyl fallout is discussed. The measurements indicate that the radioactive fallout derived from the stratospheric Chernobyl radioactivity continued until the end of 1988. The annual 137 Cs deposits were 135, 0·95 and 0·57 Bq m −2 in 1986, 1987 and 1988, respectively. The annual 90 Sr deposits were 1·8 and 0·15 Bq m −2 in 1986 and 1987, respectively. In 1987, about 80% of the 137 Cs deposition and about 40% of the 90 Sr deposition were from Chernobyl radioactivity transported into the stratosphere. It is estimated that 5·1 × 10 −3 of the released caesium isotopes and 1·9 × 10 −3 of the released 90 Sr have been transported to the stratosphere. With regard to the altitude distribution of the stratospheric Chernobyl radioactivity, 46% was in the active mixing and exchange layer near the tropopause, while 54% was transported into the lower stratosphere. The 137 Cs/ 90 Sr activity ratio of the stratospheric Chernobyl radioactivity is estimated to be 12. The contribution of resuspension to annual deposition in 1987 was less than 1% for 134 Cs and 2% for 137 Cs. In 1988, it was less than 14% for 134 Cs and 34% for 137 Cs.

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