ANNUAL AVERAGE AND SEASONAL VARIATIONS OF RESIDENTIAL RADON CONCENTRATION FOR ALL THE ITALIAN REGIONE

A representative National Survey to evaluate the exposure to natural sources of ionizing radiation in dwellings was conducted in all the 21 Italian Regions from 1989 to 1998, and the complete results are reported in this paper. Radon concentration was measured for two consecutive 6-month periods (generally covering the spring–summer and autumn–winter seasons) in one room, usually the main bedroom, of each surveyed dwelling. Validated radon concentration measurements were obtained for a total of 5631 dwellings, distributed in 232 towns (all the 50 towns with more than 100,000 inhabitants and 182 randomly sampled smaller towns). The national average, weighted by the population of each Region, of the annual radon concentration is View the MathML source, the geometric mean is View the MathML source, and the geometric standard deviation is 2.1. The fraction of dwellings with a radon concentration exceeding the reference levels of 150, 200, 400, and View the MathML source are 7.7%, 4.1%, 0.9%, and 0.2%, respectively. Regional averages ranged from about View the MathML source to about View the MathML source. The uncertainty of regional values can be relevant in the case of small Regions, where few small towns were sampled, however such uncertainties do not affect national values significantly. A log-normal model underestimates the fraction of dwellings with high radon concentration and needs to be adjusted to obtain a better fitting. Two complete 6-month measurements were obtained for 4742 dwellings. The regional values of the geometric mean and of the geometric standard deviation of the winter/summer ratio ranged from 0.81 to 2.58 and from 1.32 to 1.88, respectively. The corresponding national values were 1.23 and 1.71, respectively. These results and their implications are discussed in the paper.