Spatial and temporal variations of atmospheric 85Kr observed during 1995-2001 in Japan:: Estimation of atmospheric 85Kr inventory in the northern hemisphere

Atmospheric Kr-85 concentrations have been continuously monitored since 1995 at the Meteorological Research Institute (MRI) in Tsukuba, Japan. They have also been observed once a year at several stations over the Japanese islands since 1995. The annual growth rate of the background atmospheric Kr-85 concentrations in Tsukuba was 0.03 Bq (.) m(-3 .) yr(-3) during 1996-2001. The atmospheric Kr-85 concentrations at several stations over Japan were within the range of the annual variations in Tsukuba. However, higher and lower Kr-85 concentrations in early winter, compared with those in Tsukuba (36.1 degreesN, 140.1 degreesE), occurred in Sapporo (43.1 degreesN, 141.3 degreesE) and Ishigaki (24.3 degreesN, 124.2 degreesE), respectively. The reason for this is that Sapporo is covered by a continental air mass, some from European sources, whereas Ishigaki is still covered by a subtropical air mass. The Northern Hemispheric background Kr-85 concentrations from 1994 to 2001 was calculated from the Kr-85 inventory and the release rate of Kr-85 from the nuclear fuel reprocessing plants in Europe. Calculated Kr-85 concentrations in surface air were in good agreement with annual average observed values at the MRI, Tsukuba. The global atmospheric inventory of Kr-85 in December 2001 was also estimated to be approximately 5 EBq by using observed data in Tsukuba.