Annual and seasonal variations of indoor radon concentration in Skopje (Republic of Macedonia)

This paper presents the results of a survey of indoor radon concentrations in the dwellings of 10 Municipalities in the Skopje: the capital and the largest city of the Republic of Macedonia (600 000 habitants). The indoor radon concentrations were measured during the four successive seasons from December 2008 to December 2009 using integrating passive alpha track-etch detectors with an exposure period of three months. The annual mean indoor radon concentration in each measuring site was estimated as an arithmetic mean from the four individual measurements. The measurements were completed for 124 dwellings, of which 112 dwellings revealed indoor radon concentrations lower than 200 Bq m−3, and 3 showed radon concentrations in excess of 400 Bq m−3. The annual mean indoor radon concentrations were found to be log-normally distributed, ranging from 18 to 502 Bq m−3. The geometric mean value of the indoor radon concentration in Skopje region was estimated to be 83*/1.94 Bq m−3. The results of analysis of variance showed statistically significant differences among annual mean values of the indoor radon concentrations of among the different municipalities (p=0.021). The influence of the factors linked to building characteristics in relation to the annual mean of indoor radon concentration was also a subject to examination. The factors which allow differentiation into subgroups (significance level p<0.05) were: the floor level (p<0.0001), presence of basement (p<0.0001), and type of heating (p=0.004). Seasonal dependence of indoor radon concentration was observed. The minimum indoor radon concentrations were found in the summer season whereas maximum levels were observed in the winter season (p< 0.0001)