Cs-137 detection at CTBT radionuclide monitoring stations in East Asia

Abstract

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) Okinawa radionuclide monitoring station (JPP37) is located on a hill facing the East China Sea at the center of the main island of Okinawa. It occasionally detects Cs-137, although no nuclear facilities are located on the island. This study focused on the detection of Cs-137 at JPP37 and examined the ratio of simultaneous detections at neighboring stations and the relationship with Asian dust from inland East Asia. The detection of Cs-137 from 2020 to 2023 at JPP37, which was the target of the analysis, was higher in the spring. Among the nine CTBT radionuclide stations in East Asia, the detections in Beijing, Lanzhou, and Ulaanbaatar, Mongolia, were also high in spring. This suggested a high association with the detection of Asian dust in East Asia. Thus, we confirmed the detection of Cs-137 at nine nearby international monitoring system (IMS) of Comprehensive Nuclear-Test-Ban Treaty Preparatory Organization (CTBTO) stations when Asian dust was observed at any of the sites in Japan. In addition, we observed that the detection rates were high in Takasaki, Beijing, Lanzhou, and Ulaanbaatar. It can be inferred that the Cs-137 observed mainly in spring at the IMS particle radionuclide station in the East Asian region around Japan was likely to pick up the effects of global fallout conveyed by Asian dust. Thereafter, we conducted a preliminary source estimation analysis for Asian dust arrival near Japan. Atmospheric dispersion simulations explained the detection of Cs-137 at nearby IMS particle radionuclide stations, assuming that Cs-137 was emitted from the desert, the source of the Asian dust.