First deployment of active AirCore in a volcanic plume at Mount Etna

Degen, Johannes; Bobrowski, Nicole; Bossard, Mélisende M.; Boucher, Lucie; Chen, Huilin; Engel, Andreas; Geil, Bastien H.; Giuffrida, Giovanni B.; van Heuven, Steven; Hoffmann, Thorsten; Karbach, Niklas; Ortenzi, Gianluigi; Schuck, Tanja J.

doi:10.5194/egusphere-2026-1865

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https://doi.org/10.5194/egusphere-2026-1865

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21 May 2026

| 21 May 2026

Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

First deployment of active AirCore in a volcanic plume at Mount Etna

Johannes Degen, Nicole Bobrowski, Mélisende M. Bossard, Lucie Boucher, Huilin Chen, Andreas Engel, Bastien H. Geil, Giovanni B. Giuffrida, Steven van Heuven, Thorsten Hoffmann, Niklas Karbach, Gianluigi Ortenzi, and Tanja J. Schuck

Abstract. Uncrewed Aerial Systems (UAS) are by now well established platforms for observations in volcanic plumes which are a challenging environment. Options for trace gas observations inside volcanic plumes still remain limited because sophisticated measurement techniques for high-precision observations of trace gases often require instrumentation that cannot be used on board UAS due to high weight and power consumption. UAS-borne sampling of air followed by post-flight analysis can extend the number of observable trace gases as well as the measurement quality. Originally developed for stratospheric observations, AirCore sampling with long coiled tubes has proven to be a light-weight sampling technique to probe parts of the atmosphere that are otherwise difficult to access. Trace gas analysis of sampled air is done post-flight, most commonly with fast high-precision optical methods with continuous flow analysers, delivering high-quality and high-resolution trace gas mole fractions. While balloon-borne AirCore setups perform passive sampling making use of natural pressure differences, we used a UAS-deployable small active AirCore setup collecting air with a pump. In July 2024, this setup was deployed on a UAS alongside electrochemical and optical gas sensors to probe the volcanic plumes of Mount Etna (Sicily, Italy), which was particularly active at the time. This was to our knowledge the first time that the AirCore sampling technique was used inside volcanic plumes. The air sample was successfully analysed with cavity-ring down spectroscopy for carbon monoxide (CO), carbon dioxide (CO₂) and methane (CH₄). While CO₂ and often also CO mole fractions were markedly enhanced in the plume, no significant change of CH₄ was observed. The ratio of CO and CO₂ mole fraction enhancements was found to be rather low which might point at fast oxidation processes.

Received: 30 Apr 2026 – Discussion started: 21 May 2026

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Measurement Techniques.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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RC1:
'Comment on egusphere-2026-1865', Anonymous Referee #1, 08 Sep 2026 reply
First deployment of active AirCore in a volcanic plume at Mount Etna
Major Comments
This study provides an application of Aircore instrument installed on a UAV platform to observe volcanic plumes at Mount Etna. It includes several UAV flights around two different craters and measures atmospheric trace gas mixing ratios using Aircore and a low-cost sensor platform. I value the effort went into collecting this data and putting together this instrumentation and UAV platform. However, my main concern about this study is the way authors state their novelty. As AMT aims to publish studies that advances measuring techniques and not the application of an existing methodologies, I found the emphasized novelty of the study not suited for a publication in AMT. UAV-based Aircore measurements is being conducted for almost a decade now and applying the same technique over the volcanic plume in my opinion would not be considered as novel. There is an improvement in measurement retrieval from the Aircore that accounts for pressure changes, however I don’t think this improvement alone is enough for acceptance in AMT and the way it was presented seems overshadowed by the application. I think authors should change their narrative and concentrate a bit more, for example comparing the performance of Aircore and low-cost sensor (after the correction) which I think would be much more valuable than only reporting Aircore measurements. Connected to that, I think the title needs to be revised. Another point is the manuscript lack in-depth analysis of the flights, in some flights the main wind direction and observed plume do not even match but this was not even mentioned in the manuscript. I think the manuscript has the potential to be of interest to the community but needs to go through a major revision and the novelty needs to be emphasized in a way that is more suited to be published in AMT. Below I have list of comments which I hope will help the authors to improve their manuscript.

Specific Comments
Lines 3-4, I think this statement undermines the efforts of several studies showing in-situ high precision trace gas measurements using UAV platforms. Please see the comment number 3.

Lines 12-13, I do not see this application as an aspect of novelty and think emphasizing in abstract would not be fitting.

Lines 61 – 64, I think this information is a bit misleading. There exist several studies showing in-situ high precision gas concentration measurements using UAVs, some examples are Kunz et al. 2018, Bonne et al. (2024), Bolek et al. (2024, 2026), Beattie et al. (2026), Dooley et al (2025), van Hove et al. (2026). Although these references are not specifically from volcanoes, they measure CO₂ and CH₄ mixing ratios which were also measured in this study (please don't feel obliged to cite these studies, it is only provided as reference for the statement).

Line 133, is this a different CO₂ sensor than MGA? Also showing MGA placement in schematic would be very helpful in Figure 2.

Line 144, I would suggest not to use “good” or “high” precision to describe a commercial analyzer specification, simply stating the numbers would be sufficient.

Line 145, what is the temporal resolution for these precisions?

Line 150 – 156, Could authors provide any quantitative measure about the impacts of delay time on the mixing/diffusion of air samples and on the spatial information? This may not be easy to provide without a dedicated experiment but at least some crude numbers or back of the envelope calculations would help the readers.

Line 250, Figure S3, The wide range of spatial resolution given in figure do not help much. I would suggest authors to first do some filtering, for example omitting the travel between the landing and take-off position to area of interest. I assume than this graph will become more interpretable and inform us about spatial resolution of the collected data.

Section 2.4, it seems that this is the only improvement made to Aircore measurements, it would be useful to emphasize this section a bit more so that the novelty becomes clearer.

Table 3, are these max flight speeds correct? According to technical specs DJI matrice 350 has max horizontal speed of 23 m/s and vertical is 7 m/s. Maybe double check these values or explain how these flight speeds were reached?

Lines 279 – 280, Could you please provide some more information on how this communication between sensor package and tablet computer was established? Considering the distance of over a km, some details may help researchers in this field.

Lines 320 – 326, This comparison is ill suited in my opinion and the issue in NDIR instrument is not clearly provided, is it offset or drift? If this ‘offset’ can be corrected why this correction is not applied to the instrument? I think a fair comparison would be more suitable to not misrepresent the sensor package performance and misinform the reader about low-cost instruments.

Lines 327 – 330, Can you provide some quantitative measure in here? Maybe conducting some spectral analysis or providing how correlated these two signals are? As there seems to be a temporal shift between the signals.

Lines 331 – 333, This sentence sounds a bit off please clarify.

Lines 335 – 336, It may be better to provide the enhancements over background rather than measured concentrations in here, so that the observed peaks can be easily interpreted by both analyzers?

Lines 339 – 340, As I pointed it out earlier, if these part of the measurements (flying back and forth to launch position) are not interesting within the context of the study they may simply be omitted and more focus can be given to the plume encounters.

Lines 348 – 350, Indeed it is time interval between sampling points, however spatial resolution is directly depending on the UAVs flight speed regardless direction and pattern of the flights. I think the critical point in here how long of a transect the UAV is covering and what would be the minimum flight speed to achieve this. Since these two can be more or less approximated the spatial resolution can also be approximated with proper flight planning. I think authors need to revise this statement.

Lines 353 – 364, For a better comparison I suggest the authors to remove background from both signals, so that the peaks from the plumes becomes more visible. As I commented above there also seems to be a temporal lag between these instruments which needs to be explained why?

Lines 388 – 390, Maybe using different color for a volcanic plume and contaminated sample will be better to easily differentiate them in the plot.

Lines 395, What do you mean by aged? Do you mean dispersed?

Line 412, Could you please provide more details in here? How sensitive these statistics are?

Line 417, do you mean orthogonal distance regression (ODR)?

Figure 6, I wonder how different the regression line would be when the CO2 measurements from low-cost sensor (after correcting the offset) was used addition to Aircore. This would be interesting to see for researcher relies exclusively on low-cost sensor and don’t have access to a CRDS.

Lines 437 – 439, This needs more discussion in my opinion. According to the flight path provided in Fig S11, the wind direction and flight path in downwind SEC aligns very well compared to VOR one. The flight path that was associated with VOR seems to only captures the plume slightly, probably due to plume meandering and/or dispersion the peak goes down but the flight path from the figure cannot capture the entire plume extent from VOR, hence the comparison as is done would not be representative. Also, some explanation is needed why the first flight path in downwind SEC do not see any of the plume? Maybe due to flight altitude and plume rise, but this should be discussed and ideally plotted in the figure.

Lines 439 – 440, Similar problem also occurs in here, according to wind direction shown in the figure, the observed plume is less likely to be originated from these craters. Some of the detected peaks seem to coming somewhere from upwind rather than downwind. Could there be another vent or source?

Line 461, this sentence is not clear, what does still new Aircore mean?

Technical comments
Figure 3, Aircore are highlighted by the the brown bar, remove the double "the” in here.

Line 476, Thus is is …, correct this typo please.

References
Kunz, M., Lavric, J. V., Gerbig, C., Tans, P., Neff, D., Hummelgård, C., Martin, H., Rödjegård, H., Wrenger, B., and Heimann, M.: COCAP: a carbon dioxide analyser for small unmanned aircraft systems, Atmos. Meas. Tech., 11, 1833–1849, https://doi.org/10.5194/amt-11-1833-2018, 2018.
Bonne, J.-L., Donnat, L., Albora, G., Burgalat, J., Chauvin, N., Combaz, D., Joly, L. (2024). A measurement system for co2 and ch4 emissions quantification of industrial sites using a new in situ concentration sensor operated on board uncrewed aircraft vehicles. Atmospheric Measurement Techniques, 17 (14), 4471–4491. Retrieved from https://amt.copernicus.org/articles/17/4471/2024/534.
Bolek, A., Heimann, M., & G¨ockede, M. (2024). UAV-based in situ measurements of CO2 and CH4 fluxes over complex natural ecosystems. Atmospheric Measurement Techniques, 17 (19), 5619–5636. doi: 10.5194/amt-17-5619-2024.
Dooley, J. F., Minschwaner, K., Dubey, M. K., El Abbadi, S. H., Sherwin, E. D., Meyer, A. G., Follansbee, E., and Lee, J. E.: A new aerial approach for quantifying and attributing methane emissions: implementation and validation, Atmos. Meas. Tech., 17, 5091–5111, https://doi.org/10.5194/amt-17-5091-2024, 2024.
van Hove, A., Aalstad, K., Lind, V., Arndt, C., Odongo, V., Ceriani, R., Fava, F., Hulth, J., and Pirk, N.: Inferring methane emissions from African livestock by fusing drone, tower, and satellite data, Biogeosciences, 22, 4163–4186, https://doi.org/10.5194/bg-22-4163-2025, 2025.
Bolek, A., Beattie, M. N., Norooz Oliaee, J., MacLeod, R., Skeeter, J., Morse, P., G¨ockede, M. (2026). Application of uav-based methods for quantifying methane point source emissions over an arctic geological seep. Atmospheric Measurement Techniques, 19 (12), 3983–3998. Retrieved from https://amt.copernicus.org/articles/19/3983/2026/ doi: 10.5194/amt-19-3983-2026.
Beattie, M. N., Sun, C., MacLeod, R., Sabourin, N., Morse, P. D., Smallwood, G. J., Corbin, J. C., and Norooz Oliaee, J.: Ultra-Lightweight Mid-IR Methane Sensor for UAV-based Measurements, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2026-137, 2026.

Reply
Citation: https://doi.org/10.5194/egusphere-2026-1865-RC1
- CC1: 'General statement on RC1', Johannes Degen, 10 Sep 2026 reply
  
  We thank the reviewer for the thorough reading of the manuscript and for providing valuable and very detailed feedback. We would like to take this opportunity to briefly respond to and comment on the reviewer’s general feedback directly:
  We recognize that our presentation of the study’s novelty may have been overstated, and we agree that this point requires further clarification. While a few active AirCore studies have already been published (introduction of the method itself, different technical adaptations and applications), we believe that our study represents a relevant methodological advancement of the technique. The newly introduced pressure correction enables a more altitude-independent sampling approach, as also noted in the reviewer’s feedback. This extends the applicability of the technique beyond sampling at a fixed altitude level closely linked to the launch location and thereby substantially broadening the range of potential applications. We agree that this improvement is somewhat overshadowed by the “volcanic plume” application in the manuscript and could be presented in a different way.
  Our study provides a direct comparison of the performance of AirCore and low-cost sensors, which can help to better assess the potential and limitations of both approaches and to identify where further technological development is needed. We fully acknowledge that the way in which the comparison was conducted can be further improved, particularly with regard to a more quantitative assessment. In this context, we would like to thank the reviewer once again for the helpful specific comments. We look forward to incorporating these suggestions into the revised manuscript to better highlight the value of this comparison and more fully realise its potential.
  
  Reply
  
  Citation: https://doi.org/10.5194/egusphere-2026-1865-CC1

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Active AirCore trace gas measurements at Mount Etna from the 2024 EarthCriSys campaign Johannes Degen et al. https://doi.org/10.5281/zenodo.18983895

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Short summary

Observations in volcanic plumes often rely on Uncrewed Aerial Systems (UAS). In July 2024, we used the active AirCore technique with UAS to probe the plumes of Mount Etna (Italy). This was the first time to use this technique inside volcanic plumes. AirCore samples are stored in long coils for laboratory analyses delivering high-quality trace gas measurements. We observed enhanced mole fractions of CO₂ and often also of CO. allowing conclusions on oxidation processes inside the crater.


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