Analysis of the spatial variation of indoor radon concentrations (national survey in Bulgaria)

Indoor Radon Concentrations in Severe Cold Area and Cold Area and Impact of Energy-saving Design on Indoor Radon in China

ABSTRACT

This study investigated indoor radon concentrations in modern residential buildings in the Cold Area and Severe Cold Area in China. A total of 19 cities covering 16 provinces were selected with 1,610 dwellings measured for indoor radon concentration. The arithmetic mean and geometric mean of indoor radon concentration were 68 Bq m-3 and 57 Bq m-3, respectively. It was found that indoor radon concentrations were much higher in the Severe Cold Area than those in the Cold Area. The indoor radon concentrations showed an increasing trend for newly constructed buildings. It was estimated that the average effective dose from inhalation of indoor radon is 2.15 mSv and 1.60 mSv for the Severe Cold Area and Cold Area, respectively. The more and more rigid energy-saving design for residential buildings in the Severe Cold Area and Cold Area has an obvious impact on the increased trend of indoor radon due to extremely low air exchange rate in China.

Exploring statistical and machine learning techniques to identify factors influencing indoor radon concentration

Radon is a radioactive gas with a carcinogenic effect. The malign effect on human health is, however, mostly influenced by the level of exposure. Dangerous exposure occurs predominantly indoors where the level of indoor radon concentration (IRC) is, in its turn, influenced by several factors. The current study aims to investigate the combined effects of geology, pedology, and house characteristics on the IRC based on 3132 passive radon measurements conducted in Romania. Several techniques for evaluating the impact of predictors on the dependent variable were used, from univariate statistics to artificial neural network and random forest regressor (RFR). The RFR model outperformed the other investigated models in terms of R2 (0.14) and RMSE (0.83) for the radon concentration, as a dependent continuous variable. Using IRC discretized into two classes, based on the median (115 Bq/m3), an AUC-ROC value of 0.61 was obtained for logistic regression and 0.62 for the random forest classifier. The presence of cellar beneath the investigated room, the construction period, the height above the sea level or the floor type are the main predictors determined by the models used.

Indoor radon concentration in state schools of four Bulgarian districts

Indoor radon concentrations were surveyed in 230 public schools in four Bulgarian districts for the period November/December 2019 to May/June 2020. The measurements were carried out in 2427 rooms on the basement, ground floor and first floor using the passive track detectors of the Radosys system. The estimated arithmetic and geometric means with standard deviations were 153 ± 154 and 114 Bq/m3 (geometric standard deviation (GSD) = 2.08), respectively. The results are higher than those referred from the National Radon Survey in dwellings. In 9.4% of the rooms, the radon concentrations were above the reference value of 300 Bq/m3. The difference between indoor radon concentrations in the districts was significant, which proves its spatial variation. The hypothesis that the applied energy efficiency measures increase indoor radon values in buildings was confirmed. The surveys demonstrated the importance of indoor radon measurements in school buildings, in order to control and reduce children's exposure.

Assessment of indoor radon exposure in South Korea

The objective of this study is to update the national and regional indoor radon concentrations in South Korea and assess indoor radon exposure. Based on the previously published survey results and the collected measurement data of surveys conducted since 2011, a total of 9271 indoor radon measurement data covering 17 administrative divisions are finally used for analysis. The annual effective dose from the indoor radon exposure is calculated using dose coefficients recommended by the International Commission on Radiological Protection. The population-weighted average indoor radon concentration was estimated to be a geometric mean of 46 Bq m^-3(GSD = 1.2) with 3.9% of all samples showing values exceeding 300 Bq m^-3. The regional average indoor radon concentration ranged from 34 to 73 Bq m^-3. The radon concentrations in detached houses were relatively higher than those in public buildings and multi-family houses. The annual effective doses to the Korean population due to indoor radon exposure were estimated to be 2.18 mSv. The updated values in this study might better represent the national indoor radon exposure level in South Korea because they contain more samples and cover a wider range of geographical areas than previous studies.

Diurnal, monthly, and seasonal variations of indoor radon concentrations concerning meteorological parameters

As reported by the Turkish Atomic Energy Agency (formerly TAEK, newly TENMAK), Izmir province has higher indoor radon concentrations compared to other cities in Turkey. Since modern people spend 92% of their daily time indoors, it is important to know indoor radon levels and long-term variation. However, our knowledge of indoor radon levels of Izmir and its surrounding are limited. Moreover, there is no information about this area's large-term variation of indoor radon. In this study, which was carried out with this motivation, indoor radon concentrations and meteorological parameters were measured in an office of the teaching staff in a university building. Data were collected hourly over 25 months (762 days). Raw data, diurnal, monthly, and seasonal variations of parameters were investigated separately. The results show that the average indoor radon concentration (18 Bq m^-3) is relatively lower than national and international reference values. Indoor radon concentrations showed an increasing and decreasing trend throughout the day. Radon concentrations are slightly higher in the morning (downtime and early hours of the day) and then reduced in the afternoon. This can be related to the daily routine usage of the office, which is affected by ventilation of the room, air temperature variations, etc.

Temporal uncertainty versus coefficient of variation for rational regulation of indoor radon

Significant temporal variations of radon and other air pollutants can be observed in any room, even one with permanently closed windows and doors. Therefore, a question arises: how can one assess the conformity of a room with a normative and make a reliable decision if the test lasts <1 year (days or months)? The measurement protocol fundamentally differs between Europe with its long-term testing tradition lasting several months, and the US where short-term tests of several days are more common. Neither the European nor the American protocols considers the temporal uncertainty of indoor radon, a factor that usually exceeds the instrumental uncertainty (including in long-term tests) and is 2-3 times higher the coefficient of variation (COV) commonly used to estimate temporal variations. This problem significantly complicates the creation of a rational and harmonized ISO standard. At the same time, strict adhering to the fundamental ISO/IEC rules within such concepts as "measurement uncertainty" and "conformity assessment" allows to control the coverage probability or reliability of decision making. Within ISO/IEC, proposed are a criterion of conformity assessment of a room with a normative for both short- and long-term measurements, as well as a statistical algorithm for determining the temporal uncertainty considering mode and measurements duration.

A model comparison of diffusion-controlled radon exhalation from solid and cavity walls with application to high background radiation areas

Radon exhaled from building material surfaces is an important source of indoor radon. Yangjiang, located in the southern part of mainland China, is well-known as a high background radiation area (HBRA). Rather, high levels of radon and thoron concentration have been observed in adobe and brick houses. Reducing the indoor radon concentration remains an important issue in the high background radiation areas of China and the world. Generally, the walls of Chinese dwellings are solid. In this paper, a simple one-dimensional model for predicting the radon diffusion in a cavity wall is proposed, and an analysis formula describing the radon exhalation rate from cavity wall surfaces is presented. The influence on the radon exhalation rate due to leakage through structural joints and building material cracks is analyzed. The simulation results indicate that the radon exhalation rate from a cavity wall surface is far lower than that from a solid wall. The structure of cavity walls themselves is therefore useful as a mechanism for reducing the indoor radon in high background radiation areas across the world.

Importance of Discriminative Measurement for Radon Isotopes and Its Utilization in the Environment and Lessons Learned from Using the RADUET Monitor

Radon (222Rn) and thoron (220Rn), sources of natural background radiation, have been the subjects of long-standing studies, including research into radon and thoron as major causes of lung cancer at domestic and international levels. In this regard, radon and thoron measurement studies have been widely conducted all over the world. Generally, the techniques used relate to passive nuclear track detectors. Some surveys have shown that passive monitors for radon are sensitive to thoron, and hence some measured results have probably overestimated radon concentrations. This study investigated radon and thoron measurements in domestic and international surveys using the passive radon-thoron discriminative monitor, commercially named RADUET. This paper attempts to provide an understanding of discriminative measurements of radon isotopes and to present an evidence-based roadmap.

Modelling of the temporal indoor radon variation in Bulgaria

In this study, temporal variations of indoor radon concentrations in Bulgaria were investigated. The radon concentrations were measured by nuclear track detectors as part of the Bulgarian National Survey, performed in the dwellings of 28 regional districts. The detectors were exposed through a year in two consecutive time periods of different lengths. For 2433 dwellings, measurements could be completed for both time periods, while for 345 dwellings they could only be completed for one of the periods. To estimate any missing radon concentrations, a temporal correction procedure was developed. This procedure, which included development of a linear correlation between the ln-transformed radon concentrations from the 9-month period [CRn(L)] and from the 3-month period [CRn(S)]. A normal distribution of the data, which is a condition for linear regression, was achieved when the ln-transformed radon concentrations were grouped by climate zone, then by regional districts, and finally by the presence/absence of a basement in the investigated building. The linear models obtained for each group showed reasonable coefficients of determination (R² ≈ 0.50) and root mean square errors (RMSEs) of about 0.50. When these correlations were used to reconstruct radon concentrations in missing measurement periods, it turned out that the reconstructed data (for 345 dwellings) were within the 95% confidence interval of the measured data (for 2433 dwellings). The geometric means of CRn(L) and CRn(S) were 76 Bq/m³ and 100 Bq/m³, respectively, for 2433 dwellings, which are almost equal to those of 75 Bq/m³ and 98 Bq/m³, which represent the measured and reconstructed data together (for 2778 dwellings).