Fluctuations of CO₂ and 222Rn concentration in the karst vadose zone: Comparing exhalation, indoor concentrations, and cave air dynamics (Nerja Cave, Southern Spain)

IF 8.2 1区环境科学与生态学 Q1 ENVIRONMENTAL SCIENCES

Science of the Total Environment Pub Date : 2025-05-23 DOI:10.1016/j.scitotenv.2025.179723

C. Liñán , I. Vadillo , J. Benavente , S. Cañete , L. Ojeda

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引用次数: 0

Abstract

To investigate the influence of atmospheric and subsurface karst conditions on gas transport in the vadose zone and across the epikarst-atmosphere interface, we measured: a) radon (²²²Rn) and carbon dioxide (CO₂) concentrations in the air of two boreholes drilled in the vadose zone, where high levels of these gases had been previously reported, and b) indoor radon concentrations in two dwellings built on potentially karstifiable lithologies. One dwelling (D1) is located near the boreholes and a major tourist cave (Nerja Cave), while the other (D2) is in the town of Nerja.

Periodic fluctuations in gas concentrations were observed in the boreholes, reflecting advective transport of atmospheric air into the subsurface (inflow) and from the vadose zone into the atmosphere (outflow). Gas transport was mainly driven by barometric pumping, whose efficiency depends on vadose zone permeability, although thermal-induced convection was also detected. Advective transport was more effective in winter than in summer. In the dwellings, high ²²²Rn concentrations resulted from subsurface radon infiltration into the buildings. Radon transport indoors was mainly driven by depressurization of the dwellings due to temperature gradients and barometric pumping (D1), as well as wind effects and ventilation habits (D2).

The presence of large karstic cavities may play a supplemental role in the indoor radon concentrations in nearby buildings. Finally, some anomalies in vadose air radon concentrations appear to be linked to seismic activity, though further research is needed to confirm this relationship.

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岩溶气包带CO₂和222Rn浓度波动：比较呼出、室内浓度和洞穴空气动力学（西班牙南部Nerja洞穴）

为了研究大气和地下喀斯特条件对气包带和跨表岩溶-大气界面的气体输送的影响，我们测量了：a)在气包带钻探的两个钻孔的空气中氡（222Rn）和二氧化碳（CO2）的浓度，这些气体的含量很高，之前曾有报道，b)在潜在可岩溶岩性上建造的两个住宅的室内氡浓度。其中一个住所（D1）位于钻孔和一个主要的旅游洞穴（Nerja洞穴）附近，而另一个住所（D2）位于Nerja镇。在钻孔中观测到气体浓度的周期性波动，反映了大气空气向地下（流入）和从水汽带向大气（流出）的平流输送。气体输运主要由气压泵送驱动，其效率取决于气相带渗透率，但也存在热致对流。平流运输在冬季比夏季更有效。在住宅中，222Rn浓度高是由于地下氡渗入建筑物造成的。氡在室内的迁移主要是由温度梯度和气压泵（D1）以及风的影响和通风习惯（D2）引起的住宅降压驱动的。大型岩溶洞的存在可能对附近建筑物的室内氡浓度起补充作用。最后，气态空气中氡浓度的一些异常似乎与地震活动有关，尽管需要进一步的研究来证实这种关系。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Science of the Total Environment 环境科学-环境科学

CiteScore

17.60

自引率

10.20%

发文量

8726

审稿时长

2.4 months

期刊介绍： The Science of the Total Environment is an international journal dedicated to scientific research on the environment and its interaction with humanity. It covers a wide range of disciplines and seeks to publish innovative, hypothesis-driven, and impactful research that explores the entire environment, including the atmosphere, lithosphere, hydrosphere, biosphere, and anthroposphere. The journal's updated Aims & Scope emphasizes the importance of interdisciplinary environmental research with broad impact. Priority is given to studies that advance fundamental understanding and explore the interconnectedness of multiple environmental spheres. Field studies are preferred, while laboratory experiments must demonstrate significant methodological advancements or mechanistic insights with direct relevance to the environment.