Short-term temporal variability of volatile contaminant concentrations in soil gas related to soil-atmosphere interface dynamics: Two case studies in the Veneto region (Italy).

The study of the variability of soil gas concentrations is crucial for defining effective monitoring and remediation strategies and for the risk assessment related to the emission of vapors from the subsurface. The traditional soil gas monitoring strategy consists of seasonal surveys based on short-time-averaged sampling. Soil gas monitoring results are often used to assess the risk associated with the emission of volatile contaminants from the subsurface, using models mainly based on molecular diffusion and therefore assuming continuous emission from the soil. At two contaminated sites located in the Veneto region (Italy), continuous monitoring using a photoionization detector, pressure gauges, and an ultrasonic anemometer was used to relate soil gas variability to surface and subsurface physical parameters. At both sites a cyclic diurnal variation of volatile organic compounds concentration in soil gas was observed, correlated with the variation of several meteorological parameters and in particular with the variation of the differential pressure between soil and atmosphere and the buoyancy vertical flux. These findings question the reliability of the conventional methodology employed in the collection and assessment of soil gas data. Integr Environ Assess Manag 2024;00:1-10. © 2024 SETAC.

Surprising concentrations of hydrogen and non-geological methane and carbon dioxide in the soil.

Due to its potential use as a carbon-free energy resource with minimal environmental and climate impacts, natural hydrogen (H2) produced by subsurface geochemical processes is today the target of intensive research. In H2 exploration practices, bacteria are thought to swiftly consume H2 and, therefore, small near-surface concentrations of H2, even orders of 102 ppmv in soils, are considered a signal of active migration of geological gas, potentially revealing underground resources. Here, we document an extraordinary case of a widespread occurrence of H2 (up to 1 vol%), together with elevated concentrations of CH4 and CO2 (up to 51 and 27 vol%, respectively), in aerated meadow soils along Italian Alps valleys. Based on current literature, this finding would be classified as a discovery of pervasive and massive geological H2 seepage. Nevertheless, an ensemble of gas geochemical and soil microbiological analyses, including bulk and clumped CH4 isotopes, radiocarbon of CH4 and CO2, and DNA and mcrA gene quantitative polymerase chain reaction analyses, revealed that H2 was only coupled to modern microbial gas. The H2-CO2-CH4-H2S association, wet soil proximity, and the absence of other geogenic gases in soils and springs suggest that H2 derives from near-surface fermentation, rather than geological degassing. H2 concentrations up to 1 vol% in soils are not conclusive evidence of deep gas seepage. This study provides a new reference for the potential of microbial H2, CH4 and CO2 in soils, to be considered in H2 exploration guidelines and soil carbon and greenhouse-gas cycle research.

Outdoor Radon Dose Rate in Canada's Arctic amid Climate Change.

Decades of radiation monitoring data were analyzed to estimate outdoor Radon Dose Rates (RnDRs) and evaluate climate change impacts in Canada's Arctic Regions (Resolute and Yellowknife). This study shows that the RnDR involves dynamic sources and complex environmental factors and processes. Its seasonality and long-term trends are significantly impacted by temperatures and soil-and-above water contents. From 2005 to 2022, Yellowknife's RnDR increased by +0.35 ± 0.06 nGy/h per decade, with the fastest increases occurring in cold months (October to March). The rise is largely attributable to water condition changes over time in these months, which also caused enhanced soil gas emissions and likely higher indoor radon concentrations. In Resolute, the RnDR increased between 2013 and 2022 at +0.62 ± 0.19 nGy/h (or 16% relatively) per decade in summer months, with a positive temperature relationship of +0.12 nGy/h per °C. This work also demonstrates the relevance of local climate and terrain features (e.g., typical active layer depth, precipitation amount/pattern, and ground vegetation cover) in researching climate change implications. Such research can also benefit from using supporting monitoring data, which prove effective and scientifically significant. From the perspective of external exposure to outdoor radon, the observed climate change effects pose a low health risk.

Impacts of LNAPL types on mechanisms and rate of natural source zone depletion.

Understanding the mechanisms of natural source zone depletion (NSZD) will support an improved understanding of the long-term sustainability of NSZD as a site remedy and how NSZD rates may change over time. This is the first study that has quantified and compared the rate of three NSZD mechanisms (methanogenesis, vaporization, and aqueous biodegradation) between two chemically distinct light non-aqueous phase liquid (LNAPL) source zones (aliphatic-rich naphtha for Zone #1 vs aromatic-rich pyrolysis gasoline for Zone #2) within the same geologic and climate conditions. The rates of NSZD attributable to vaporization (400 mg C/m2/d vs. 300 mg C/m2/d) and aqueous biodegradation (92 mg C/m2/d vs. 67 mg C/m2/d) were similar for Zone #1 and #2; however, the rate of methanogenesis NSZD was 6x higher in Zone #1 (1000 mg C/m2/d vs. 170 mg C/m2/d). These results suggest that the aliphatic hydrocarbons content in an LNAPL source may be a factor in the rate of methanogenesis NSZD. For both Zone #1 and #2, total NSZD rate determined using this "three mechanism" measurement method was in reasonable agreement with two other methods used to measure total NSZD rates (CO2 Gradient Method and Dynamic Closed Chamber Method), validating the "three mechanism" method as a tool to measure the total NSZD rate at a site and to provide an improved understanding of the predominant NSZD mechanism. Overall, this study highlights the importance of LNAPL type and chemical characteristics in determining source zone natural attenuation mechanism and its total rates.

Root and rhizosphere contribution to the net soil COS exchange.

Background and aims: Partitioning the measured net ecosystem carbon dioxide (CO2) exchange into gross primary productivity (GPP) and ecosystem respiration remains a challenge, which scientists try to tackle by using the properties of the trace gas carbonyl sulfide (COS). Its similar pathway into and within the leaf makes it a potential photosynthesis proxy. The application of COS as an effective proxy depends, among other things, on a robust inventory of potential COS sinks and sources within ecosystems. While the soil received some attention during the last couple of years, the role of plant roots is mostly unknown. In our study, we investigated the effects of live roots on the soil COS exchange. Methods: An experimental setup was devised to measure the soil and the belowground plant parts of young beech trees observed over the course of 9 months. Results: During the growing season, COS emissions were significantly lower when roots were present compared to chambers only containing soil, while prior to the growing season, with photosynthetically inactive trees, the presence of roots increased COS emissions. The difference in the COS flux between root-influenced and uninfluenced soil was fairly constant within each month, with diurnal variations in the COS flux driven primarily by soil temperature changes rather than the presence or absence of roots. Conclusion: While the mechanisms by which roots influence the COS exchange are largely unknown, their contribution to the overall ground surface COS exchange should not be neglected when quantifying the soil COS exchange. Supplementary Information: The online version contains supplementary material available at 10.1007/s11104-023-06438-0.

Soil processes modify the composition of volatile organic compounds (VOCs) from CO2- and CH4-dominated geogenic and landfill gases: A comprehensive study.

Degradation mechanisms affecting non-methane volatile organic compounds (VOCs) during gas uprising from different hypogenic sources to the surface were investigated through extensive sampling surveys in areas encompassing a high enthalpy hydrothermal system associated with active volcanism, a CH4-rich sedimentary basin and a municipal waste landfill. For a comprehensive framework, published data from medium-to-high enthalpy hydrothermal systems were also included. The investigated systems were characterised by peculiar VOC suites that reflected the conditions of the genetic environments in which temperature, contents of organic matter, and gas fugacity had a major role. Differences in VOC patterns between source (gas vents and landfill gas) and soil gases indicated VOC transformations in soil. Processes acting in soil preferentially degraded high-molecular weight alkanes with respect to the low-molecular weight ones. Alkenes and cyclics roughly behaved like alkanes. Thiophenes were degraded to a larger extent with respect to alkylated benzenes, which were more reactive than benzene. Furan appeared less degraded than its alkylated homologues. Dimethylsulfoxide was generally favoured with respect to dimethylsulfide. Limonene and camphene were relatively unstable under aerobic conditions, while α-pinene was recalcitrant. O-bearing organic compounds (i.e., aldehydes, esters, ketones, alcohols, organic acids and phenol) acted as intermediate products of the ongoing VOC degradations in soil. No evidence for the degradation of halogenated compounds and benzothiazole was observed. This study pointed out how soil degradation processes reduce hypogenic VOC emissions and the important role played by physicochemical and biological parameters on the effective VOC attenuation capacity of the soil.

Computed tomography scanning revealed macropore-controlled N2O emissions under long-term tillage and cover cropping practices.

Microscale alterations in soil physical characteristics resulting from long-term soil health practices can contribute to changes in soil nitrous oxide (N2O) emissions. In this study, we investigated soil N2O emissions in relation to pore characteristics influencing soil gas diffusivity under long-term tillage and cover cropping practices. Intact soil cores from tillage (conventional tillage, Conv. T versus no tillage, NT) and cover crop (hairy vetch, HV versus no cover crop, NC) treatments were used for N2O measurements and computed tomography (CT) scanning. Using X-ray CT technique with a resolution of 59 µm, pore structure parameters including macroporosity, number of macropores, anisotropy, fractal dimension, tortuosity, and connectivity were determined. The results showed that Conv. T and HV emitted significantly higher N2O than NT and NC, respectively. A similar trend was observed for macroporosity, Conv. T soils had 27.4 % higher CT-derived macroporosity than the NT soils and HV increased macroporosity by 31.1 % over the NC treatment. The number of macropores and fractal dimension were significantly higher whereas degree of anisotropy was significantly lower under HV compared to NC. In the upper 3 cm of soil, HV had a connected porosity, whereas the pores were disconnected and isolated in NC. These CT-derived properties; however, were not impacted by tillage treatments. N2O emissions were positively and significantly correlated to relative soil gas diffusivity, CT-derived macroporosity, number of macropores, and fractal dimension. Our results demonstrated that soil macroporosity and relative gas diffusivity could lead to improved understanding and predictability of N2O emissions under high soil moisture conditions.

Field demonstration for the solvent-based sampling method to perform compound-specific isotope analysis on gas-phase VOC.

The solvent-based sampling method for collecting gas-phase volatile organic compounds (VOCs) and conducting compound-specific isotope analysis (CSIA) was deployed during a controlled field study. The solvent-based method used methanol as a sink to accumulate petroleum hydrocarbons during the sampling of soil air and effluent gas. For each gaseous sample collected, carbon isotope analysis (δ13C) was conducted for a selection of five VOCs (benzene, toluene, o-xylene, cyclopentane and octane) emitted by a synthetic hydrocarbon source emplaced in the subsurface. The δ13C values obtained for gaseous VOCs (collected from soil gas and effluent gas) were compared to measurements obtained for the same VOCs present in the source material (none aqueous phase liquid - NAPL) and dissolved in groundwater to evaluate the reliability of the solvent-based sampling method in providing accurate isotope measurements. Since the NAPL source was composed of only 12 VOCs, potential bias related to the analytical procedure (such as co-elution) were avoided, hence emphasizing on field-related bias. This field evaluation demonstrated the capacity of the solvent-based method to produce precise and accurate δ13C measurements. The isotopic discrepancies between the gaseous and the NAPL values were < 1 ‰ for 39 out of the 41 comparison points, thus deemed not statistically different based on a common isotopic uncertainty error of ±0.5 ‰. Moreover, the current field study is the first field study to report δ13C measurements for up to five gas-phase VOCs obtained from the same sample, which appears to be of interest for VOC fate or forensic studies. The possibility to use several VOC isotopic measurements enabled by the sampling method would contribute to strengthen the connection assessment between gaseous VOCs and the suspected emitting source. Accordingly, the field results presented herein support the application of this sampling methodology to conduct CSIA assessment in the frame of VOC vapor studies.

Understanding petroleum vapor fate and transport through high resolution analysis of two distinct vapor plumes.

No field study has provided a detailed characterization of the molecular composition and spatial distribution of a vadose zone plume of petroleum volatile organic compounds (VOCs), which is critical to improve the current understanding of petroleum VOC transport and fate. This is study reports a high-resolution analysis of two distinct vapor plumes emanating from two different light non-aqueous phase liquid (LNAPL) sources (an aliphatic-rich LNAPL for Zone #1vs an aromatic-rich LNAPL for Zone #2) at a large petrochemical site. Although deep soil vapor signatures were similar to the source zone LNAPL signatures, the composition of the shallow soil vapors reflected preferential attenuation of certain hydrocarbons over others during upward transport in the vadose zone. Between deeper and shallower soil gas samples, attenuation of aromatics was observed under all conditions, but important differences were observed in attenuation to aliphatic compound classes. Attenuation of all aliphatic compounds was observed under aerobic conditions but little attenuation of any aliphatics was observed under anoxic conditions without methane. In contrast, under methanogenic conditions, paraffins attenuated more than isoparaffins and naphthenes. These results suggest that isoparafins and naphthenes may present more of a vapor intrusion risk than benzene or other aromatic hydrocarbons commonly considered to be petroleum vapor intrusion risk drivers. While the overall vapor composition changed significantly within the vadose zone, diagnostic ratios of relatively recalcitrant alkylcyclopentanes were preserved in shallow soil vapor samples. These alkylcyclopentanes may be useful for distinguishing between petroleum vapor intrusion and other sources of petroleum VOCs detected in indoor air.

Distribution of select per- and polyfluoroalkyl substances at a chemical manufacturing plant.

Per- and polyfluoroalkyl substances (PFAS) are used in various industrial products; however, they pose serious health risks. In this study, soil, soil gas, and groundwater samples were collected at a PFAS manufacturing facility in New Jersey, USA, to determine the presence and distribution of PFASs from the soil surface to groundwater and at various distances from the presumed source. Fluorotelomer alcohols (FTOHs) were detected in soil (< 0.26-36.15 ng/g) and soil gas (160-12,000 E µg/m3), while perfluorinated carboxylic acids (PFCAs) were found in soil (4.3-810 ng/g), soil gas (<0.10-180 µg/m3), and groundwater (37-49 µg/L). FTOH and PFCA concentrations decreased as the distance from the presumed source increased, suggesting that PFCAs are likely to migrate in groundwater, whereas FTOHs primarily move in the vapor phase. The presence of PFAS in the groundwater, soil, and soil gas samples indicate its potential for vapor intrusion; thus, some PFAS may contribute to indoor air inhalation exposure. To the best of our knowledge, this is the first report on the quantification of volatile PFAS in soil gas at a PFAS manufacturing facility.

Measurement of radon concentration in soil gas and radon exhalation rate from soil samples along and across the Main Central Thrust of Garhwal Himalaya, India.

The present study focuses on measuring radon concentrations in soil gas at various depths, radon exhalation rate (surface and mass) from soil samples, and gamma dose rate along and across the Main Central Thrust of Garhwal Himalaya, India. Radon concentration in soil gas, surface, and mass exhalation rates was measured using a portable SMART radon monitor (RnDuo). Furthermore, the gamma dose rate was measured using a pocket radiation monitor. The soil gas radon concentration varied from 15 ± 4 to 579 ± 82 Bq m-3 at a depth of 25 cm, 10 ± 2 to 533 ± 75 Bq m-3 at a depth of 30 cm, and 9 ± 1 to 680 ± 95 Bq m-3 at a depth of 35 cm. The surface and mass exhalation rates were found 3 ± 0.7 to 98 ± 3 Bq m-2 h-1 (with AM ± SD = 36 ± 28 Bq m-2 h-1) and 1 ± 0.2 to 95 ± 2 mBq kg-1 h-1 (with AM ± SD = 30 ± 22 mBq kg-1 h-1), respectively. The gamma dose rate for the present study area varies from 0.11 ± 0.05 to 0.28 ± 0.05 µSv h-1 with a mean value of 0.17 ± 0.05 µSv h-1. The correlation analysis between the exhalation rates (mass and surface) and radon concentration of soil gas at various depths was carried out in the current study.

Using groundwater monitoring wells for rapid application of soil gas radon deficit technique to evaluate residual LNAPL.

The application of the 222Radon (Rn) deficit technique using subsurface soil gas probes for the identification and quantification of light non-aqueous phase liquids (LNAPL) has provided positive outcomes in recent years. This study presents an alternative method for applying this technique in the headspace of groundwater monitoring wells. The developed protocol, designed for groundwater monitoring wells with a portion of their screen in the vadose zone, is based on the use of portable equipment that allows rapid measurement of the Rn soil gas activity in the vadose zone close to the water table (i.e., smear zone) where LNAPL is typically expected. The paper first describes the step-by-step procedure to be followed for the application of this method. Then, a preliminary assessment of the potential of the method was carried out at two Italian sites characterized by accidental gasoline and diesel spills into the subsurface from underground storage tanks. Although the number of tests conducted does not allow for definitive conclusions, the results obtained suggest that, from a qualitative point of view, Rn monitoring in the headspace of monitoring wells is a promising, fast, and minimally invasive screening method that could also potentially reduce the costs associated with field data acquisition. This method proves to be suitable for detecting the presence of LNAPL in both the mobile and residual phases with results consistent with the other lines of evidence available at the sites, such as groundwater and soil gas monitoring. Future efforts should be directed toward evaluating the accuracy of this method for a quantitative assessment of residual LNAPL saturations.

The Analysis of 222Rn and 220Rn Natural Radioactivity for Local Hazard Estimation: The Case Study of Cerveteri (Central Italy).

Radon (222Rn) is the second most common cause of lung cancer after smoking. As radon poses a significant risk to human health, radon-affected areas should be identified to ensure people's awareness of risk and remediation. The primary goal of this research was to investigate the local natural radioactivity (in soils, groundwater, and indoors) because of the presence of tuff outcrops (from middle-lower Pleistocene volcanic activity) that naturally produce radioactive gas radon at Cerveteri (Rome, Central Italy). The results of the radon survey highlighted moderate (>16,000 Bq/m3) but localized anomalies in soils in correspondence with a funerary site pertaining to the Etruscan Necropolis of Cerveteri, which extends over a volcanic rock plateau. Indoor radon measurements were performed at several tuff-made dwellings, and the results showed medium-low (<200 Bq/m3) values of indoor radon except for some cases exceeding the reference level (>300 Bq/m3) recommended by the 2013/59 Euratom Directive. Although no clinical data exist regarding the health effects of thoron (220Rn) on humans, the study of 220Rn average activity concentration in the soil gas survey reveals new insights for the interpretation of radon sources that can affect dwellings, even taking into account the considerable difference in the half-lives of 222Rn and 220Rn.

Application of airborne geophysical survey data in a logistic regression model to improve the predictive power of geogenic radon maps. A case study in Castleisland, County Kerry, Ireland.

In this study, a novel methodology was investigated to improve the spatial resolution and predictive power of geogenic radon maps. The data inputs comprise indoor radon measurements and seven geogenic factors including geological data (i.e. bedrock and Quaternary geology, aquifer type and soil permeability) and airborne geophysical parameters (i.e. magnetic field strength, gamma-ray radiation and electromagnetic resistivity). The methodology was tested in Castleisland southwest Ireland, a radon-prone area identified based on the results of previous indoor radon surveys. The developed model was capable of justifying almost 75 % of the variation in geogenic radon potential. It was found that the attributes with the greatest statistical significance were equivalent uranium content (EqU) and soil permeability. A new radon potential map was produced at a higher spatial resolution compared with the original map, which did not include geophysical parameter data. In the final step, the activity of radon in soil gas was measured at 87 sites, and the correlation between the observed soil gas radon and geophysical properties was evaluated. The results indicate that any model using only geophysical data cannot accurately predict soil radon activity and that geological information should be integrated to achieve a successful prediction model. Furthermore, we found that EqU is a better indicator for predicting indoor radon potential than the measured soil radon concentrations.

Geochemical precursory characteristics of soil gas Rn, Hg, H2, and CO2 related to the 2019 Xiahe Ms5.7 earthquake across the northern margin of West Qinling fault zone, Central China.

The Xiahe Ms5.7 earthquake occurred in Xiahe county, Gannan prefecture, China (35.10°N, 102.69°E) on October 28, 2019, with a source depth of 10 km. This study investigates the spatial and temporal evolution characteristics of cross-fault soil gas concentrations prior to the Xiahe Ms5.7 earthquake by analyzing Rn, Hg, H2, and CO2 data collected from 11 profiles across the northern margin of the West Qinling fault zone from 2016 to 2019. The spatial distribution of these gases showed varying trends, with Rn concentration intensity decreasing from the Wushan segment to the east and west sections, while Hg, H2, and CO2 all broke the trend in the West Qinling fault zone's northern margin. The soil gas concentration intensity demonstrated a significant response to the Xiahe Ms5.7 earthquake, particularly in the west Ganjia sections. By integrating the seismogenic model and numerical simulation results, we explored the physical mechanism underlying these abnormal trends. Our findings suggest that the continuous decline characteristic of fault gas could be a valuable indicator of fracture tectonic activity, while an upward trend after continuous decline may signal a medium and short-term seismogenic event in the source area. These results provide a foundation for improved tracking of earthquake location and timing in a fault zone through cross-fault soil gas methods, highlighting the importance of enhancing deep fluid flow monitoring and seismogenic model research in fault zones.

Influence of advection on the soil gas radon deficit technique for the quantification of LNAPL.

The Radon (Rn) deficit technique is a rapid, low-cost, and non-invasive method to identify and quantify light non-aqueous phase liquids (LNAPL) in the soil. LNAPL saturation is typically estimated from Rn deficit using Rn partition coefficients, assuming equilibrium conditions. This work examines the applicability of this method in the presence of local advective fluxes that can be generated by groundwater fluctuations or biodegradation processes in the source zone. To this end, a one-dimensional analytical model was developed to simulate the steady-state diffusive-advective transport of soil gas Rn in the presence of LNAPL. The analytical solution was first validated against an existing numerical model adapted to include advection. Then a series of simulations to study the effect of advection on Rn profiles were carried out. It was found that in high-permeability soils (such as sandy soils), advective phenomena can significantly affect Rn deficit curves in the subsurface compared with those expected, assuming either equilibrium conditions or a diffusion-dominated transport. Namely, in the presence of pressure gradients generated by groundwater fluctuations, applying the traditional Rn deficit technique (assuming equilibrium conditions) can lead to an underestimation of LNAPL saturation. Furthermore, in the presence of methanogenesis processes (e.g., in the case of a fresh LNAPL of petroleum hydrocarbons), local advective fluxes can be expected above the source zone. In such cases, Rn concentrations above the source zone can be higher than those above background areas without advective phenomena, resulting in Rn deficits higher than 1 (i.e., Rn excess), and thus leading to a wrong interpretation regarding the presence of LNAPL in the subsurface if advection is not considered. Overall, the results obtained suggest that advection should be considered in the presence of pressure gradients in the subsurface to ensure an effective application of the soil gas Rn-deficit technique for quantitative estimation of LNAPL saturation.

Antarctic permafrost degassing in Taylor Valley by extensive soil gas investigation.

Ongoing studies conducted in northern polar regions reveal that permafrost stability plays a key role in the modern carbon cycle as it potentially stores considerable quantities of greenhouse gases. Rapid and recent warming of the Arctic permafrost is resulting in significant greenhouse gas emissions, both from physical and microbial processes. The potential impact of greenhouse gas release from the Antarctic region has not, to date, been investigated. In Antarctica, the McMurdo Dry Valleys comprise 10 % of the ice-free soil surface areas in Antarctica and like the northern polar regions are also warming albeit at a slower rate. The work presented herein examines a comprehensive sample suite of soil gas (e.g., CO2, CH4 and He) concentrations and CO2 flux measurements conducted in Taylor Valley during austral summer 2019/2020. Analytical results reveal the presence of significant concentrations of CO2, CH4 and He (up to 3.44 vol%, 18,447 ppmv and 6.49 ppmv, respectively) at the base of the active layer. When compared with the few previously obtained measurements, we observe increased CO2 flux rates (estimated CO2 emissions in the study area of 21.6 km2 ≈ 15 tons day-1). We suggest that the gas source is connected with the deep brines migrating from inland (potentially from beneath the Antarctic Ice Sheet) towards the coast beneath the permafrost layer. These data provide a baseline for future investigations aimed at monitoring the changing rate of greenhouse gas emissions from Antarctic permafrost, and the potential origin of gases, as the southern polar region warms.

Development of a "222Rn incremented method" for the rapid determination of air exchange rate using soil gas.

The air exchange rate (AER) is a critical parameter that governs the levels of exposure to indoor pollutants impacting occupants' health. It has been recognized as a crucial metric in spreading COVID-19 disease through airborne routes in shared indoor spaces. Assessing the AER in various human habitations is essential to combat such detrimental exposures. In this context, the development of techniques for the rapid determination of the AER has assumed importance. AER is generally determined using CO2 concentration decay data or other trace gas injection methods. We have developed a new method, referred to as the "222Rn incremented method", in which 222Rn from naturally available soil gas was injected into the workplace for a short duration (∼30 min), homogenized and the profile of decrease of 222Rn concentration was monitored for about 2 h to evaluate AER. The method was validated against the established 222Rn time-series method. After ascertaining the suitability of the method, several experiments were performed to measure the AER under different indoor conditions. The AER values, thus determined, varied in a wide range of 0.36-4.8 h-1 depending upon the ventilation rate. The potential advantages of the technique developed in this study over conventional methods are discussed.

Environmental impacts of 222Rn, Hg and CO2 emissions from the fault zones in the western margin of the Ordos block, China.

Investigating the emissions of soil gas including radon, mercury and carbon dioxide (222Rn, Hg and CO2) from the solid earth to the atmosphere through active fault zones is of great significance for accession of atmospheric environment. In this study, the concentrations and fluxes of 222Rn, Hg and CO2 were measured at the main active fault zones at the western margin of the Ordos block, China. The concentrations of 222Rn, Hg and CO2 were in the range of 0-60.1 kBq m-3, 3-81 ng m-3 and 0.04-9.23%, respectively, while the fluxes of 222Rn, Hg and CO2 are in the range of 1.99-306.99 mBq m-2 s-1, 0-15.12 ng m-2 h-1 and 0-37.91 g m-2d-1, respectively. Most of the major fault zones at the study area are CO2 risk-free regions (CO2 concentration in soil gas < 5%). However, the extend of 222Rn pollution at the fault zones of F1, F4, F5 and F9 (the fault number) and that of Hg pollution at the fault zones of F2, F4, F5 and F7 were higher than the pollution level of 1. The annual emission of Hg and CO2 from the western margin of the Ordos block was estimated to be 2.03 kg and 0.70 Mt, respectively. Comprehensive analyses indicated that the higher emission rates of soil gases from the active fault zones were related to the seismic activities. The results suggest that the earthquake activity is a dominant factor enhancing the emission of 222Rn, Hg and CO2 from the solid earth through active fault zones and, furthermore, resulting great impact on the atmospheric environment.

Detailed Geogenic Radon Potential Mapping Using Geospatial Analysis of Multiple Geo-Variables-A Case Study from a High-Risk Area in SE Ireland.

A detailed investigation of geogenic radon potential (GRP) was carried out near Graiguenamanagh town (County Kilkenny, Ireland) by performing a spatial regression analysis on radon-related variables to evaluate the exposure of people to natural radiation (i.e., radon, thoron and gamma radiation). The study area includes an offshoot of the Caledonian Leinster Granite, which is locally intruded into Ordovician metasediments. To model radon release potential at different points, an ordinary least squared (OLS) regression model was developed in which soil gas radon (SGR) concentrations were considered as the response value. Proxy variables such as radionuclide concentrations obtained from airborne radiometric surveys, soil gas permeability, distance from major faults and a digital terrain model were used as the input predictors. ArcGIS and QGIS software together with XLSTAT statistical software were used to visualise, analyse and validate the data and models. The proposed GRP models were validated through diagnostic tests. Empirical Bayesian kriging (EBK) was used to produce the map of the spatial distribution of predicted GRP values and to estimate the prediction uncertainty. The methodology described here can be extended for larger areas and the models could be utilised to estimate the GRPs of other areas where radon-related proxy values are available.