 At this stage, the predominant residual activity originates from the radon decay product 210Pb, whose half-life (22.3 years) is 2,000 times that of radon (and whose activity is thus 1/2,000 of radon's), and its descendants 210Bi and 210Po.Radon emanation from the soil varies with soil type and with surface uranium content, so outdoor radon concentrations can be used to track air masses to a limited degree.This fact has been put to use by some atmospheric scientists.