Distributions of airborne radon concentrations in Seoul metropolitan subway stations

Airborne 222Rn concentrations were surveyed to observe daily and seasonal variations in the 74 subway stations in the Seoul metropolitan area. Each station built of concrete elements usually has two or three stories underground with natural and mechanical ventilation facilities. The airborne radon level was determined three times: in July and August 1989, in January 1990, and in February 1991. Each study duration varied from 1-4 wk. The resulting distribution of annual average radon concentration in underground platforms was characterized by a geometric mean of 93 Bq m-3. Radon levels varied within a wide range from undetectable to 677 Bq m-3 in stations. In addition to the study of short- and long-term radon variation, various environmental factors having an influence on radon level were studied in order to obtain indications of the possible radon sources.