title: Major influencing factors of indoor radon concentrations in Switzerland.
abstract: OBJECTIVE
  In Switzerland, nationwide large-scale radon surveys have been conducted since the early 1980s to establish the distribution of indoor radon concentrations (IRC). The aim of this work was to study the factors influencing IRC in Switzerland using univariate analyses that take into account biases caused by spatial irregularities of sampling.
  
  
  METHODS
  About 212,000 IRC measurements carried out in more than 136,000 dwellings were available for this study. A probability map to assess risk of exceeding an IRC of 300 Bq/m(3) was produced using basic geostatistical techniques. Univariate analyses of IRC for different variables, namely the type of radon detector, various building characteristics such as foundation type, year of construction and building type, as well as the altitude, the average outdoor temperature during measurement and the lithology, were performed comparing 95% confidence intervals among classes of each variable. Furthermore, a map showing the spatial aggregation of the number of measurements was generated for each class of variable in order to assess biases due to spatially irregular sampling.
  
  
  RESULTS
  IRC measurements carried out with electret detectors were 35% higher than measurements performed with track detectors. Regarding building characteristics, the IRC of apartments are significantly lower than individual houses. Furthermore, buildings with concrete foundations have the lowest IRC. A significant decrease in IRC was found in buildings constructed after 1900 and again after 1970. Moreover, IRC decreases at higher outdoor temperatures. There is also a tendency to have higher IRC with altitude. Regarding lithology, carbonate rock in the Jura Mountains produces significantly higher IRC, almost by a factor of 2, than carbonate rock in the Alps. Sedimentary rock and sediment produce the lowest IRC while carbonate rock from the Jura Mountains and igneous rock produce the highest IRC. Potential biases due to spatially unbalanced sampling of measurements were identified for several influencing factors.
  
  
  CONCLUSIONS
  Significant associations were found between IRC and all variables under study. However, we showed that the spatial distribution of samples strongly affected the relevance of those associations. Therefore, future methods to estimate local radon hazards should take the multidimensionality of the process of IRC into account.
authors: Institute of Radiation Physics, University Hospital Center of Lausanne (CHUV), Rue du Grand-Pré 1, 1007 Lausanne, Switzerland. Electronic address: georg.kropat@chuv.ch.
authors: Georg
authors: G
authors: Kropat
authors: Institute of Radiation Physics, University Hospital Center of Lausanne (CHUV), Rue du Grand-Pré 1, 1007 Lausanne, Switzerland.
authors: Francois
authors: F
authors: Bochud
authors: Center for Research on Terrestrial Environment, University of Lausanne, Quartier UNIL-Mouline, 1015 Lausanne, Switzerland.
authors: Michel
authors: M
authors: Jaboyedoff
authors: Institute of Radiation Physics, University Hospital Center of Lausanne (CHUV), Rue du Grand-Pré 1, 1007 Lausanne, Switzerland.
authors: Jean-Pascal
authors: JP
authors: Laedermann
authors: Swiss Federal Office of Public Health, Schwarzenburgstrasse 165, 3003 Berne, Switzerland.
authors: Christophe
authors: C
authors: Murith
authors: Swiss Federal Office of Public Health, Schwarzenburgstrasse 165, 3003 Berne, Switzerland.
authors: Martha
authors: M
authors: Palacios
authors: Institute of Radiation Physics, University Hospital Center of Lausanne (CHUV), Rue du Grand-Pré 1, 1007 Lausanne, Switzerland.
authors: Sébastien
authors: S
authors: Baechler
mesh_terms: D000396:Air Pollutants, Radioactive / Q000032:analysis*; D016902:Air Pollution, Indoor / Q000032:analysis*; D000531:Altitude; D003252:Construction Materials; D055593:Geological Phenomena; D006798:Housing; D011834:Radiation Monitoring; D011886:Radon / Q000032:analysis*; D012574:Schools; D013557:Switzerland; D013696:Temperature
chemical_list: D000396:Air Pollutants, Radioactive; D011886:Radon
keywords: Building characteristics; Indoor radon; Lithology; Outdoor temperature; Univariate analysis