Atmospheric stability effects on potential radiological releases at a nuclear research facility in Romania: Characterising the atmospheric mixing state

Meteorological Approach in the Identification of Local and Remote Potential Sources of Radon: An Example in Northern Iberian Peninsula

This paper presents a meteorological approach to identify local and remote sources driving the variability of surface daily radon concentrations. To this purpose, hourly ²²²Rn concentration and surface meteorological measurements, and air mass trajectories at Bilbao station (northern Iberian Peninsula) during the period 2017-2018 have been taken as reference. To investigate the potential transport pathways and potential ²²²Rn sources, the backward trajectory cluster analysis, trajectory sector analysis (TSA), and potential source contribution function (PSCF) are applied. On average, the diurnal ²²²Rn cycle shows the expected behaviour, with larger concentrations during the night and minimum concentrations during the daylight hours, with differences in the seasonal amplitudes. According to daily differences between maximum and baseline values, ²²²Rn daily cycles were grouped into six groups to identify meteorological conditions associated with each amplitude, and potential source areas and transport routes of ²²²Rn over Bilbao. The trajectory cluster and the TSA method show that the main airflow pathways are from the south, with small displacement, and the northeast, while the analysis of surface wind speed and direction indicates that the highest amplitudes of ²²²Rn concentrations are registered under the development of sea-land breezes. The PSCF method identified south-western and north-eastern areas highly contributing to the ²²²Rn concentration. These areas are confirmed by comparing with the radon flux map and the European map of uranium concentration in soil. The results have demonstrated the need in combining the analysis of local and regional/synoptic factors in explaining the origin and variability of ²²²Rn concentrations.

Outdoor Radon as a Tool to Estimate Radon Priority Areas-A Literature Overview

Doses from the exposure to outdoor radon are typically an order of magnitude smaller than those from indoor radon, causing a greater interest on investigation of the latter for radiation protection issues. As a consequence, assessment of radon priority areas (RPA) is mainly based on indoor radon measurements. Outdoor radon measurements might be needed to guarantee a complete estimation of radiological risk and may help to improve the estimation of RPA. Therefore, authors have analysed the available literature on outdoor radon to give an overview of outdoor radon surveys and potential correlation with indoor radon and estimation of RPA. The review has shown that outdoor radon surveys were performed at much smaller scale compared to indoor radon. Only a few outdoor radon maps were produced, with a much smaller density, covering a larger area, and therefore putting doubt on the representativeness of this data. Due to a large variety of techniques used for outdoor radon measurements and requirement to have detectors with a high sensitivity and resistance to harsh environmental conditions, a standardised measurement protocol should be derived. This is no simple endeavour since there are more applications in different scientific disciplines for outdoor radon measurements compared to indoor radon.

Online monitoring of lead-214 (214Pb) on atmospheric aerosols by low-resolution gamma-ray spectrometry

This paper provides a new approach that simplifies the monitoring of ²¹⁴Pb activity concentration on aerosols in the atmospheric surface layer. The approach allows obtaining data on ²¹⁴Pb activity concentration with the discreteness of 2 h. The experimental setup described in the paper made it possible to achieve a minimum detectable activity level of 0.4 Bq m^-3. Using this approach, the data on the diurnal variability of ²¹⁴Pb activity concentration in the atmosphere of Sevastopol city for a period of 18 months were obtained. The ²¹⁴Pb activity concentration varied from < 0.4 (less than 1% of the data series) to 8.9 Bq m^-3, mean value 2.0 ± 1.0 Bq m^-3. The analysis of the temporal variability of ²¹⁴Pb activity concentration on different time scales (diurnal, seasonal) was carried out. Annually averaged diurnal variation curve of ²¹⁴Pb activity concentration showed a peak at 6:00 local time and a minimum at 18:00. The maximum variability in the seasonal averaged diurnal cycle of ²¹⁴Pb activity concentration is observed in summer (± 30% of the daily average value) and the minimum in winter (± 13%). The maximum seasonal average value of ²¹⁴Pb activity concentration is observed in winter (2.5 Bq m^-3) and the minimum in summer (1.4 Bq m^-3). A quantitative estimate of the annual effective dose due to exposure to outdoor radon was obtained by using ²¹⁴Pb data, and it was 0.03 mSv a^-1.

Radon-based atmospheric stability classification in contrasting sub-Alpine and sub-Mediterranean environments

A recently-developed radon-based technique is used to investigate relative changes in summertime atmospheric stability at two sites in Slovenia with contrasting geographical settings. Although atmospheric stability for both sites (50 km apart) was shown to be governed by similar synoptic conditions, their contrasting settings caused differences in mixing conditions for each stability category. At the urban sub-Alpine site Ljubljana, situated within a topographic basin, wind speeds associated with the most stable conditions were 0.2-0.3 m s^-1. By comparison, corresponding wind speeds for the near-coastal sub-Mediterranean site Ajdovščina, located at the foothills of the Trnovski gozd barrier, were 0-0.2 m s^-1. The wind direction at Ljubljana under stable conditions (∼80°) was consistent with drainage flow into the basin along the Sava River valley. The corresponding wind direction at Ajdovščina was 20-40°, consistent with gentle katabatic drainage from the flanks of the Trnovski gozd barrier. After removing fetch effects on radon variability at each site, a large contrast in local contributions to the radon signal was noted: the diurnal amplitude of the local radon signal increased from ∼24 Bq m^-3 at Ljubljana to ∼47 Bq m^-3 at Ajdovščina. This difference was attributed to a greater nocturnal radon accumulation rate at Ajdovščina (3.5 Bq m^-3 h^-1 vs 2.1 Bq m^-3 h^-1) due to higher radon fluxes from flysch and carbonate rocks compared to the sea and lake sediments in the Ljubljana Basin. The ability of radon to consistently distinguish subtle changes in atmospheric mixing at sites with contrasting topographic settings indicates that it will be a powerful tool for characterising air quality in these complex environments. Specifically, diurnal radon cycles indicate that the capability of the atmosphere to dilute primary pollutants is considerably less in the basin environment.

Skill-Testing Chemical Transport Models across Contrasting Atmospheric Mixing States Using Radon-222

We propose a new technique to prepare statistically-robust benchmarking data for evaluating chemical transport model meteorology and air quality parameters within the urban boundary layer. The approach employs atmospheric class-typing, using nocturnal radon measurements to assign atmospheric mixing classes, and can be applied temporally (across the diurnal cycle), or spatially (to create angular distributions of pollutants as a top-down constraint on emissions inventories). In this study only a short (<1-month) campaign is used, but grouping of the relative mixing classes based on nocturnal mean radon concentrations can be adjusted according to dataset length (i.e., number of days per category), or desired range of within-class variability. Calculating hourly distributions of observed and simulated values across diurnal composites of each class-type helps to: (i) bridge the gap between scales of simulation and observation, (ii) represent the variability associated with spatial and temporal heterogeneity of sources and meteorology without being confused by it, and (iii) provide an objective way to group results over whole diurnal cycles that separates ‘natural complicating factors’ (synoptic non-stationarity, rainfall, mesoscale motions, extreme stability, etc.) from problems related to parameterizations, or between-model differences. We demonstrate the utility of this technique using output from a suite of seven contemporary regional forecast and chemical transport models. Meteorological model skill varied across the diurnal cycle for all models, with an additional dependence on the atmospheric mixing class that varied between models. From an air quality perspective, model skill regarding the duration and magnitude of morning and evening “rush hour” pollution events varied strongly as a function of mixing class. Model skill was typically the lowest when public exposure would have been the highest, which has important implications for assessing potential health risks in new and rapidly evolving urban regions, and also for prioritizing the areas of model improvement for future applications.

Radon-222 related influence on ambient gamma dose

Ambient gamma dose, radon, and rainfall have been monitored in southern Bucharest, Romania, from 2010 to 2016. The seasonal cycle of background ambient gamma dose peaked between July and October (100-105 nSv h^-1), with minimum values in February (75-80 nSv h^-1), the time of maximum snow cover. Based on 10 m a.g.l. radon concentrations, the ambient gamma dose increased by around 1 nSv h^-1 for every 5 Bq m^-3 increase in radon. Radon variability attributable to diurnal changes in atmospheric mixing contributed less than 15 nSv h^-1 to the overall variability in ambient gamma dose, a factor of 4 more than synoptic timescale changes in air mass fetch. By contrast, precipitation-related enhancements of the ambient gamma dose were 15-80 nSv h^-1. To facilitate routine analysis, and account in part for occasional equipment failure, an automated method for identifying precipitation spikes in the ambient gamma dose was developed. Lastly, a simple model for predicting rainfall-related enhancement of the ambient gamma dose is tested against rainfall observations from events of contrasting duration and intensity. Results are also compared with those from previously published models of simple and complex formulation. Generally, the model performed very well. When simulations underestimated observations the absolute difference was typically less than the natural variability in ambient gamma dose arising from atmospheric mixing influences. Consequently, combined use of the automated event detection method and the simple model of this study could enable the ambient gamma dose "attention limit" (which indicates a potential radiological emergency) to be reduced from 200 to 400% above background to 25-50%.

On the relation between outdoor 222Rn and atmospheric stability determined by a modified Turner method

In practice, information about atmospheric stability is often obtained from discrete stability classes determined from routine meteorological observations. However, changing concentrations of the radioactive gas ²²²Rn present in the atmosphere are also considered a good indicator of vertical dispersion and atmospheric stability. A complex, in-depth analysis between these different approaches of atmospheric stability assessment has not been performed so far, and was the main motivation behind this study. The study presents atmospheric radon data measured in Bratislava (Slovakia) and stability indexes (SI) calculated according to a modified Turner method during a period of one year. Basic features of the diurnal and seasonal variations of these variables are discussed. It was found that the time series of radon activity concentration (RAC) lags approximately 5 h behind that of the Turner stability classes adjusted for temperate climate regions. Various time lags were also identified between RAC and meteorological variables used to determine the stability classes. Evaluation of seasonal trends revealed a low variability of mean monthly values of stability classes compared to the variability of mean monthly values of RAC. Another notable difference between RAC and stability indexes was found - while the stability index can both increase and decrease with wind speed, concentration of outdoor radon was never observed to increase with increasing wind speed. In spite of the mentioned discrepancies, the time series of RAC and SI are generally in a good agreement. This is especially true if one compares the deviations of RAC and SI from their mean daily values, when the differences in their seasonal variability are eliminated. Deviations of RAC can be used to calculate diurnal variations of stability indexes. Analysis of a complete year of data also revealed a roughly linear relationship between average values of RAC and calculated stability indexes, because in large datasets random processes tend to cancel each other out.