The German Federal Office for Radiation Protection (Bundesamt für Strahlenschutz, BfS) is legally obliged to continuously monitor radioactivity in the environment in Germany. The Atmospheric Radioactivity and Trace Analysis Section of the BfS is operating four different measurement facilities/laboratories in Southern Germany: gamma spectrometry, radiochemistry and noble gas laboratories in Freiburg i.Br. and the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) monitoring station RN33 on Mt. Schauinsland. The three laboratories provide data of radioactive aerosol bound particulates such as Cs, U, Pu or Sr and noble gases (Kr and Xe) for the German Integrated Measurement and Information System (IMIS). The radionuclide station RN33 is monitoring radioactive particulates and Xe for the International Monitoring System (IMS) of the CTBTO. The variation of radioactivity on aerosol bound particles over time and the analysis of their origin, distribution and transport in the environment will be presented.

To collect aerosol bound particles, ground-level air sampling is carried out by high volume air samplers located in Freiburg i.Br. and on Mt. Schauinsland. The high volume air sampler is operated with two filter layers: an upper polypropylene layer with a collection efficiency of about 85% to 95% and a bottom fibre glass layer with a collection efficiency of almost 100%. The fibre glass filter is used as a control for collection efficiency of the polypropylene filter. As required by the German IMIS monitoring programmes, the routine sampling period is seven days, which can be reduced to daily cycles in case of (un)expected enhanced activity concentrations. The filters are separately pressed to pellets and analysed by high resolution γ-spectrometry. In addition, the polypropylene-filters are processed radioanalytically and analysed with a low level α/β-counting system and α-spectrometry.

The applied methods together with atmospheric transport modelling allow to detect smallest amounts of radioactive substances as well as to investigate their origin, distribution and transport in the environment. In addition, the Cs-137/Sr-90 ratios can be used as a geochemical fingerprint for source identification. Current (2022) median activity concentrations in ground-level air for Cs-137 and Sr-90 (2021) are 0.42 µBq m^-³ and 0.06 µBq m^-³, respectively. Detection limit (LOD) for Cs-137 is on average 0.14 µBq m^-³ in weekly samples and 0.01 µBq m^-³ in monthly samples for Sr-90. In March 2022 dust blown in from the Sahara towards Southern Germany resulted in slightly higher airborne Cs-137 activity concentrations while Sr-90 did not markedly change. Other sources for increased Cs-137 activity concentrations include past above ground nuclear weapons tests or resuspension of fallout from the Chernobyl accident. Thus, trace analysis is used to track short- and long-term changes in radioactivity in the environment at lowest activity levels.

How to cite: Baur, S., Schmid, S., Bieringer, J., and Bollhöfer, A.: On the trail of Cs-137 and Sr-90 – Trace analysis to monitor radioactivity in air, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15860, https://doi.org/10.5194/egusphere-egu23-15860, 2023.

The Catalan Environmental Radiological Surveillance Network consists of different types of scintillation gamma spectrometry detectors for the continuous and real-time automatic measurement of environmental radiation. The Network has a total of 35 monitors that obtain spectra every 10 minutes: 23 direct measurement monitors (13 with LaBr₃(Ce), 5 SrI₂(Eu) and 5 NaI (Tl) detectors), 10 particulate filter monitors (9 with LaBr₃(Ce) detectors and 1 with SrI₂(Eu)) and 2 river water monitors.

A method for the automatic and real-time quantification of the activity concentration of artificial, natural and NORM isotopes was developed and tested in the laboratory. The uncertainties in the activity concentrations, as well as the corresponding detection limits, were calculated applying the ISO-11929 standard. The developed and validated method that is exposed in the present study will be implemented shortly in all the stations of the Network.

The method is based on the analysis by spectral regions or ROIs (Regions of Interest). The method eliminates from the ROIs of the artificial (or NORM) isotopes of study the contributions due to emissions of natural isotopes (overlapping and Compton radiation), the ambient background, the possible intrinsic background of the detector and the contributions of other possible isotopes. As a result, an equation is generated for each isotope that allows us to obtain its net activity concentration (Bq/m3). This procedure is applied to determine the activity concentration of isotopes of natural origin (²¹²Pb, ²¹⁴Pb and ²¹⁴Bi), artificial (¹³¹I, ¹³⁷Cs and ⁶⁰Co) and NORM (²³⁴Th).

The method successfully eliminates the contribution of natural elements, intrinsic background and Compton contribution, both in situations with high and low activity of natural isotopes. Therefore, it allows obtaining the net activity concentration of the artificial isotopes of interest and eliminates the presence of false positives that could be produced by the presence of natural isotopes.

How to cite: Cerezo, A., Prieto, E., Reichardt, I., Casanovas, R., and Salvadó, M.: A fast algorithm for real-time monitoring of artificial radioisotopes in presence of variable natural radioactivity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7900, https://doi.org/10.5194/egusphere-egu23-7900, 2023.

The unique physical and chemical characteristics of radon make it an excellent tracer of atmospheric mixing and transport processes. As such, it has long been a species of interest to the climate change research communities. However, reliable, high resolution radon flux maps are essential for the use of atmospheric radon in climate studies.

Validation of the existing radon flux maps and inventories is currently limited by the availability of systematic measurements of radon fluxes and other process-relevant parameters (e.g., physical characteristics and moisture content of soil). Localised measurements of radon flux, soil moisture and soil physical properties can provide some information to validate and improve flux maps.  On the other hand, high sensitivity atmospheric radon measurements in conjunction with atmospheric transport models would determine the relative representativeness of radon flux models over larger scales.

To tackle the validation of radon flux maps, atmospheric radon measurements were compared to the results of modelled radon concentrations calculated using the Lagrangian particle model, the Met Office Numerical Atmospheric Modelling Environment (NAME) and two available versions of European radon flux maps¹. For this purpose, radon data from three UK greenhouse gases atmospheric monitoring stations located in Heathfield (an inland, 100 m tall tower), Tacolneston (an inland, 185 m tall tower), and Weybourne (a coastal site, 10 m tower) were used. The differences between measured and modelled radon concentrations on diurnal and monthly scales will be presented and discussed. The ratio of measured-modelled radon concentrations shows the potential to objectively assess the reliability of radon flux maps under different wind directions and atmospheric mixing conditions.

¹ 2015: doi:10.1594/PANGAEA.854715 and 2022: ICOS data search (icos-cp.eu).

How to cite: Kikaj, D., Chung, E., Saba, M., Karstens, U., Manning, A., Rennick, C., Ganesan, A., Foster, G., O’Doherty, S., Wenger, A., and Arnold, T.: Atmospheric radon measurements to assess the relative representativeness of radon flux models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12074, https://doi.org/10.5194/egusphere-egu23-12074, 2023.

The vertical mixing state of the atmosphere, as well as the atmospheric boundary layer (ABL) height, are important atmospheric transport model parameters for the accurate simulation of greenhouse gas concentrations. In order to use tall tower greenhouse gas measurements to quantify regional scale emissions (top-down, inverse estimates) an estimate of the atmospheric transport model uncertainty across the time series of study is needed. Several methods have been used to estimate this, often relying on arbitrary thresholds or a combination of parameters (such as vertical gradients if a gas is measured at multiple points). Here we study if radon has potential as an independent measurement to assess model uncertainty.

Radon is a radioactive noble gas present in our atmosphere and is a good tracer of mixing processes in the ABL due to its properties. Hence, measurements of atmospheric radon concentration can provide useful insights into the vertical mixing state of the atmosphere, and in turn may help to calibrate and validate atmospheric dispersion models.

In this study, we use high temporal resolution atmospheric measurements of radon and CH₄ from four tall tower sites in the UK, which are part of the Deriving Emissions linked to Climate Change (DECC) network: Heathfield (HFD), Ridge Hill (RGH), Tacolneston (TAC) and Weybourne (WAO). At each site, CH₄ is measured at two or three different heights, while radon is measured at one height.

To determine a metric whereby single-height measurements of radon can provide a proxy for vertical mixing states, we compare the diurnal cycle of the measured radon concentration with the modelled radon (calculated by the Met Office Numerical Atmospheric Modelling Environment (NAME) dispersion model and radon flux maps). The largest uncertainties are shown to be before sunrise and after sunset right before the inversion layer was formed/destroyed. The diurnal CH₄ vertical gradient at these times is also compared with the modelled CH₄ vertical gradient.

How to cite: Saba, M., Kikaj, D., Chung, E., Manning, A., Karstens, U., Rennick, C., Ganesan, A., Forster, G., O'Doherty, S., Wenger, A., and Arnold, T.: Can radon measurements at tall towers provide information on atmospheric vertical mixing states?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12151, https://doi.org/10.5194/egusphere-egu23-12151, 2023.

Atmospheric transport models used for nuclear emergency purposes are dedicated to simulating the atmospheric transport of radionuclides released from a damaged nuclear facility. The quality of this response is crucial and must be constantly improved. However, long-range measurement campaigns for validation are scarce, especially for radioactive pollutants. An effective way to do so is by simulating the radon-222 which is a non-reacting atmospheric tracer species with quite well-known exhalation rate and well-known nuclear transitions.

Radon-222 is naturally emitted. Its flux spatial variation is mainly due to the type of soil and rocks, rather than the vegetation or land use. Temporal variations are mainly led by soil humidity, leading to a monthly variation. The monthly surface radon flux map of Karstens and Levin, 2022 is used in this study.

The availability of the observations at suitable temporal and spatial scales is achieved in this study thanks to the Integrated Carbon Observation System, ICOS (Heiskanen et al. 2021). ICOS provides standardized and open data from more than 39 atmosphere stations that measures greenhouse gases concentrations in the atmosphere. Some stations also provide radon-222 concentrations measurements. Among them, some also include measurements at different heights - from ground level up to 200 meters – which is valuable to validate the vertical atmospheric transport modelling. The limited set of radon-222 stations is not a substitute for performing the comprehensive validation against a large variety of observations but gives valuable information on the performance of air concentration predictions. A previous study using the dose rate measurements network (Quérel et al. 2022), required in addition the need of an accurate deposition modelling to assess gamma dose rates at ground level due to wet deposition of radon-222 decay products.

We evaluate here the overall performance of an air concentration modelling chain: Karstens radon-222 fluxes, Météo-France ARPEGE numerical weather predictions and IRSN LdX operational atmospheric transport model. Simulated radon-222 air concentrations are compared with observations from the ICOS monitoring network over Europe, on an hourly frequency basis over one year. On initial examination, the model appears to under-predict radon-222 concentrations and some possible explanations and sources of improvement are identified.

References:

Heiskanen, J., C. Brümmer, N. Buchmann, C. Calfapietra, H. Chen, B. Gielen, T. Gkritzalis, S. Hammer, S. Hartman, M. Herbst, et al. (2021), The Integrated Carbon Observation System in Europe, Bulletin of the American Meteorological Society, 1 - 54, doi:10.1175/bams-d-19-0364.1.

Karstens, U. and Levin, I. (2022). traceRadon monthly radon flux map for Europe 2006-2022 (based on GLDAS-Noah v2.1 soil moisture), https://hdl.handle.net/11676/ge5vMeklvG_Qz43rzcS2wx0-

Quérel, A., Meddouni, K., Quélo, D., Doursout, T., and Chuzel, S. (2022). Statistical approach to assess radon-222 long-range atmospheric transport modelling and its associated gamma dose rate peaks. Advances in Geosciences. 57. 109-124. 10.5194/adgeo-57-109-2022.

How to cite: Quérel, A., Hached, T., Quélo, D., Ramonet, M., Yver Kwok, C., and Karstens, U.: Atmospheric transport modelling of radon-222 at European scale: description and validation against ICOS observations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14656, https://doi.org/10.5194/egusphere-egu23-14656, 2023.

The objective of the present study is to simulate the spectral gamma-ray response of the Swiss Airborne Gamma-Ray Spectrometry system (SAGRS) using Monte Carlo radiation transport codes. The SAGRS is mounted in the cargo bay of a AS-332M1 Super Puma helicopter from the Swiss Air Force and consists of four prismatic NaI(Tl) scintillation crystals with a total volume of 16.8 l. We developed a high-fidelity Monte Carlo model of the SAGRS including the detector system and the helicopter using the multi-purpose radiation transport code FLUKA. As part of the measurement campaign ARM22c organized by the National Emergency Operations Centre (NEOC), we performed hover and line flights in combination with ground measurements using certified ¹³³Ba and ¹³⁷Cs point sources to validate our model. The performed measurements revealed a significant impact of the helicopter fuel on the detector response for various solid angles. In general, we found an excellent agreement between the measured and simulated detector response with relative errors in the full energy peak <10%. The validated model presented herein offers a novel way to simulate the spectral detector response of the SAGRS for the generation of fundamental spectra in a full spectrum analysis framework.

How to cite: Breitenmoser, D., Butterweck, G., Kasprzak, M. M., and Mayer, S.: Validation of a High-Fidelity Monte Carlo Model for Airborne Gamma-Ray Spectrometry with Field Measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6130, https://doi.org/10.5194/egusphere-egu23-6130, 2023.

This study describes the equipment implementation of a mobile gamma spectrometry unit using LaBr₃ detectors and the process followed to obtain a radiological map of Catalonia (Spain). The mobile unit consists of two 2”x2” LaBr₃ scintillation detectors mounted on the top of a 4x4 car. To obtain the preliminary map, the extension of Catalonia was divided in 1425 cells of 5x5 km². Before starting the measurements, we planned a route to ensure a proper distribution and a minimum quantity of spectra within each cell. The car is equipped with a portable computer to control spectra acquisition and a GPS system that associates a position to each spectrum. Each spectrum is stabilised and calibrated. During the acquisition, the computer placed inside the car shows, in real-time, the value of the ambient dose equivalent and the exact location. Therefore, when the software obtains an unexpected high value, the driver of the car can modify the route to acquire more spectra of the area. The first data set of measurements included 70000 spectra obtained during stable weather conditions and represent the preliminary results of the radiological map, as other data campaigns are currently under preparation. In this study, we present the ambient dose equivalent map of Catalonia and isotopic information of interest, such as punctual detections of ¹³⁷Cs and ¹³¹I and other radionuclides. The origin of these detections is analysed and explained in detail.

How to cite: Prieto, E., Cerezo, A., Reichardt, I., and Salvadó, M.: Mapping the environmental radioactivity in Catalonia using a mobile unit with LaBr3 scintillation detectors., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12190, https://doi.org/10.5194/egusphere-egu23-12190, 2023.

Detection of gamma-rays emitted by K-40 decay demonstrates potential for reliable soil moisture estimation for agricultural and hydrological applications. With a circular footprint of roughly 20 m radius, gamma-ray spectroscopy (GRS) provides a continuous, non-invasive average measurement that fills the scale gap between point and satellite data. GRS sensors have also been successfully integrated with Unmanned Aerial Systems opening the potential for soil moisture mapping.  Current theoretical models of gamma-ray spectra and soil moisture have not been extensively tested with empirical data. An existing soil moisture model for NaI gamma-ray spectra includes a method for biomass water content correction and was tested with five sampling campaigns in a tomato field, while another soil moisture model was tested with a single sampling campaign in a sugar beet field using CsI gamma-ray spectra. We hypothesize that testing existing theoretical models with thorough empirical data over a range of soil moisture and vegetative conditions will increase our understanding of the relationship between gamma-ray spectra, soil moisture, and biomass, and will allow us to validate and/or improve the soil moisture calibration function.

In this study we conduct a robust calibration of a stationary CsI gamma-ray soil moisture sensor (gSMS, Medusa Radiometrics) against gravimetric water content samples at a long term agricultural experimental field in eastern Nebraska, United States. Additional measurements include an Eddy Covariance tower, a Cosmic-Ray Neutron Sensor, in-situ soil moisture sensors, and destructive vegetation sampling every 10 days during the growing season. In total, 18 sampling campaigns were conducted between June 2021 and October 2022 under bare soil, maize, and soybean conditions. Soil samples were collected in a radial pattern at 0, 2, 5, and 12 m from the sensor, every 60 degrees following the expected spatial sensitivity of the gSMS. Samples from the 19 locations surrounding the sensor were aggregated in 5 cm intervals from 0 to 35 cm depth. Both a depth-weighting function and the arithmetic mean were used to calculate the average gravimetric water content within the sensing volume.

We then leverage the relatively large experimental data set of gravimetric water content and K-40 counts to test current theoretical approaches to soil moisture estimation with GRS. Data from both bare soil and vegetated conditions allow us to investigate and potentially remove the biomass water content signal from the soil moisture estimation. Comparison with the existing theoretical calibration functions shows large deviations with the empirical data.  Cosmic-ray Neutron Sensor data recorded at the site shows a high degree of correlation (R > 0.7 for hourly data) between the K-40 counts and neutron counts under changing biomass conditions. Lastly, comparison of the GRS derived soil moisture data with the in-situ soil moisture sensors, rainfall, and evapotranspiration result in good correspondence with soil moisture state and water fluxes at the study site.

How to cite: Becker, S. M. and Franz, T. E.: Theoretical vs experimental relationship between K-40 counts and gravimetric water content at a well instrumented agricultural research station in Nebraska, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7988, https://doi.org/10.5194/egusphere-egu23-7988, 2023.