The ratio of long-lived to short-lived radon-222 progeny concentrations in ground-level air

The ratio of 210Pb air concentration to the short-lived radon (222Rn) decay products concentration at ground level was investigated at a semi-rural location 10 km north of Munich, south Germany, for a period of 11 years (1982–1992). The average ratio from 132 monthly mean values has been found to be (7.5 ± 2.2) × 10−5 (arithmetic mean ± S.D.). While the time series of the short-lived radon daughter concentration exhibit a distinct seasonal pattern with maxima mostly in October of each year, the course of 210Pb air concentration is characterized by high values from October through February. Consequently, high ratios of 210Pb to short-lived decay product concentration are often observed in the winter months of December–February. To study the influence of meteorological conditions on this behaviour, 210Pb and 214Pb concentrations were measured on a short-term basis with sampling intervals of 2–3 days from October 1991 to November 1992. The air concentrations obtained within those intervals were then correlated with actual meteorological parameters. On the base of this investigation the seasonal behaviour can essentially be explained by the more frequent inversion weather conditions in winter than in the summer months. At the same location, the average ratio of 210Po to 210Pb concentration in ground level air has been found to be 0.079 from 459 weakly mean values between 1976 and 1985. Hence, the corresponding average ratios of the short-lived radon daughters (EEC) to 210Pb and 210Po, were 1:7.5 × 10−5 and 1:0.6 × 10−5, respectively.