An international intercomparison of marine atmospheric radon 222 measurements in Bermuda

Abstract

As part of an international measurement intercomparison of instruments used to measure atmospheric 222Rn, four participating laboratories made nearly simultaneous measurements of 222Rn activity concentration in commonly sampled, ambient air over approximately a two-week period, and three of these four laboratories participated in the measurement comparison of 14 introduced samples with known, but undisclosed ("blind') 222Rn activity concentration that could be related to US national standards. The standardized sample additions were obtained with a calibrated 226Ra source and a specially designed manifold used to obtain well-known dilution factors from simultaneous flow rate measurements. Sample additions covered a range from aproximately 2.5 to 35 Bq m-3. The overall uncertainty in the later concentrations was in the general range of 10% at a 3 standard deviation uncertainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the standard additions and almost within expected statistical variations. These same two laboratories, however, at lower ambient concentrations, exhibited a systematic difference with an average offset of roughly 0.3 Bq m-3. The third laboratory participating in the measurement of standardized sample additions was systematically low by about 65-70%, which was also confirmed in their ambient air concentration measurements. The fourth laboratory, participating in only the ambient measurement part of the intercomparison, was also systematically low by at least 40% with respect to the first two aforementioned laboratories. -from Authors