Atmospheric Chemistry and Physics Discussions
www.atmos-chem-phys-discuss.net
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2007
10.5194/acpd-7-1877-2007
http://www.atmos-chem-phys-discuss.net/7/1877/2007/
http://www.atmos-chem-phys-discuss.net/7/1877/2007/acpd-7-1877-2007.html
http://www.atmos-chem-phys-discuss.net/7/1877/2007/acpd-7-1877-2007.pdf
1877
1892
2007-02-05
Predicting terrestrial <sup>222</sup>Rn flux using gamma dose rate as a proxy
T. Szegvary
t.szegvary@unibas.ch
M. C. Leuenberger
F. Conen
Environmental Geosciences, Department of Geosciences, University of Basel, Switzerland
Climate and Environmental Physics, Physics Institute, University of Bern, Switzerland
<sup>222</sup>Rn is commonly used as a natural tracer for validating climate
models. To improve such models a better source term for <sup>222</sup>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 <sup>222</sup>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
<sup>238</sup>U decay series, of which <sup>222</sup>Rn is a member. Accordingly,
spatial variation in terrestrial GDR was found to describe almost 60% of
the spatial variation in <sup>222</sup>Rn flux. Furthermore, temporal variation in
GDR and <sup>222</sup>Rn was found to be correlated. Increasing soil moisture
reduces gas diffusivity and the rate of <sup>222</sup>Rn flux but it also
decreases GDR through increased shielding of photons. Prediction of
<sup>222</sup>Rn flux through GDR for individual measurement points is imprecise
but un-biased. Verification of larger scale prediction showed that estimates
of mean <sup>222</sup>Rn fluxes were not significantly different from the measured
mean values.
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