Distribution Of 222Rn Research Articles

Distribution of 222Rn and CO2 across faults and its origin in Wayang Windu geothermal area, West Java - Indonesia

As a geogenic gas, 222Rn (radon) has been widely utilized to infer permeability zones in some geological settings such as fault zones, volcanic and geothermal areas. In this study, soil 222Rn was measured in Wayang Windu geothermal area to infer the relation between fault and permeability. In addition, measurement of soil CO2 and its δ13C composition were also performed to infer transport mechanism and the origin of soil CO2. The high and anomaly soil 222Rn, i.e., above 8,500 Bq/m3, were found in the south - southwest area and related to Pejaten Fault, Banjarsari Fault and Cibitung Fault. In contrast, low soil 222Rn was found in the northern area, where several highly productive geothermal wells are located. The high and anomaly soil CO2 concentrations were also found in a relatively similar area with high 222Rn, but not closely related to the fault structures. Furthermore, the δ13C composition showed that the origin of soil CO2 in the area was magmatic, biogenic and atmospheric. Based on the 222Rn/CO2 values and its δ13C compositions, the mechanism of 222Rn transport was interpreted as independent from CO2 as carrier gas.

Distribution of 222Rn in Seawater Intrusion Area and Its Implications on Tracing Submarine Groundwater Discharge on the Upper Gulf of Thailand

Abstract Radon (222Rn) has been widely employed as a tracer for estimating submarine groundwater discharge (SGD). However, the uncertainty of the SGD estimation remains significant, due to the spatial variability of radon in groundwater. In this study, we analyzed the hydrochemical proprieties of seawater and coastal groundwater in the Upper Gulf of Thailand and discussed the distribution characteristics of 222Rn in aquifers in terms of aquifer lithology, groundwater system recharge conditions, and water retention time. The results suggested that the residence time of groundwater and the process of groundwater salinization have the greatest impact on the distribution of 222Rn activity. A 222Rn mass balance model, synthesizing the distribution characteristics of 222Rn in groundwater and tidal influences on SGD, was built to estimate the submarine groundwater discharge in the Upper Gulf of Thailand. The result showed that the SGD flux of the Upper Gulf of Thailand was 0.0203 m/d. Moreover, there is a positive correlation between tidal height and the activity of 222Rn in groundwater. The SGD observed during the low tide was about 1.25 times higher than that observed during the high tide. This may influence the marine geochemical cycles of elements and their impact on marine ecosystems.

Radon traced seasonal variations of water mixing and accompanying nutrient and carbon transport in the Yellow-Bohai Sea

Radon (222Rn) is a natural radioactive tracer widely utilized to evaluate water exchange and mixing processes; however, minimal studies have investigated the 222Rn distribution in the Yellow-Bohai Sea (YBS) and its behavior is poorly understood. In this study, the seasonal distribution of 222Rn in the YBS was investigated. The results found that the 222Rn distribution in surface waters is significantly affected by rivers, while 222Rn activity in bottom waters is highly affected by submarine groundwater discharge. The eddy diffusivity and advection velocities of the YBS were obtained utilizing an improved 1D steady-state 222Rn diffusion-advection model. The average horizontal eddy diffusivities in the wet (August 2015) and dry (November 2014) seasons were 4.54 × 108 and 2.28 × 108 cm2 s−1 in dry season, respectively and the average vertical eddy diffusivity was 4.99 cm2 s−1. The dissolved inorganic nutrient (N, P, and Si) and dissolved inorganic carbon flux outputs from vertical eddy diffusion were determined to be 4.85, 0.29, 3.59, and 61.6 mmol m−2 d−1, respectively. These results demonstrate that eddy diffusion tracing in coastal ocean is conducive to interpreting water mixing processes and can be utilized to understand offshore nutrient and carbon transport better.

Natural 222Rn as a tracer of mixing and volatilization in a shallow aquifer during a CO2 injection experiment

AbstractThis study aims to evaluate the application of 222Rn in groundwater as a tracer for monitoring CO2 plume migration in a shallow groundwater system, which is important to detect potential CO2 leakage in the carbon capture and storage (CCS) project. For this research, an artificial CO2‐infused water injection experiment was performed in a shallow aquifer by monitoring hydrogeochemical parameters, including 222Rn. Radon in groundwater can be a useful tracer because of its sensitivity to sudden changes in subsurface environment. To monitor the CO2 plume migration, the data were analysed based on (a) the influence of mixing processes on the distribution of 222Rn induced by the artificial injection experiment and (b) the influence of a carrier gas role by CO2 on the variation of 222Rn. The spatio‐temporal distributions of radon concentrations were successfully explained in association with horizontal and vertical mixing processes by the CO2‐infused water injection. Additionally, the mixing ratios of each monitoring well were calculated, quantitatively confirming the influence of these mixing processes on the distribution of radon concentrations. Moreover, one monitoring well showed a high positive relationship between 222Rn and Total dissolved inorganic carbon (TIC) by the carrier gas effect of CO2 through volatilization from the CO2 plume. It indicated the applicability of 222Rn as a sensitive tracer to directly monitor CO2 leakage. When with a little effect of carrier gas, natural 222Rn in groundwater can be used to compute mixing ratio of CO2‐infused water indicative of CO2 migration pathways. CO2 carrier gas effect can possibly increase 222Rn concentration in groundwater and, if fully verified with more field tests, will pose a great potential to be used as a natural tracer for CO2.

Distribution of 222RN on the Continental Shelf in Southern Brazil and its Relation with Groundwater Discharge

Distribution of 222RN on the Continental Shelf in Southern Brazil and its Relation with Groundwater Discharge

Correlations of 226Ra and 222Rn activity concentrations in surface soil and groundwater of basement complex geological area of southwest Nigeria

The quantitative evaluations of naturally occurring radioisotopes in environmental media have provided significant information on the geological and radiological characteristics of different environments around the world. In furtherance to a preliminary study within southwest Nigeria set out to determine the distribution of 222Rn in groundwater and soil gas, the present study employed a well-shielded NaI(Tl) and RAD 7 detectors to determine activity concentrations of 226Ra and 222Rn in the media. Samples were collected from 100 sampling sites spatially distributed within the study area. Multivariate statistics were employed to extract the relationships between the activity concentrations of 226Ra and 222Rn in order to ascertain their origin and behavior in the basement complex geological area of southwest Nigeria. The mean activity concentration of 226Ra falls below the world average value of 35 Bq kg−1 in soil as reported by UNSCEAR, and 222Rn mean activity concentration is lower than 100 Bq l−1 recommended by WHO and European Commission as the criterion level in utility water for the members of the public. It can therefore be concluded that there is no significant radiological risks to the environment and human health due the presence of the measured radionuclides in soil and groundwater.

Evaluation of 222Rn and 220Rn discriminating concentration measurements with pinhole-based twin cup dosimeters using computational fluid dynamics simulations

Pinhole-based twin cup dosimeters are capable of distinguishing 222Rn and 220Rn passively, as well as measuring their concentrations via Solid State Nuclear Track Detector films. However, the reliability of the measurements can be affected by environmental conditions and design of the device. To evaluate the significance of diffusion coefficient of air, radius, length, and number of pinholes, as well as radius and length of the twin cups on the effectiveness of the device, computational fluid dynamics models were developed for 14 scenarios. Concentration distributions of 222Rn and 220Rn were obtained, with their transmission factors each calculated and compared for the twin cups and for the pinhole(s). The results suggest that little to no impact was made on 222Rn's transmission factors, despite the change in diffusion coefficient and dimensions of the pin hole and the twin cup. However, for 220Rn, transmission factors significantly increased with an increase in pinhole radius, number of holes, or diffusion coefficient, or a decrease in pinhole length, twin cup length, or twin cup radius.

ATTILA 4.0: Lagrangian advective and convective transport of passive tracers within the ECHAM5/MESSy (2.53.0) chemistry–climate model

Abstract. We have extended ATTILA (Atmospheric Tracer Transport in a LAgrangian model), a Lagrangian tracer transport scheme, which is online coupled to the global ECHAM/MESSy Atmospheric Chemistry (EMAC) model, with a combination of newly developed and modified physical routines and new diagnostic and infrastructure submodels. The new physical routines comprise a parameterisation for Lagrangian convection, a formulation of diabatic vertical velocity, and the new grid-point submodel LGTMIX to calculate the mixing of compounds in Lagrangian representation. The new infrastructure routines simplify the transformation between grid-point (GP) and Lagrangian (LG) space in a parallel computing environment. The new submodel LGVFLUX is a useful diagnostic tool to calculate online vertical mass fluxes through horizontal surfaces. The submodel DRADON was extended to account for emissions and changes of 222Rn on Lagrangian parcels. To evaluate the new physical routines, two simulations in free-running mode with prescribed sea surface temperatures were performed with EMAC–ATTILA in T42L47MA resolution from 1950 to 2010. The results show an improvement of the tracer transport into and within the stratosphere when the diabatic vertical velocity is used for vertical advection in ATTILA instead of the standard kinematic vertical velocity. In particular, the age-of-air distribution is more in accordance with observations. The global tropospheric distribution of 222Rn, however, is simulated in agreement with available observations and with the results from EMAC in grid space for both Lagrangian systems. Additional sensitivity studies reveal an effect of inter-parcel mixing on the age of air in the tropopause region and the stratosphere, but there is no significant effect for the troposphere.

Unperturbed, high spatial resolution measurement of Radon-222 in soil-gas depth profile

This work presents a method for measuring the depth distribution of 222Rn activity in soil gas. The method is based on the capacity of polycarbonates to absorb 222Rn and on the possibility of performing sensitive measurements of 222Rn absorbed by the polycarbonates via liquid scintillation counting (LSC). The method is the following: cylindrical holes are drilled along a metal rod and Makrofol® N polycarbonate foils enclosed in polyethylene envelopes are placed in each hole. The rod is driven into the soil and kept for a certain time. As long as the rod is in the soil, the polycarbonate foils are exposed to the 222Rn concentration at their depth. At the end of the exposure the rod is pulled out and the foils are transferred to liquid scintillation (LS) vials filled with liquid scintillator. The 222Rn absorbed in the foils is then measured with a LS analyzer. The rod with the polycarbonate foils acts as a passive probe which senses the 222Rn concentration at different depths beneath the ground surface. The achievable minimum detectable 222Rn activity concentration with the equipment and conditions used in this study is around 12.5 kBq/m3. It can easily be lowered below 1 kBq/m3 if larger foils and low-background LS analyzers are used. Since the method does not require air sampling the depth distribution of 222Rn in the soil is unperturbed by the sampling. The spatial distribution and the maximum measurement depth are set by the distance between the holes and the depth to which the rod can be fixed into the ground. Results from in situ applications of the method in terrains with high 222Rn in soil-gas are reported, which demonstrate the feasibility and the usefulness of the proposed approach.

Distribution of 222Rn in groundwater and estimation of resulting radiation dose to different age groups: A case study from Bangalore City

ABSTRACTIngesting waters holding high levels of natural occurring radioactive element like Radon would contribute to increase in the effective dose received by people followed by an increased prevalence of cancer. The current study is an attempt to describe the extent of contribution of 222Rn to natural background radiation and the resultant effective dose to public of different age groups. In order to do so, 65 groundwater samples from selected parts of Bangalore city were collected and analyzed for radon activity using RAD7 radon monitor coupled with RAD H2O accessories. The radon activity was in the range of 3.05–696 Bq/L (mean: 91.39 Bq/L) and 92.31% of the groundwater samples recorded elevated radon concentration above the United States environmental protection agency (USEPA's) Maximum Contaminant Level (MCL) value of 300 pCi/L, corresponding to 11.1 Bq/L. The mean annual effective dose contribution of people falling under different age groups (viz., infants, children, teens: males and females, adults: males and females, pregnant and lactating women) due to ingestion of water-borne 222Rn ranged from 0.082 to 0.444 mSv/y and was found to be higher in all the age groups of males compared to respective female age groups, but well within the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and World Health Organization (WHO) proposed limit of 1 mSv/y.

Time dependence of [formula omitted]Rn, [formula omitted]Rn and their progenies’ distributions in a diffusion chamber

Diffusion chamber with SSNTD (Solid State Nuclear Track Detector) placed inside is a passive detector for measuring the activity of 222Rn and 220Rn (radon and thoron) and their progenies. Calibration from detected alpha particle tracks to progeny activity is often acquired from theoretical models. One common assumption related to these models found in literature is that concentrations of 222Rn and 220Rn at the entrance of a chamber are constant during the exposure. In this paper, concentrations of 222Rn and 220Rn at the entrance of the chamber are taken to be variable with time, which is actually the case in reality. Therefore, spatial distributions of 222Rn and 220Rn and their progenies inside the diffusion chamber should be time dependent. Variation of 222Rn and 220Rn concentrations on the entrance of the chamber was modeled on the basis of true measurements. Diffusion equations in cylindrical coordinates were solved using FDM (Finite Difference Method) to obtain spatial distributions as functions of time. It was shown that concentrations of 222Rn, 220Rn and their progenies were not homogeneously distributed in the chamber. Due to variable 222Rn and 220Rn concentrations at the entrance of the chamber, steady state (the case when concentration of 222Rn, 220Rn and their progenies inside the chamber remains unchanged with time) could not be reached. Deposition of progenies on the chamber walls was considered and it was shown that distributions of deposited progenies were not uniform over walls’ surface.

The high-resolution version of TM5-MP for optimized satellite retrievals: description and validation

Abstract. We provide a comprehensive description of the high-resolution version of the TM5-MP global chemistry transport model, which is to be employed for deriving highly resolved vertical profiles of nitrogen dioxide (NO2), formaldehyde (CH2O), and sulfur dioxide (SO2) for use in satellite retrievals from platforms such as the Ozone Monitoring Instrument (OMI) and the Sentinel-5 Precursor, and the TROPOspheric Monitoring Instrument (tropOMI). Comparing simulations conducted at horizontal resolutions of 3° × 2° and 1° × 1° reveals differences of ±20 % exist in the global seasonal distribution of 222Rn, being larger near specific coastal locations and tropical oceans. For tropospheric ozone (O3), analysis of the chemical budget terms shows that the impact on globally integrated photolysis rates is rather low, in spite of the higher spatial variability of meteorological data fields from ERA-Interim at 1° × 1°. Surface concentrations of O3 in high-NOx regions decrease between 5 and 10 % at 1° × 1° due to a reduction in NOx recycling terms and an increase in the associated titration term of O3 by NO. At 1° × 1°, the net global stratosphere–troposphere exchange of O3 decreases by ∼ 7 %, with an associated shift in the hemispheric gradient. By comparing NO, NO2, HNO3 and peroxy-acetyl-nitrate (PAN) profiles against measurement composites, we show that TM5-MP captures the vertical distribution of NOx and long-lived NOx reservoirs at background locations, again with modest changes at 1° × 1°. Comparing monthly mean distributions in lightning NOx and applying ERA-Interim convective mass fluxes, we show that the vertical re-distribution of lightning NOx changes with enhanced release of NOx in the upper troposphere. We show that surface mixing ratios in both NO and NO2 are generally underestimated in both low- and high-NOx scenarios. For Europe, a negative bias exists for [NO] at the surface across the whole domain, with lower biases at 1° × 1° at only ∼ 20 % of sites. For NO2, biases are more variable, with lower (higher) biases at 1° × 1° occurring at ∼ 35 % ( ∼ 20 %) of sites, with the remainder showing little change. For CH2O, the impact of higher resolution on the chemical budget terms is rather modest, with changes of less than 5 %. The simulated vertical distribution of CH2O agrees reasonably well with measurements in pristine locations, although column-integrated values are generally underestimated relative to satellite measurements in polluted regions. For SO2, the performance at 1° × 1° is principally governed by the quality of the emission inventory, with limited improvements in the site-specific biases, with most showing no significant improvement. For the vertical column, improvements near strong source regions occur which reduce the biases in the integrated column. For remote regions missing biogenic source terms are inferred.

Variación espacial de la composición de 222Rn en los acuíferos Barva y Colima Superior, Costa Rica

MEN: El 222Rn es un trazador natural que permite determinar la conectividad entre las aguas subterráneas y las superficiales. El estudio presenta el primer análisis espacial de 222Rn en aguas subterráneas, superficiales y agua potable de la red de abastecimiento en los acuíferos Barva y Colima Superior en el Valle Central de Costa Rica. Se analizó la composición de 222Rn, δ18O y otras variables físico-químicas in situ en un total de 40 sitios de muestreo. En general, las nacientes de la zona norte presentaron una composición homogénea de 222Rn con una concentración promedio de 21,3 Bq/L. La concentración de 222Rn en los pozos varió entre 2,0 Bq/L y 50,5 Bq/L. Las altas concentraciones de 222Rn en algunos pozos pueden atribuirse a la desgasificación profunda a través de los fallamientos locales. En la red de abastecimiento de agua potable, la concentración de 222Rn varió entre 4,7 Bq/L y 30,8 Bq/L. Los valores encontrados en la red de abastecimiento, superiores al límite sugerido por la Agencia de Protección Ambiental de los Estados Unidos (11,1 Bq/L) para agua de consumo humano, pueden atribuirse al corto tiempo de residencia del agua de extracción subterránea en la red de abastecimiento. La utilización de tanques de almacenamiento o captación permitiría aumentar el tiempo de residencia del agua antes de ingresar a la red de consumo, facilitando la pérdida de 222Rn hacia la atmósfera o por decaimiento radioactivo. Asimismo, un análisis espacial es requerido a escala nacional, especialmente, en áreas de fallas activas o actividad volcánica.

The Role of Ocean Tides on Groundwater-Surface Water Exchange in a Mangrove-Dominated Estuary: Shark River Slough, Florida Coastal Everglades, USA

Low-relief environments like the Florida Coastal Everglades (FCE) have complicated hydrologic systems where surface water and groundwater processes are intimately linked yet hard to separate. Fluid exchange within these low-hydraulic-gradient systems can occur across broad spatial and temporal scales, with variable contributions to material transport and transformation. Identifying and assessing the scales at which these processes operate is essential for accurate evaluations of how these systems contribute to global biogeochemical cycles. The distribution of 222Rn and 223,224,226Ra have complex spatial patterns along the Shark River Slough estuary (SRSE), Everglades, FL. High-resolution time-series measurements of 222Rn activity, salinity, and water level were used to quantify processes affecting radon fluxes out of the mangrove forest over a tidal cycle. Based on field data, tidal pumping through an extensive network of crab burrows in the lower FCE provides the best explanation for the high radon and fluid fluxes. Burrows are irrigated during rising tides when radon and other dissolved constituents are released from the mangrove soil. Flushing efficiency of the burrows—defined as the tidal volume divided by the volume of burrows—estimated for the creek drainage area vary seasonally from 25 (wet season) to 100 % (dry season) in this study. The tidal pumping of the mangrove forest soil acts as a significant vector for exchange between the forest and the estuary. Processes that enhance exchange of O2 and other materials across the sediment-water interface could have a profound impact on the environmental response to larger scale processes such as sea level rise and climate change. Compounding the material budgets of the SRSE are additional inputs from groundwater from the Biscayne Aquifer, which were identified using radium isotopes. Quantification of the deep groundwater component is not obtainable, but isotopic data suggest a more prevalent signal in the dry season. These findings highlight the important role that both tidal- and seasonal-scale forcings play on groundwater movement in low-gradient hydrologic systems.

Off-line algorithm for calculation of vertical tracer transport in the troposphere due to deep convection

Abstract. A modified cumulus convection parametrisation scheme is presented. This scheme computes the mass of air transported upward in a cumulus cell using conservation of moisture and a detailed distribution of convective precipitation provided by a reanalysis dataset. The representation of vertical transport within the scheme includes entrainment and detrainment processes in convective updrafts and downdrafts. Output from the proposed parametrisation scheme is employed in the National Institute for Environmental Studies (NIES) global chemical transport model driven by JRA-25/JCDAS reanalysis. The simulated convective precipitation rate and mass fluxes are compared with observations and reanalysis data. A simulation of the short-lived tracer 222Rn is used to further evaluate the performance of the cumulus convection scheme. Simulated distributions of 222Rn are evaluated against observations at the surface and in the free troposphere, and compared with output from models that participated in the TransCom-CH4 Transport Model Intercomparison. From this comparison, we demonstrate that the proposed convective scheme in general is consistent with observed and modeled results.

Radionuclides analysis in hot spring waters in Korea by liquid scintillation counting

Tritium and 14C concentration in hot spring water in Korea were determined. Tritium in the most hot spring samples could not detected and concentration range was <0.5–1.31 TU. And 14C contents were ranged 1.7–78.6 pMC. From the 3H and 14C analysis, we found some hot springs are mixed with recent groundwater and hot spring water ages were estimated from 1,940 to 32,800 years. And also, 226Ra and 228Ra were determined simultaneously in hot spring water, and some other radionuclides were also analyzed. Content distribution of 222Rn was 50–3,760 pCi/L, 226Ra was <0.003–0.15 Bq/L and 228Ra was below the detection limit.

Measurement of Rn-222 in water by absorption in polycarbonates and liquid scintillation counting

This work presents a new technique for measurement of activity concentrations of Rn-222 in water which is based on liquid scintillation counting (LSC) of polycarbonates exposed in the water. The polycarbonate material has high absorption ability to radon and when exposed in a radon-containing environment (air or water), it absorbs and concentrates radon in its volume. This property of the polycarbonate material is used for sampling 222Rn from the water. The main new element in this work is that it proposes the LSC technique for measurement of the radiation, emitted from the polycarbonate material. This radiation is due to the decay of the absorbed 222Rn and its progeny. Experimental results of LSC of polycarbonate granules and thin foils exposed in water with different activity concentrations of Rn-222 are presented. In all cases a very good linear correlation between the LS counting rate and the activity concentration of the water is found. The LSC of polycarbonates shows similar or even higher sensitivity in comparison to that of LSC of water. The estimated radon-in-water minimal detectable activity concentrations of the proposed method are similar or lower than those of the LSC and lower than those obtained by gamma spectrometry. The proposed method is simple, robust, inexpensive and avoids the need of taking water samples for laboratory analysis. It facilitates studies of the spatial distribution of 222Rn in water basins by exposure of polycarbonate specimens at different spots or depths and subsequent liquid scintillation counting.

Po-210 and Pb-210 as atmospheric tracers and global atmospheric Pb-210 fallout: a Review

Over the past ∼5 decades, the distribution of 222Rn and its progenies (mainly 210Pb, 210Bi and 210Po) have provided a wealth of information as tracers to quantify several atmospheric processes that include: i) source tracking and transport time scales of air masses; ii) the stability and vertical movement of air masses iii) removal rate constants and residence times of aerosols; iv) chemical behavior of analog species; and v) washout ratios and deposition velocities of aerosols. Most of these applications require that the sources and sink terms of these nuclides are well characterized. Utility of 210Pb, 210Bi and 210Po as atmospheric tracers requires that data on the 222Rn emanation rates is well documented. Due to low concentrations of 226Ra in surface waters, the 222Rn emanation rates from the continent is about two orders of magnitude higher than that of the ocean. This has led to distinctly higher 210Pb concentrations in continental air masses compared to oceanic air masses. The highly varying concentrations of 210Pb in air as well the depositional fluxes have yielded insight on the sources and transit times of aerosols. In an ideal enclosed air mass (closed system with respect to these nuclides), the residence times of aerosols obtained from the activity ratios of 210Pb/ 222Rn, 210Bi/ 210Pb, and 210Po/ 210Pb are expected to agree with each other, but a large number of studies have indicated discordance between the residence times obtained from these three pairs. Recent results from the distribution of these nuclides in size-fractionated aerosols appear to yield consistent residence time in smaller-size aerosols, possibly suggesting that larger size aerosols are derived from resuspended dust. The residence times calculated from the 210Pb/ 222Rn, 210Bi/ 210Pb, and 210Po/ 210Pb activity ratios published from 1970’s are compared to those data obtained in size-fractionated aerosols in this decade and possible reasons for the discordance is discussed with some key recommendations for future studies. The existing global atmospheric inventory data of 210Pb is re-evaluated and a ‘ global curve’ for the depositional fluxes of 210Pb is established. A current global budget for atmospheric 210Po and 210Pb is also established. The relative importance of dry fallout of 210Po and 210Pb at different latitudes is evaluated. The global values for the deposition velocities of aerosols using 210Po and 210Pb are synthesized.

Temporal variation of 222Rn at the summit of Mt. Fuji associated with the Asian continental outflow

Concentrations of 222Rn were observed at the summit of Mt. Fuji (35.4°N, 138.7°E; 3776 m above sea level) in Japan from October 2002 to September 2003. These observations were analyzed using a global three-dimensional model. Daily 222Rn concentrations varied from 0.2 to 2.5 Bq m −3. The variation exhibited a slight seasonal cycle with high values in winter and summer. Day-to-day variation of 222Rn concentrations in winter had a large amplitude, depending on differences in transport processes from the Asian continent. In winter, higher concentrations of 222Rn were observed in an air mass with ascending motion advected from the middle latitudes of the eastern Asian continent where the 222Rn concentration of the air mass was high. In contrast, a lower concentration was observed in the air mass in winter, with a descending motion advected from Siberia where the 222Rn amount was low. The high amplitude of temporal variation of 222Rn in summer was due to the alternation of air masses originated from the continent or the ocean. The relatively low amplitude of day-to-day variation during spring and autumn was a reflection of the vertically uniform distribution of 222Rn in the air column over the Asian continent, where uniformity was produced by vertical mixing due to turbulence and thermal convection. The seasonal variation was linked to the East Asian monsoon circulation, with the westerly jet shifted northward or southward depending on the season. The main export of 222Rn was around 25 to 55°N during the winter and into the spring, shifting northward to around 30–70°N during the summer.

Characterization of the &amp;lt;sup&amp;gt;222&amp;lt;/sup&amp;gt;Rn family turbulent transport in the convective atmospheric boundary layer

Abstract. The combined effect of turbulent transport and radioactive decay on the distribution of 222Rn and its progeny in convective atmospheric boundary layers (CBL) is investigated. Large eddy simulation is used to simulate their dispersion in steady state CBL and in unsteady conditions represented by the growth of a CBL within a pre-existing reservoir layer. The exact decomposition of the concentration and flux budget equations under steady state conditions allowed us to determine which processes are responsible for the vertical distribution of 222Rn and its progeny. Their mean concentrations are directly correlated with their half-life, e.g. 222Rn and 210Pb are the most abundant whereas 218Po show the lowest concentrations. 222Rn flux decreases linearly with height and its flux budget is similar to the one of inert emitted scalar, i.e., a balance between on the one hand the gradient and the buoyancy production terms, and on the other hand the pressure and dissipation at smaller scales which tends to destroy the fluxes. While 222Rn exhibits the typical bottom-up behavior, the maximum flux location of the daughters is moving upwards while their rank in the 222Rn progeny is increasing leading to a typical top-down behavior for 210Pb. We also found that the relevant radioactive decaying contributions of 222Rn short-lived daughters (218Po and 214Pb) act as flux sources leading to deviations from the linear flux shape. In addition, while analyzing the vertical distribution of the radioactive decay contributions to the concentrations, e.g. the decaying zone, we found a variation in height of 222Rn daughters' radioactive transformations. Under unsteady conditions, the same behaviors reported under steady state conditions are found: deviation of the fluxes from the linear shape for 218Po, enhanced discrepancy in height of the radioactive transformation contributions for all the daughters. In addition, 222Rn and its progeny concentrations decrease due to the rapid growth of the CBL. The analysis emphasizes the crucial role of turbulent transport in the behavior of 222Rn n morning concentrations, in particular the ventilation at the top of the boundary layer that leads to the dilution of 222Rn by mixing with radon low concentration air.