Temporal variation and provenance of thorium deposition observed at Tsukuba, Japan

► We show monthly Th deposition observed at Tsukuba, Japan from 1990 to 2007. ► The Th deposition shows a seasonal variation and inter-annual variability. ► Th isotope ratios (230Th/232Th) are used to identify its sources. ► The long-term trend of Th deposition is related to increasing anthropogenic input.