Predicting terrestrial <sup>222</sup>Rn flux using gamma dose rate as a proxy

Abstract

Abstract. 222 Rn is commonly used as a natural tracer for validating climate models. To improve such models a better source term for 222 Rn than currently used is necessary. The aim of this work is to establish a method for mapping this source term by using a commonly measured proxy, the gamma dose rate (GDR). Automatic monitoring of GDR has been networked in 25 European countries by the Institute for Environment and Sustainability at the Joint Research Centre (JRC IES) in Ispra, Italy, using a common data format. We carried out simultaneous measurements of 222 Rn flux and GDR at 63 locations in Switzerland, Germany, Finland and Hungary in order to cover a wide range of GDR. Spatial variations in GDR resulted from different radionuclide concentrations in soil forming minerals. A relatively stable fraction (20%) of the total terrestrial GDR originates from the 238 U decay series, of which 222 Rn is a member. Accordingly, spatial variation in terrestrial GDR was found to describe almost 60% of the spatial variation in 222 Rn flux. Furthermore, temporal variation in GDR and 222 Rn was found to be correlated. Increasing soil moisture reduces gas diffusivity and the rate of 222 Rn flux but it also decreases GDR through increased shielding of photons. Prediction of 222 Rn flux through GDR for individual measurement points is imprecise but un-biased. Verification of larger scale prediction showed that estimates of mean 222 Rn fluxes were not significantly different from the measured mean values.

Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch

“…It is emitted by all soils at a relatively constant rate (Szegvary et al, 2007;Zhang et al, 2011). Its only significant sink is radioactive decay.…”

Inferring <sup>222</sup>Rn soil fluxes from ambient <sup>222</sup>Rn activity and eddy covariance measurements of CO<sub>2</sub>

“…Recently, several approaches have been applied to quantify 222 Rn surface fluxes: (1) using gamma dose radiation as a proxy for 222 Rn (Szegvary et al, 2007;Manohar et al, 2016) and (2) modelling the production and transport of 222 Rn in soils (Hirao et al, 2010;Karstens et al, 2015a). These efforts have provided new tools for studying the driving mechanisms behind the 222 Rn soil flux on relatively large spatial scales.…”

“…Liu et al, 1984;Chevillard et al, 2002) and to evaluate or compare the transport component in atmospheric trans-port models (Dentener et al, 1999;Gupta et al, 2004;Zahorowski et al, 2004). Another highly useful application of 222 Rn is the direct inversion method commonly referred to as the 222 Rn tracer method (Levin, 1987;Schmidt et al, 1996;van der Laan et al, 2014). With this method, the ratio of the 222 Rn surface flux to a measured 222 Rn activity concentration difference over time at a certain observation height can be applied to calculate the surface flux of another constituent (e.g.…”

Variability and budget of CO<sub>2</sub> in Europe: analysis of the CAATER airborne campaigns – Part 2: Comparison of CO<sub>2</sub> vertical variability and fluxes between observations and a modeling framework

“…In reality this flux depends on soil bedrock type, total pore space, tortuosity, soil moisture and precipitation. Its mean variability in Western Europe soils is of the order of 30% (Nazaroff, 1992;Jutzi, 2001;Ielsch et al, 2002;Szegvary et al, 2007). Secondly, the 222 Rn measurement precision itself is ∼30% which translates into a relative error of the same magnitude in the inferred CO 2 surface flux.…”