RESULTS OF THE NATIONAL SURVEY ON RADON INDOORS IN ALL THE 21 ITALIAN REGIONS

The National Survey on Radon Indoors was designed to estimate the distribution of annual radon concentration in Italian dwellings, on the basis of a representative sample of about 5000 dwellings. It started in 1989 and ended in 1994, involving all Italian Regions except Sicilia and Calabria, due to organizational problems in these two regions of Southern Italy. After the official conclusion, two regional surveys were also carried out in Sicilia and Calabria, using the same experimental apparatus and protocols as in the other Regions. The final sample size was of 5631 dwellings distributed in 232 towns, i.e. all the 50 large towns (with more than 100,000 inhabitants) and a random sample of the smaller towns. The results in Sicilia and Calabria were characterized by quite low radon concentrations, thus moving the national radon distribution towards somewhat lower values. The updated national average, weighted by the population of each Region, of the annual radon concentration decreases from 75 Bq/m3 to 70 Bq/m3, the geometric mean decreases from 57 Bq/m3 to 52 Bq/m3, while the geometric standard deviation slightly increases from 2.0 to 2.1. The estimated national average values of the fraction of dwellings with radon concentration above the reference levels of 150 Bq/m3, 200 Bq/m3, 400 Bq/m3, and 600 Bq/m3 are 7.7%, 4.1 % and 0.9%, and 0.2%, respectively. Regional averages range from about 25 Bq/m3 to about 120 Bq/m3. However, th