the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Nov 2024
Six years of greenhouse gas fluxes at Saclay, France, estimated with the Radon Tracer Method
Abstract. Here, we use carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), nitrous oxide (N2O) and radon (222Rn) data from the Saclay ICOS tall tower in France to estimate CO2, CH4 and CO fluxes within the station footprint from January 2017 to December 2022 and N2O fluxes from February 2019 to December 2022 using the Radon Tracer Method (RTM).
We first performed a sensitivity study of this method applied to CH4 and combined with different radon exhalation maps including the improved European process-based radon flux maps developed within 19ENV01 traceRadon and back-trajectories in order to optimize it. Then, radon exhalation maps from the 19ENV01 traceRadon project, STILT trajectories from the ICOS Carbon Portal, best estimate of radon activity concentration and greenhouse gas data have been used to estimate the surface emissions. To our knowledge, this is the first study using the latest radon exhalation maps and standardized radon measurements to estimate CO2, CH4, CO and N2O surface emissions. We found that the average RTM estimates are 609 ± 402 mg m−2 h−1, 0.81 ± 0.66 mg m−2 h−1, 1.04±1.80 mg m−2 h−1 and 0.063 ± 0.079 mg m−2 h−1 for CO2, CH4, CO and N2O respectively. These fluxes are in good agreement with the literature.
CH4, N2O and CO are in fair agreement with the inventories, though with higher values. CO2 fluxes are about five times higher than modeled anthropogenic and biogenic fluxes combined. The differences mainly occur during summer, and the CO/CO2 ratio points toward a misrepresentation of the biogenic fluxes at this time by the WRF-VPRM version used here.
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RC1: 'Comment on egusphere-2024-3107', Anonymous Referee #1, 28 Jan 2025
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This paper used the Radon Tracer Method (RTM) to estimate greenhouse gas (CO2, CH4, N2O) and CO fluxes at Saclay, France during the period of January 2017 – December 2022. The authors examined the sensitivity of the method to the use of different Radon exhalation maps. Radon exhalation maps from the 19ENV01 traceRadon project, STILT back trajectories from the ICOS Carbon Portal, estimates of radon activities and greenhouse gas data were then used to estimate surface emissions. They found that the estimated CO2, CH4, CO and N2O surface emissions were in good agreement with the literature and that CH4, N2O and CO fluxes were also in fair agreement with inventories. The observation-based RTM method provides an independent approach (alternative to inverse modeling) to verify greenhouse gas fluxes, as demonstrated in this study. This reviewer’s major concern is that the presentation of this paper needs improvement and in some places the texts are hard to understand (see examples below). Publication on ACP is recommended after serious editing and addressing the comments below.
Abstract, Line 12: “CH4, N2O and CO are also in fair agreement with the inventories, though with higher values” – do you actually mean “CH4, N2O and CO fluxes”? “To our knowledge, this is the first study using the latest radon exhalation maps and standardized radon measurements to estimate CO2, CH4, CO and N2O surface emissions” - Is this for any site or for Saclay only? “These fluxes are in good agreement with the literature” – Could you cite the values from the literature for each species?
Page 3, Line 5: GHG and 222Rn “concentrations”?
Page 3, Line 8: Kikaj et al. (2024) – when was this submitted? Not available to the reviewer.
Page 3, Line 10: “the radon flux was considered homogeneous over time and space” – is this said for Paris or Europe? Probably this was an assumption made in the study of Yver et al. (2009)? “as it is now known that the radon fluxes varies on space and time” – it is long known (way before 2009) that the radon fluxes vary on space and time.
Page 4, Line 4: “the nocturnal PBL was above 100m….” – I think you meant the nocturnal PBL height was above the 100 m sampling height of SAC tower.
Page 4, Line 27: “respectively, “ – add “,” before respectively (also check elsewhere in the text).
Figure 1 caption: what is the CCGCRV code?
Section 2.2: Please add references for the Radon Tracer Method at the beginning of this section since this method has previously been used.
Page 5, Line 11: Under which conditions will this (<<) be valid?
Page 8, Line 30: Please add “N” for latitude and “W” for longitude.
Page 9, Line 19: obtained BY
Page 10, Line 7: are showN.
Page 10, Lines 9-11: It’s well known that radon emissions under freezing temperatures in winter are much reduced. Is the higher soil humidity, which prevents the radon from exhaling, due to low temperature in winter?
Page 10, Line 15: remove the redundant “Bq”.
Figure 3: “the fixed flux from the literature” --- which literature?
Figure 4 caption: using either….or both the maps and the footprints.
Figure 5 caption: it’s not clear whether “fluxes” are for Rn or CH4. Please clarify to avoid confusion.
Figure 6: “CH4 2 Flux”?
Figure 8 caption: “On the left panels, …shown, in the middle panel, we show…” - Editing is needed.
Figure 9: what is “por”?
Figure 18, Line 32: FEWER events
Page 20, Line 6: “for the others, it was either the radon increase that was too low or the number of available hours” – Please clarify.
Page 21, Line 6: “an underestimation for the higher ones” – Not clear. RTM overestimates?
Page 21, Line 15: “though soil chambers” – do you mean “through soil chambers”?
Page 21, Line 22: “CO RTM and TNOf fluxes do not show a clear seasonal cycle or a trend over the period” – could you make a seasonality plot?
Page 24, Line 1: “No trend is observed” – this is also mentioned elsewhere. Did you try to do regression analysis?
Page 24, Line 2-3: “we are looking here at nocturnal fluxes without photosynthesis only respiration” – how about “…without photosynthesis (i.e., with respiration only)”?
Page 24, Line 5, Line 14: “in average” should be “on average”; change “like” to “as”.
Page 26, Line 3: do you mean “CH4, N2O and CO fluxes are in fair agreement with the inventories”?
Code and data availability: the ICOS Carbon Portal address is not provided. Both the FLEXPART trajectories and the RTM code are not provided (shared on demand only) but should be archived in a public depository (e.g., https://zenodo.org/).
Citation: https://doi.org/10.5194/egusphere-2024-3107-RC1
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