Indoor 222Rn measurements in the region of Beijing, People's Republic of China.

Passive integrating activated C detectors were used to study the regional distribution and temporal variation of 222Rn in indoor air in dwellings in the Beijing region. Measurements were made in 537 dwellings, which were either detached houses or multi-family apartments. The city-wide study was completed in 1985. The distributions are approximately log-normal with 90% of the dwellings having 222Rn levels less than 60 Bq m-3. The weighted average 222Rn concentration has been found to be 22.4 Bq m-3. Averages for detached houses and multi-family dwellings are 25.9 and 15.2 Bq m-3, respectively. Assuming an equilibrium factor of 0.5 and an occupancy factor of 0.8, the average equilibrium equivalent concentration of 222Rn progeny is 11.2 Bq m-3 and the annual average effective dose equivalent is 1.1 mSv.