Temporal variation of monthly 137Cs deposition observed in Japan: Effects of the Fukushima Daiichi nuclear power plant accident

• We describe depositional behaviors of radionuclides derived from the Fukushima Daiichi NPP.
• Monthly 137Cs deposition decreased from March 2011 to October 2011 and exhibited small peak in spring 2012.
• Monthly 137Cs deposition decreased with increasing distance from the Fukushima Daiichi NPP.
• Resuspension is one of the possible processes supported the higher monthly 137Cs deposition in 2012.

Monthly 137Cs depositions from March 2011 to April 2012 were reported at monitoring stations within about 250 km from the Fukushima Daiichi NPP. The monthly 137Cs deposition at each station decreased with apparent half-lives of 11–14 d during the period from March to June 2011, and after July 2011 its decrease rates changed. Second peaks of the monthly 137Cs deposition occurred in February–April 2012, which may be supported by resuspension of 137Cs bearing particles.