Abstract
Abstract. Although atmospheric 222radon (222Rn) activity concentration measurements are currently performed worldwide, they are being made by many different laboratories and with fundamentally different measurement principles, so compatibility issues can limit their utility for regional-to-global applications. Consequently, we conducted a European-wide 222Rn ∕ 222Rn progeny comparison study in order to evaluate the different measurement systems in use, determine potential systematic biases between them, and estimate correction factors that could be applied to harmonize data for their use as a tracer in atmospheric applications. Two compact portable Heidelberg radon monitors (HRM) were moved around to run for at least 1 month at each of the nine European measurement stations included in this comparison. Linear regressions between parallel data sets were calculated, yielding correction factors relative to the HRM ranging from 0.68 to 1.45. A calibration bias between ANSTO (Australian Nuclear Science and Technology Organisation) two-filter radon monitors and the HRM of ANSTO ∕ HRM = 1.11 ± 0.05 was found. Moreover, for the continental stations using one-filter systems that derive atmospheric 222Rn activity concentrations from measured atmospheric progeny activity concentrations, preliminary 214Po ∕ 222Rn disequilibrium values were also estimated. Mean station-specific disequilibrium values between 0.8 at mountain sites (e.g. Schauinsland) and 0.9 at non-mountain sites for sampling heights around 20 to 30 m above ground level were determined. The respective corrections for calibration biases and disequilibrium derived in this study need to be applied to obtain a compatible European atmospheric 222Rn data set for use in quantitative applications, such as regional model intercomparison and validation or trace gas flux estimates with the radon tracer method.
Highlights
222Radon (222Rn) is a short-lived radioactive noble gas, which is produced in all soils from the radioactive decay of 226radium (226Ra), a member of the primordial 238uranium decay series. 222Rn is the first gaseous constituent in this series and has a chance of escaping from the soil zone into the atmosphere by diffusion
From 10 July to 26 August 2012 a Heidelberg radon monitors (HRM) was installed on the Cabauw tower at 180 m, so that measurements could be conducted in parallel to the ANSTO system without additional tubing
Data from a few hours have been flagged as obvious outliers, but the remaining measurements yielded a slope of ANSTO / HRM = 1.30 ± 0.01 (Fig. S2, lower panel), i.e. on average the ANSTO monitor measured almost 30 % higher 222Rn activity concentrations at the 20 m level than 214Po activities measured with the HRM
Summary
The exhalation rate of 222Rn from continental surfaces depends on the soil properties, mainly 226Ra content, grain size distribution, porosity, and moisture content. The 222Rn flux from (ocean) water surfaces is negligible (Schery and Huang, 2004) compared to that from continental soils; the atmospheric 222Rn activity concentration can serve as a (qualitative) tracer to distinguish continental from marine air masses If the continental 222Rn exhalation rate and its spatial and temporal distribution are known, 222Rn can serve as a quantitative tracer for atmospheric boundary layer mixing and transport model validation If the continental 222Rn exhalation rate and its spatial and temporal distribution are known, 222Rn can serve as a quantitative tracer for atmospheric boundary layer mixing and transport model validation (e.g. Jacob and Prather, 1990; Jacob et al, 1997; Taguchi et al, 2011; Williams et al, 2011)
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