Spatiotemporal variation of radon and carbon dioxide concentrations in an underground quarry: coupled processes of natural ventilation, barometric pumping and internal mixing

Reasons for large fluctuation of radon and CO<sub>2</sub> levels in a dead-end passage of a karst cave (Postojna Cave, Slovenia)

“…In general the ventilation of Postojna Cave is characterised by convective airflow, controlled mainly by the temperature difference between the cave and the outside atmosphere, as discussed by for one measurement location in the Velika Gora (Great Mountain) chamber of Postojna Cave. Different ventilation regimes in the cold and warm periods of the year are responsible for the observed seasonal pattern of radon concentration with low winter and high summer levels, as already reported for this Kobal et al, 1988;Vaupotič, 2008) and several other caves (Gillmore et al, 2002;Kowalczk and Froelich, 2010;Nagy et al, 2012;Perrier and Richon, 2010;Przylibski, 1999;Tanahara et al, 1997;Wilkening and Watkins, 1976).…”

“…Correlation between P out and P cave (pressure in the cave) was discussed byŠebela and Turk (2011) in the study of climate characteristics of Postojna Cave, where simultaneous pressure variations at the surface and at three locations in the underground was shown. Therefore, air pressure may in this case have an influence on radon concentration only by the effect of "barometric pumping" of radon from the pore space (Perrier and Richon, 2010). However, no significant influence of P out can be observed, possibly due to the obscured effect of pressure changes by airflows driven by temperature gradients.…”

“…All caves should be considered fragile systems, but show caves are particularly at risk because of anthropogenic impact. An understanding of cave microclimates is of great importance when studying the thermodynamics of karst processes, palaeoclimate proxies, hydrogeological aspects of speleothems, CO 2 build-up and cave ecosystems (Baldini et al, 2006;Faimon et al, 2011;Kowalczk and Froelich, 2010;Perrier and Richon, 2010;Spötl et al, 2005;Tremaine et al, 2011). The thermal and moisture characteristics of the cave air (Badino, 2010;De Freitas et al, 1982), as well as the concentration of gases ( 222 Rn, CO 2 ) and aerosols (Bezek et al, 2012) are mainly controlled by the degree of air exchange with the outside environment.…”

“…Variation of radon concentration in cave air arises from a balance of radon emission from cave surfaces and drip waters, its radioactive transformation, and exchange with the outside atmosphere (Wilkening and Watkins, 1976). Radon concentration in underground cave systems is also characterised by internal mixing of air masses (Perrier and Richon, 2010). In a study of 220 caves around the world, Hakl et al (1997) reported an annual average radon concentration of 2800 Bq m −3 .…”

Short-term <sup>222</sup>Rn activity concentration changes in underground spaces with limited air exchange with the atmosphere

“…The purpose of these analyses is to understand the mechanisms of these changes and identify their causes (i.e. Li et al, 2006;Perrier et al, 2007;Perrier and Richon, 2010). Having this in mind, the authors of this paper have also decided to investigate changes in radon activity concentration in underground tourist facilities in much smaller time ranges.…”