Intercomparison of methods for investigating the physical characteristics of radon decay products in the indoor environment

The average activity concentrations of radon gas and its short-lived decay products were measured under normal living conditions and deviated by less than 10 % during an intercomparison between the three European groups of the National Radiological Protection Board (UK), Ghent (Belgium) and Göttingen (Germany). The spread in the derived unattached fraction, f_p, ranged up to 50 % in situations without additional aerosol sources (average f_p =0.1) and the variation in the evaluated attachment rate X and plateout rates q^a and q^f1 was sometimes two-fold. Different size fractionating methodologies yield similar AMD/AMADs of 200 nm for the accumulation mode (deviation <30 %) during measurements in a low ventilated room with an aged aerosol. Active aerosol sources yield complex size distributions in the attached region and varied by a factor of 2.