the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Apr 2025
The flask monitoring program for high-precision atmospheric measurements of greenhouse gases, stable isotopes, and radiocarbon in the central Amazon region
Abstract. Long-term and high-precision measurements of the mole fraction of greenhouse gases (GHG), together with their isotopic composition, are of fundamental importance to understand land-atmosphere interactions. Current flask monitoring programs have important information gaps in large regions of the Earth, particularly in the southern hemisphere and in continental tropical regions. Here, we report on the initiation of a monitoring program and the resulting dataset of high-precision GHG measurements at the Amazon Tall Tower Observatory (ATTO), located in the central Amazon region of Brazil. In September 2021, we installed an automated flask sampler designed and built by the Integrated Carbon Observation System (ICOS) to collect air samples in 3-liter flasks at a height of 324 m above ground level. Samples are collected weekly, during a one-hour integration time between 13:00 and 14:00 h local time (17:00–18:00 UTC). The flasks are shipped to Jena, Germany, for analyses of CO2, CO, CH4, N2O, H2, SF6, 13C–CO2, 14C–CO2, 18O–CO2, 13C–CH4, 2H–CH4, O2/N2, and Ar/N2 at the laboratories of the Max Planck Institute for Biogeochemistry (MPI-BGC). Measurements from this monitoring program provide reference information for this site and act as an additional independent quality control for other measurements in the region. The record of SF6 and simulations based on a regional atmospheric transport model suggest that the footprint of the measurements is predominantly from the southeasterly and northeasterly directions. The time series of the different gas species measured in this monitoring program are being made publicly available through the ATTO data portal and the atmospheric flask sampling program of the MPI-BGC.
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Status: final response (author comments only)
- RC1: 'Comment on essd-2025-151', Anonymous Referee #1, 05 May 2025
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RC2: 'Comment on essd-2025-151', Anonymous Referee #2, 27 Jun 2025
The paper describes a very impressive and unique data set. The data is obviously of excellent quality, and a lot of care and work has gone into it. Being very familiar with the challenges of flask sampling and the logistics involved, I know that this is a truly unique effort. I specifically admire that the measurements are made on a continuous and long-term basis. The paper itself is written in simple, clear English that I found easy to read and understand. I would have only a few minor stylistic comments and suggestions if it were not for the data filter used to determine “unreliable data points.” I chose major revisions, simply because I think this point needs to be reviewed again.
From the last paragraph, I get the impression that maybe the authors are more used to so-called background sites. The filtering method used might potentially be appropriate at a site where minimal variability is expected and where high-frequency observations are available. Even then, I would probably rename the flag to a pollution flag or non-baseline flag. At a site with more complex atmospheric influence such as this one, statistically filtering the data may remove realistic and normal variability. In weekly flask data, there is not necessarily a lot of connection between each individual observation point; sources/sinks and meteorological conditions may change at a higher frequency than that.
In Figure 4, I find the variability of CO₂ (only one flagged point) and H₂ (lots of flagged points) to be fully within normal atmospheric values. I assume the statistical filter is used to determine spurious values that cannot be explained, such as the SF₆ value and the N₂O value that are clearly below southern hemispheric background values (I compare my low data points to a southern hemisphere background site such as Cape Grim to determine what is realistic and what is not). I agree that those points should be flagged, as they are clearly not realistic. Those low values are probably caused by a problem during the sampling and some of the fill gas from the ICOS flask lab remaining in the flask, diluting the sample. I believe NOAA specifically uses a fill gas that is unlike atmospheric values to diagnose incomplete filling through these unrealistically low values.
In my opinion, this point should then be flagged in all compounds, as an incomplete filling affects all data, not just the obviously strange-looking one. For the ¹³C-CH₄, Figure 5 shows a very enriched value around -37 ‰, that I think may be unrealistic, I tried to look up its matching CH₄ data point but I was unable to find that -37 ‰ point in the repository, I attached the plot I get. The ¹⁴C-CO₂ seems realistic to me. As the authors correctly identified, there are some depleted points consistent with fossil fuel burning and some enriched values that are probably caused by biomass burning. Enriched values can also be from nuclear industry emissions, but I presume biomass burning is more likely here.
I do not understand the atmospheric variability of the O₂/N₂, Ar/N₂, ¹⁸O-CO₂, and δ²H-CH₄ values well enough to comment on those.
I believe strongly that only data points with clear instrumental problems or points that are evidently unrealistic should be flagged. Modelers using the data set should be aware of the variability of the atmosphere and use their own judgment on how much weight an individual sampling point should be given. Just flagging that one flask with the low N₂O and SF₆ value and re plotting all the data without filtering would satisfy me as a revision.The hard work and passion that went in to this data set is evident and besides the filtering I have only very minor comments.
• Line 28: Mentions these aircraft campaigns, but it is not evident in the text that the previously referenced papers are aircraft campaigns.
• Line 52: “Infrastructure to access relevant heights” — Could you please reword this to make clear what you mean? At the moment, the ICOS sampler description and the rarity of having remote infrastructure with tall towers that provide appropriate sampling heights are a bit convoluted.
• Line 96: “Each flask has one valve at each end” — maybe: Each flask is equipped with a valve at both ends.
• Figure 2: There is a car icon missing between the Isolab and the ¹⁴C lab. I think the text description in Chapter 2.3.1 is important to show how remote the site is, but it could maybe be summarized a bit more, especially for the transport back to Jena. At the moment, we have the chapter description, the graph, and the description of the graph. Maybe the description of the graph could be more along the lines of a title such as: Flow chart of shipping logistics, or the return shipment could be summarized as being the same process in reverse order?
• There is a bit of repetition in the description of the assignment of the unique sample number and the analysis in Jena as well — Line 120 and 124.
• Line 139–140: Could you check the references? They do not seem to contain a detailed description of the measurement setup, or alternatively, give more details about the setup in the description.
• Line 149: “Measurement uncertainties are propagated to include both individual measurement and scaling uncertainties” — I think scaling probably refers to the calibration scale? So maybe something along the lines of:
• The uncertainties reported contain the individual measurement uncertainty as well as the propagated calibration scale uncertainty.
• Or: Error propagation was used to account for the measurement uncertainty as well as the propagated calibration scale error.
• Line 162–163: Could you describe or reference the quality control process used?
• Line 173–174: “For the ATTO flask program, we combine all data on mole fractions and isotopes with data on atmospheric radiocarbon, and release an expanded report that includes all gas species measured at the site.” — Please rephrase. Maybe something along the lines of:
• All measurement results from the different instruments and labs are combined into one report.
• Line 235–236: The formatting is a bit awkward, as there are just two text lines on the page with Figure 5.Citation: https://doi.org/10.5194/essd-2025-151-RC2 -
EC1: 'Comment on essd-2025-151', Tobias Gerken, 27 Jun 2025
I would like to thank the reviewers for their efforts and constructive comments. I am recommending for the authors to carefully consider the review comments, especially with respect to the clarity in presentation of results and figure quality.
Thank you so much!
Tobias Gerken
Citation: https://doi.org/10.5194/essd-2025-151-EC1
Data sets
High-precision atmospheric measurements of greenhouse gases, stable isotopes, and radiocarbon in carbon dioxide in flask samples collected at the ATTO Tall Tower. Version 2025.1 C. A. Sierra et al. https://doi.org/10.17871/ATTO.465.13.1902
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