Observation of the Movement of the Precipitation by Using Tritium Tracer

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Tracer techniques have proven to be one of the most powerful tools to characterize the movement of air mass and pollutant transport in hydrological systems. In order to clarify the behavior of low-level tritium in the rain water, we have employed the measuring method of tritium applying a distillation process and an electrolytic enrichment process. The activity of tritium (T specific activity) in the obtained water was measured by liquid scintillation counter. This procedure was applied to bulk precipitation, imitative ground infiltrated precipitation and short term precipitation collected in Niigata City. Moreover, we investigated the concentrations of cations (Na+, K+, Ca2+, and Mg2+) in the precipitation to associate with air mass transport patterns arriving at the place. From the above mentioned, next matters have been clarified:(1) T specific activity in precipitation was found to have a strong dependence on location and season. (2) The chemical components in precipitation during typhoon have notable character of marine air mass. (3) Associated ions in monthly precipitation showed seasonal variation, in fact, the seasonal variation of Ca2+ and tritium were very similar. (4) Backward trajectory analysis method is useful for the analysis of the behavior of T specific activity and several ions in short-term precipitation.
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