Factors controlling the air ventilation of a limestone cave revealed by ^(222)Rn and ^(220)Rn tracers

다국어 초록 (Multilingual Abstract)

We monitored ^(222)Rn (half life: 3.82 d) and ^(220)Rn (half life: 56 s) activities every hour in a limestone cave, Seongryu Cave, Korea, from May to July 2010. The activities of both nuclides in this cave were highest at night and lowest during the day owing to active ventilation with outside air during the day. As the outside air temperature increased from May to July, ^(222)Rn activity increased by 2–3 times. A simple mixing model of hourly ^(222)Rn variation revealed that the ventilation with outside air decreased by a factor of 3–4 from May to July. The daily average of ^(222)Rn activities correlated well with the daily average temperature of the outside air, indicating that the ventilation with outside air is controlled mainly by outside-air density, rather than by the diurnal amplitude of the outside air temperature. Although the trend of the diurnal variation of ^(220)Rn was similar to that of ^(222)Rn, its increase from May to July was only 65%. Since the short-lived ^(220)Rn does not have any stacking effect over different days and the diffusive flux is negligible, ^(220)Rn activities indicated increases in the advective pore-air input rates of cave rocks from May to July, which are consistent with the modeling result of hourly ^(222)Rn variations. Thus, our study suggests that the dual Rn tracers provide key information on the micro- and macro air-ventilation processes of caves.

참고문헌 (Reference)

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