Spatio-Temporal Distribution of Atmospheric Radiocesium in Eastern Japan just after the TEPCO Fukushima Daiichi Nuclear Power Plant Accident—Analysis of Used Filter-Tapes of SPM Monitors in Air Quality Monitoring Stations—

Abstract

The spatio-temporal distributions of atmospheric ¹³⁷Cs concentrations in and around the Fukushima prefecture just after the Fukushima Daiichi Nuclear Power Plant (FD1NPP) accident were retrieved, by measuring radionuclides in suspended particulate matter (SPM) hourly collected on used filter-tapes of operational air quality monitoring stations. Analyzing a published dataset of radiocesium (¹³⁴Cs and ¹³⁷Cs) at around 100 SPM monitoring sites, 10 radioactive plumes/polluted air masses in which the maximum ¹³⁷Cs concentrations were higher than 10 Bq m^-3 were found in the period of March 12–23, 2011. In these plumes, 5 plumes were transported to the eastern and/or central parts of the Fukushima prefecture, and another 5 plumes were transported to the Kantou area located more than 100 km south of the FD1NPP, respectively. In the period, the maximum ¹³⁷Cs concentration of about 575 Bq m^-3 was observed in the east coast of the Fukushima prefecture on the evening of March 12, 2011, after a vent process and the hydrogen explosion of Unit 1. Furthermore, high ¹³⁷Cs concentrations of around 10 Bq m^-3 were found in the northern part of the FD1NPP on the morning of March 21 when a strong northerly wind began to blow. These results indicate that further study is expected on the relationship between the release of radionuclides and the events happened in the reactors of the FD1NPP, and on the effects of the vertical structure of the atmosphere on the surface concentrations of radionuclides.