Measurement of the 36Cl deposition flux in central Japan: natural background levels and seasonal variability

► We monitored 36Cl in precipitation in central Japan over a period of >5 years. ► The 36Cl flux varied seasonally, with a peak in spring. ► The long-term average 36Cl flux and the initial 36Cl/Cl ratio were 32 ± 2 atoms m−2 s−1 and (41 ± 6) × 10−15, respectively. ► An observation period covering an 11-year solar cycle would yield more accurate estimates of the values, given the increased 36Cl flux during the solar minimum.