Indoor radon is a major hazard to human health; it is one of the leading causes of lung cancer. Therefore, radon research in Asia has intensified recently due to the growing awareness of the harm that radon poses. An analysis of the collected literature data showed that in Asia–Oceania, some regions have—or are believed to have—little indoor radon problems due to climate and low Rn ground. It can be concluded that countries have their own approaches, techniques, and protocols. Data were not harmonized within each region; however, measurement techniques were compared by regional intercomparison exercises. The situation differs regarding studies on the usability of radon as a tracer or potential predictor of tectonic phenomena, as some countries are in seismically active zones, such as India, Taiwan, China, Japan, etc. India and Taiwan are global leaders in this research, as well as Italy, which is another seismically affected country. We provide an overview of radon-related surveying and research activities conducted in the western, southern, and eastern Asian regions over the past few years. Additionally, we observed that the number of indoor radon measurements per million inhabitants increases as the human development index (HDI) increases.

<p>Exposure to indoor radon (Rn) is recognized as a health hazard which may cause several 100,000 lung cancer fatalities per year world-wide. Physical causes are Rn generation as part of the decay chains that originate in ubiquitous uranium and thorium and its transport through the natural to the built environment, where it can infiltrate indoor air. Generation and transport of Rn constitute geogenic Rn hazard. Its geographical distribution reflects the ones of the properties of the media in which the processes occur, namely their geochemistry and physical properties such as porosity, permeability and humidity. By linking to measured indoor Rn concentration, geogenic hazard can be transformed into the expected indoor Rn concentration in a hypothetical house at a location or the probability that in the house a Rn threshold is exceeded.</p><p>Hazard turns into risk if somebody is exposed to the hazardous agent. Given a certain amount of hazard, the risk results from conditions which enable exposure (defining vulnerability and susceptibility to the hazard) and the presence of people who are actually exposed. While hazard yields a probability that somebody exposed suffers a detriment, risk quantifies the size of the detriment, e.g. the expected number of Rn induced lung cancer fatalities per unit area. Elevated risk can occur also if the individual probability of detriment is low, if the number of exposed persons is high.</p><p>Rn abatement policy which through regulation aims to reduce the detriment, should respond differently to hazard and risk. In the former case, it should reduce the probability of individual high exposure occurring, by remediation, or avoiding it to occur, by preventive action. Responding to the latter means reducing collective exposure.</p><p>So far, policy has mainly focused on the first, i.e. hazard reduction, while comparatively less attention has been given to the second, although the overall detriment to society depends on it. Although Rn regulation has already been developed extensively in Europe, discussion of the aspect of collective risk reduction seems to be in the beginning only.</p><p>In this presentation, we outline the problem by showing the difference between hazard and risk and addressing existing Rn abatement strategies.</p>

Radon abatement policy is the response to the detrimental effect of indoor radon which is estimated to cause hundred thousands of lung cancer fatalities worldwide annually. The policy consists of decisions to implement measures. Decisions rest on data and (sometimes competing) interests, among them health protection. Its weight as an argument depends, among other factors, on knowledge about its subject – in this case, levels, effects, and geographical distribution of exposure to radon. Therefore, the quality assurance of radon policy depends on one of the underlying knowledge, from data to decisions derived from them. Some aspects of the quality assurance chain are discussed in this article.

<p>Radium-226, part of the <sup>238</sup>U decay chain, which is ubiquitous in the ground, generates a terrestrial gamma ray field which can be detected above ground, through its strongly gamma radiating progeny <sup>214</sup>Bi and <sup>214</sup>Pb and to minor degree through <sup>226</sup>Ra itself. The measurand is ambient dose equivalent rate, ADER, nSv/h, that also includes contribution from cosmic rays and other terrestrial radionuclides (i.e. <sup>40</sup>K and <sup>232</sup>Th decay chain). On the other hand, its decay produces <sup>222</sup>Rn (here shortly Rn) which can migrate through the ground and lead to measurable Rn concentration (Bq/m³) in ambient media, namely soil, ground water and the indoor and outdoor atmosphere. One can therefore expect that originating from the same source, ADER and Rn are statistically related and ADER may serve as predictor of Rn related quantities, such as mean Rn concentration over an area, its probability to exceed a level or the status of an area as radon priority area. However, as the pathway from Ra in the ground to ambient Rn is complex, and as measured ADER has also other contributions than Ra, the relation must be expected to be blurred by nuisance factors, which pose a challenge to analysis.</p> <p>A large and ever increasing dataset of ADER is freely available from the Citizen Science project Safecast [1], founded in Japan after the Fukushima accident 2011. It has since spread over the entire world (with measurements in regionally very different density, though) and by late 2022, the dataset comprised 180M measurements, of which about 50M in Europe. The measurements were performed with a standard instrument called bGeigie nano, of which several 1000 circulate around the globe, used by voluntary citizen scientists who send their data to Safecast. On the other hand, in Europe a good indoor Rn concentration (IRC) database is available, based on about 1.2M individual measurements [2], as well as an interpolated European IRC map [3].</p> <p>Thus, we relate ADER (Safecast) with IRC and derived quantities, both aggregated on a common 10 km × 10 km grid. Raw ADER is reduced by cosmic dose rate (related to altitude a.s.l., accessible from digital elevation database) and mean internal detector background. Since it can be assumed that ADER on a point depends on its urbanization status (due to the influence of building materials which also contain gamma radiating nuclides), this factor is also investigated. </p> <p>First results are promising and will be shown in the presentation.</p> <p> </p> <p>[1] https://safecast.org/</p> <p>[2] European Commission, Joint Research Centre – Cinelli, G., De Cort, M. & Tollefsen, T. (Eds.), European Atlas of Natural Radiation, https://remon.jrc.ec.europa.eu/About/Atlas-of-Natural-Radiation/Download-page</p> <p>[3] Elío J., et al. (2019): The first version of the Pan-European Indoor Radon Map. Nat. Hazards Earth Syst. Sci., 19, 2451–2464, https://doi.org/10.5194/nhess-19-2451-2019</p>

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