Radon concentrations in the 1998 norwegian housing stock

A nation-wide survey of radon concentrations in Norwegian dwellings was undertaken in the period 1987 - 89. In this survey, radon measurements were made by CR-39 etched track detectors (six months integration time) in the main bedroom of approximately 7500 randomly selected dwellings built before 1980. The annual average radon concentration in Norwegian bedrooms was calculated to 51 Bq/m3, and 3.7 % of the results exceeded 200 Bq/m3. In a large proportion of single-family houses (including detached, semi-deached, row and terraced houses), the living room and the kitchen are located on the ground floor while the bedrooms are on the first floor. In most cases the radon concentration is higher on the ground floor than on the first floor, and there may also be differences between bedrooms and other rooms on the same floor owing to different ventilation conditions/habits. An additional factors that could have influenced the measurements was that the winters from 87 to 89 were considerably warmer than normal. Based on these considerations, the annual average radon concentration in Norwegian dwellings was estimated to be between 55 and 65 Bq/m3 ?1??and it was further estimated that approximately 5 % of the housing stock exceeds 200 Bq/m3. In this paper, the results of the nation-wide survey will be compared with results of follow-up surveys in approximately 5000 randomly selected dwellings from 31 out of the total 430 municipalities. These 31 municipalities covers 7% of the Norwegian population. The measurements were made by CR-39 etched track detectors and one or two detectors were placed in each dwelling for a period of two to three months in the heating season (october to april). The population weighted,average radon concentration during the measurement period was calculated to 149 Bq/m3, and the annual average concentration was estimated to 112 Bq/m3 compared to 54 Bq/m3 for the same municipalities in the nation-wide survey. By using the same ratio for the whole country, the annual average concentration in Norwegian dwellings was estimated to 106 Bq/m3. It was further estimated that approximately 10% of the housing stock exceeds 200 Bq/m3. The difference between the nation-wide survey and the present results will be discussed in more detail in this paper.