Comparison of one- and two-filter detectors for atmospheric 222Rn measurements under various meteorological conditions

Parallel monitoring of 222Rn and its short-lived progeny (218Po and 214Pb) were carried out from November 2007 to April 2008 close to the top of the Schauinsland mountain, partly covered with forest, in South-West Germany. Samples were aspired from the same location at 2.5 m above ground level. We measured 222Rn with a dual flow loop, two-filter detector and its short-lived progeny with a one-filter detector. A reference sector for events, facing a steep valley and dominated by pasture, was used to minimize differences between 222Rn and progeny-derived 222Rn activity concentrations. In the two major wind sectors covered by forest to a distance between 60 m and 80 m towards the station progeny-derived 222Rn activity concentration was on average equal to 87% (without precipitation) and 74% (with precipitation) of 222Rn activity concentration. The observations show that most of the time both detector types follow the same pattern. Still, there is no single disequilibrium factor that could be used to exactly transform short-lived progeny to 222Rn activity concentration under all meteorological conditions.