Study of seasonal variation of accident-derived atmospheric radiocesium in Koriyama City, Fukushima Prefecture, Japan during 2011–2014.

This article focuses on the measurement and analysis of atmospheric radiocesium concentrations and deposition flux in Koriyama City, Fukushima Prefecture, Japan, from November 2011 to October 2014 following the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. The study found clear seasonal variations in radiocesium levels, with higher concentrations during winter to early spring and lower levels in summer to autumn, a pattern differing from that observed in more forested areas like Namie Town. The research suggests that atmospheric radiocesium concentrations are influenced by resuspension from contaminated ground surfaces and wind direction, particularly winds carrying particles from areas with higher deposition west of Koriyama City. Additionally, the study reports that the resuspension factor, which quantifies the release of radiocesium from surfaces back into the atmosphere, decreased over time with an effective half-life of approximately 0.94 years, reflecting land use differences between urbanized Koriyama and forested Namie Town.