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220 Rn/ 222 Rn Isotope Pair as a Natural Proxy for Soil Gas Transport

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Huxol Stephan, Brennwald Matthias S., Henneberger Ruth, Kipfer Rolf,
Project Rn-220 (Thoron) in ground water and soil gas (Continuation)
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Original article (peer-reviewed)

Journal Environmental Science & Technology
Volume (Issue) 47(24)
Page(s) 14044 - 14050
Title of proceedings Environmental Science & Technology
DOI 10.1021/es4026529

Open Access

URL https://pubs.acs.org/doi/abs/10.1021/es4026529
Type of Open Access Repository (Green Open Access)

Abstract

Radon (Rn) is a naturally occurring radioactive noble gas, which is ubiquitous in soil gas. Especially, its long-lived isotope 222Rn (half-life: 3.82 d) gained widespread acceptance as a tracer for gas transport in soils, while the short-lived 220Rn (half-life: 55.6 s) found less interest in environmental studies. However, in some cases, the application of 222Rn as a tracer in soil gas is complex as its concentrations can be influenced by changes of the transport conditions or of the 222Rn production of the soil material. Due to the different half-lives of 220Rn and 222Rn, the distances that can be traveled by the respective isotopes before decay differ significantly, with 220Rn migrating over much shorter distances than 222Rn. Therefore, the soil gas concentrations of 220Rn and 222Rn are influenced by processes on different length scales. In laboratory experiments in a sandbox, we studied the different transport behaviors of 220Rn and 222Rn resulting from changing the boundary conditions for diffusive transport and from inducing advective gas movements. From the results gained in the laboratory experiments, we propose the combined analysis of 220Rn and 222Rn to determine gas transport processes in soils. In a field study on soil gases in the cover soil of a capped landfill we applied the combined analysis of 220Rn and 222Rn in soil gas for the first time and showed the feasibility of this approach to characterize soil gas transport processes.
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