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How reliable are process-based 222radon emission maps? Results from an atmospheric 222radon inversion in Europe

Maier, Fabian ; Falge, Eva ; Gachkivskyi, Maksym ; Henne, Stephan ; Karstens, Ute LU orcid ; Kikaj, Dafina ; Levin, Ingeborg ; Manning, Alistair ; Rödenbeck, Christian and Gerbig, Christoph (2025) In Atmospheric Chemistry and Physics 25(19). p.12779-12809
Abstract

The radioactive noble gas radon (222Rn) is a suitable tracer for atmospheric transport and mixing processes that can be used to evaluate and calibrate atmospheric transport models or to estimate greenhouse gas (GHG) emissions using the so-called radon tracer method (RTM). However, these applications require reliable estimates of the 222Rn fluxes from the soil. This study evaluates two process-based 222Rn flux maps in central Europe in 2021 using the flux results from a 1-year 222Rn inversion. The maps are based on different soil moisture reanalysis products (GLDAS-Noah and ERA5-Land), which are used to describe the diffusive 222Rn transport in the soil. The 222Rn... (More)

The radioactive noble gas radon (222Rn) is a suitable tracer for atmospheric transport and mixing processes that can be used to evaluate and calibrate atmospheric transport models or to estimate greenhouse gas (GHG) emissions using the so-called radon tracer method (RTM). However, these applications require reliable estimates of the 222Rn fluxes from the soil. This study evaluates two process-based 222Rn flux maps in central Europe in 2021 using the flux results from a 1-year 222Rn inversion. The maps are based on different soil moisture reanalysis products (GLDAS-Noah and ERA5-Land), which are used to describe the diffusive 222Rn transport in the soil. The 222Rn inversion was conducted using the CarboScope-Regional inversion system and observational data from 17 atmospheric sites in central Europe in 2021. We observe that, in particular, the ERA5-Land-based 222Rn flux map underestimates the data-driven fluxes from the inversion. Our inversion yields ca. 20 % (GLDAS-Noah) to almost 100 % (ERA5-Land) larger 222Rn fluxes than the respective process-based prior fluxes within a domain covering Germany. Also, the temporal variability seems to be underestimated by the process-based flux maps. Using a flat (uniform) prior inversion, we found a significant anti-correlation of −0.6 (and −0.8) between the posterior 222Rn flux and the GLDAS-Noah (and ERA5-Land) soil moisture time series, indicating that soil moisture is an important driver for the temporal variability in the 222Rn fluxes. To investigate the robustness of our flux estimates, we run the inversion with three different transport models (STILT, FLEXPART, NAME). The respective annual mean flux results agree within ca. 10 %.

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author
; ; ; ; ; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
radon emissions, inverse modeling
in
Atmospheric Chemistry and Physics
volume
25
issue
19
pages
31 pages
publisher
Copernicus GmbH
external identifiers
  • scopus:105019964489
ISSN
1680-7316
DOI
10.5194/acp-25-12779-2025
language
English
LU publication?
yes
additional info
Publisher Copyright: © Author(s) 2025.
id
ea2d79e1-a036-4087-8aee-735d3694376d
date added to LUP
2025-12-02 12:05:03
date last changed
2025-12-02 12:32:12
@article{ea2d79e1-a036-4087-8aee-735d3694376d,
  abstract     = {{<p>The radioactive noble gas radon (<sup>222</sup>Rn) is a suitable tracer for atmospheric transport and mixing processes that can be used to evaluate and calibrate atmospheric transport models or to estimate greenhouse gas (GHG) emissions using the so-called radon tracer method (RTM). However, these applications require reliable estimates of the <sup>222</sup>Rn fluxes from the soil. This study evaluates two process-based <sup>222</sup>Rn flux maps in central Europe in 2021 using the flux results from a 1-year <sup>222</sup>Rn inversion. The maps are based on different soil moisture reanalysis products (GLDAS-Noah and ERA5-Land), which are used to describe the diffusive <sup>222</sup>Rn transport in the soil. The <sup>222</sup>Rn inversion was conducted using the CarboScope-Regional inversion system and observational data from 17 atmospheric sites in central Europe in 2021. We observe that, in particular, the ERA5-Land-based <sup>222</sup>Rn flux map underestimates the data-driven fluxes from the inversion. Our inversion yields ca. 20 % (GLDAS-Noah) to almost 100 % (ERA5-Land) larger <sup>222</sup>Rn fluxes than the respective process-based prior fluxes within a domain covering Germany. Also, the temporal variability seems to be underestimated by the process-based flux maps. Using a flat (uniform) prior inversion, we found a significant anti-correlation of −0.6 (and −0.8) between the posterior <sup>222</sup>Rn flux and the GLDAS-Noah (and ERA5-Land) soil moisture time series, indicating that soil moisture is an important driver for the temporal variability in the <sup>222</sup>Rn fluxes. To investigate the robustness of our flux estimates, we run the inversion with three different transport models (STILT, FLEXPART, NAME). The respective annual mean flux results agree within ca. 10 %.</p>}},
  author       = {{Maier, Fabian and Falge, Eva and Gachkivskyi, Maksym and Henne, Stephan and Karstens, Ute and Kikaj, Dafina and Levin, Ingeborg and Manning, Alistair and Rödenbeck, Christian and Gerbig, Christoph}},
  issn         = {{1680-7316}},
  keywords     = {{radon emissions; inverse modeling}},
  language     = {{eng}},
  month        = {{10}},
  number       = {{19}},
  pages        = {{12779--12809}},
  publisher    = {{Copernicus GmbH}},
  series       = {{Atmospheric Chemistry and Physics}},
  title        = {{How reliable are process-based <sup>222</sup>radon emission maps? Results from an atmospheric <sup>222</sup>radon inversion in Europe}},
  url          = {{http://dx.doi.org/10.5194/acp-25-12779-2025}},
  doi          = {{10.5194/acp-25-12779-2025}},
  volume       = {{25}},
  year         = {{2025}},
}