An international marine-atmospheric Rn-222 measurement intercomparison in Bermuda .2. Results for the participating laboratories

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 2 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. The exercise was conducted in Bermuda in October 1991. The 222Rn activity concentrations in ambient Bermudian air over the course of the intercomparison ranged from a few hundredths of a Bq · m−3 to about 2 Bq · m−3, while the standardized sample additions covered a range from approximately 2.5 Bq · m−3 to 35 Bq · m−3. The overall uncertainty in the latter concentrations was in the general range of 10 %, approximating 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 averaged 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 % to 70 %, with respect to the standard addition 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 laboratories.

Characterizing Atmospheric Transport Pathways to Antarctica and the Remote Southern Ocean Using Radon-222

“…The measurement techniques compared included intermittent and continuous two-filter detectors, cryogenic separation using charcoal, and intermittent Radon-222 progeny collection on filters with equilibrium ratio assumptions. As noted by Collé et al (1996b), both twofilter techniques "were in excellent agreement with the NIST [ 222 Rn] additions." In general, however, the continuous two-filter observations were overly smoothed by the detector's 90-min time constant, changing particulate concentrations within the detector added considerably to the detector's counting uncertainty, concentrations were initially overestimated by ∼10% (reduced to an overestimation of 2.7% only after a retrospective instrumental background correction), and there was considerable variability in concentrations at very low ambient radon levels, thought to be attributable to problems with instrumental background characterization.…”

“…The dual-flow-loop two-filter radon detectors employed in this study are based on the one originally tested in the Collé et al (1996b) study, however, there have been considerable improvements to their design and performance in the 26 years since the Collé et al (1996b) inter-comparison campaign. The original ANSTO two-filter radon detector design was superseded in the late 1990s by a completely new design involving the introduction of an innovation known as a "dual flow-loop" (Whittlestone and Zahorowski, 1998).…”

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

“…This is very close to the disequilibrium factor (0.85) estimated for this station by Schmidt (1999, as cited in Schmidt et al, 2003. Much larger differences between detectors have been reported (Collé et al, 1996). Because of physical plausibility we assume in our further analysis that the observed off-set is entirely due to internal instrumental effects and not explained by environmental factors.…”

“…Our objective was to investigate what difference changing meteorological conditions may cause between 222 Rn measurements with one-and two-filter detectors. After the inter-comparison of four different detectors, Collé et al (1996) …”

“…Other instruments include those based on the design by Iida et al (1996) and widely used in East Asia (e.g. Moriizumi et al, 2008), and the two filter detector developed by the Environmental Measurements Laboratory (EML) as described in Collé et al (1996). Hence, the instruments in our study represent the two measurement principles of a majority of detectors currently in use.…”