Fig. 1

Diagram of factors governing indoor radon concentrations and exposure^a. ^aThis diagram was modified from Font [5] and Font and Baixeras [6]. Radon in the soil permeates a building: diffusive and advective flow; radon from BM diffuses into buildings. A building’s water supply and natural gas are also sources that introduce radon into a building, although that from natural gas is not generally considered because it is difficult to measure and contributes to only very small concentrations. Additionally, indoor radon concentrations can also vary as a result of air exchange between indoor and outdoor air. Therefore, a subject’s indoor radon exposure in a building can be mainly determined by his or her behaviour and indoor radon concentration of the building that he or she resides