Comparative temporal behavior of radon- and thoron-progeny in surface air over the midwestern US

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