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

Abstract. 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.