Comparative temporal behavior of radon- and thoron-progeny in surface air over the midwestern U.S

Temporal variations in airborne 210Pb, 212Pb, 214Pb, 218Po, and 214Bi concentrations at Springfield, Missouri, USA, are compared with each other and with results reported from studies performed in other parts of the world. At Springfield diurnal concentration patterns of 210Pb are similar to those of 212Pb, but seasonal concentration patterns differ markedly. Additionally, abnormal disequilibrium conditions are sometimes found to exist in Springfield among 218Po, 214Pb, and 214Bi in which progeny/parent ratios are greater than 1. Findings similar to those presented here have been reported at some sites throughout the world, but different temporal patterns have been reported at others. Examination of concentration dependence on meteorological conditions at Springfield indicates that some of these differences are correlated with temperature and ground snow cover. Implications of these findings for use of thoron- and radon-progeny as atmospheric tracers are discussed. (author)