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

Parallel monitoring of 222Rn and its short-livedprogeny (218Po and 214Pb) were carried out from Novem-ber 2007 to April 2008 close to the top of the Schauinslandmountain,  partly covered with forest,  in South-West Ger-many. Samples were aspired from the same location at 2.5 mabove ground level.  We measured 222Rn with a dual flowloop, two-filter detector and its short-lived progeny with aone-filter detector.   A reference sector for events, facing asteep valley and dominated by pasture, was used to minimizedifferences between 222Rn and progeny-derived 222Rn activ-ity concentrations.  In the two major wind sectors coveredby forest to a distance between 60 m and 80 m towards thestation progeny-derived 222Rn activity concentration was onaverage equal to 87% (without precipitation) and 74% (withprecipitation) of 222Rn activity concentration.   The obser-vations show that most of the time both detector types fol-low the same pattern. Still, there is no single disequilibriumfactor  that  could  be  used  to  exactly  transform  short-livedprogeny to 222Rn activity concentration under all meteoro-logical conditions.