the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Feb 2026
Volcanosonda: A Novel, Lightweight and Low-Cost Instrument for In-Situ Characterization of Volcanic Clouds – A Cross-Comparison Experiment
Abstract. Retrievals of volcanic clouds generated by eruptions are essential for effective emergency management. However, current methods have significant uncertainties due to the challenges of accurately measuring certain critical parameters through remote sensing. To address this, a new lightweight and low-cost multi-gas sensor instrument, called Volcanosonda, has been developed. It is designed to be deployed into volcanic clouds using sounding balloons, enabling in-situ measurements to enhance the characterization of these critical parameters. This work presents the measurements and cross-comparison results from an experiment conducted on Vulcano Island using the Volcanosonda alongside four well-established multi-gas sensor instruments. The results show an overall agreement between the measurements of SO2 and CO2 and the estimated CO2/SO2 ratios.
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Status: open (until 02 Apr 2026)
- RC1: 'Comment on egusphere-2026-226', Anonymous Referee #1, 25 Mar 2026 reply
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RC2: 'Comment on egusphere-2026-226', Anonymous Referee #2, 28 Mar 2026
reply
Manuscript: Volcanosonda: A Novel, Lightweight and Low‑Cost Instrument for In Situ Characterization of Volcanic Clouds – A Cross‑Comparison Experiment
Authors: Naranjo et al.Summary
This manuscript describes the development and initial evaluation of Volcanosonda, a lightweight, low‑cost in‑situ gas and aerosol measurement package for balloon-borne deployment in volcanic plumes. The authors present a general overview of the system and report ground‑based measurements from Vulcano alongside data from four co‑located portable multigas instruments.
The balloon‑borne sonde concept is interesting and potentially relevant for advancing volcanic‑plume studies. The manuscript is appropriate in scope for Geoscientific Instrumentation, Methods and Data Systems. However, the current version lacks technical rigor and requires substantial clarification and contextualization. The experimental results merit publication, but major revisions are necessary before the manuscript can be considered further.
Recommendation: Major Revision
The instrument concept is valuable, but significant methodological and contextual improvements are required. More comprehensive and clearer descriptions of the developed instrument, its intended use, calibration procedures, sensor performances, and acknowledgements and discussion of limitations of applying low-cost sensors to volcanic plume studies will greatly strengthen the manuscript.
Major Comments
- Technical Description of Volcanosonda
The technical description is inadequate for a method‑focused manuscript. Fundamental details of the pneumatic, electrical, and data‑acquisition architecture are missing. The manuscript provides only high‑level component descriptions, and the cost and weight‑reduction rationale is not well supported.
Please address the following:
- Provide diagrams showing the pneumatic, electrical, and data‑flow architecture.
- Clarify the intended operating environment (tropospheric plumes, stratospheric plumes, broader research vision).
- Specify telemetry range under typical plume conditions.
- Report sensor resolution, detection limits, and expected measurement uncertainty.
- Describe materials and components used, including how mass and cost were reduced.
- Explicitly discuss tradeoffs associated with low‑weight, low‑cost design (e.g., durability, analytical characteristics, etc).
- State whether the instrument is intended to be disposable, and discuss operational and environmental implications.
Additionally, the current instrument descriptions are fragmented across multiple tables. A single consolidated comparison table summarizing all instrument parameters (measured species, sampling rate, dimensions, weight, cost, resolution, range, etc.) would greatly improve clarity and allow readers to better understand the pluses and minuses of the various systems.
- Calibration Procedures and Analytical Performances
The calibration section lacks the detail required to evaluate instrument performance. Table 1 is unclear, and the rationale for showing only SO₂ is not explained. The calibration approach for CO₂ and other sensors is not described.
Specific issues that require revision:
- Provide full calibration procedures, including gas standards used, concentrations, accuracy, altitude/pressure corrections, and any laboratory/field checks before and after deployment. What was done before and after the deployment to assess the sensor performances?
- Explain calibration workflows for all sensors, including CO₂.
- The manuscript relies heavily on manufacturer specifications; report what was done to verify these claims, especially given that plume RH and temperature often exceed manufacturer limits.
- Volcanosonda is described as measuring ambient temperature and RH, but these data are not shown. They are essential for interpreting gas and aerosol measurements and must be included.
- Clarify whether the CO₂ sensor’s digital filter was used and at what setting.
- Aerosol Measurements
The manuscript does not adequately acknowledge the known limitations of low‑cost aerosol sensors. Over the past decade, numerous studies have documented issues with size discrimination, RH sensitivity, and inaccurate coarse‑mode mass reporting. The authors do not cite this literature or address its implications for the instrument.
Concerns requiring attention:
- Provide a literature review summarizing known limitations of low‑cost PM sensors and justify the choice of sensor used in Volcanosonda.
- The specific PM sensor used is known to have poor performance for coarse aerosol modes; this limitation must be acknowledged.
- The manuscript’s conclusion that “optical particulate matter have an optimal performance” is not supported by the evidence presented and contradicts existing literature.
- The authors highlight volcanic aerosols as a public‑health hazard but do not acknowledge the risk of misinterpretation when size‑distribution data are inaccurate.
- The PM measurements need substantial reframing to avoid overstating performance.
- Validation against a reference PM method or additional evidence demonstrating sensor behavior in volcanic conditions is strongly recommended.
- Study Setup
The study is weakened by the absence of a reference instrument. In the absence of a reference-quality instrument to validate the low-cost sensors’ performances, the authors should compare Volcanosonda measurements to the ensemble mean of the co‑located instruments to provide a meaningful relative‑performance assessment.
Performance claims should be reframed as follows:
- Use ensemble comparisons to evaluate relative, not absolute, performance.
- Avoid the term “accuracy” unless traceable calibration is demonstrated.
- Provide uncertainty estimates and discuss environmental factors affecting measurement stability.
Minor Comments
- The abstract is vague: e.g. l.17 “…certain critical parameters” – which critical parameters? And again, l.21 “…these critical parameters.” Which ones? Please be specific and clear.
- Section 3.1.2: the instrument heading says “MiniGas NTX-PRO” while the Figure says “MiniGAS PRO-NTX” – pick a capitalization scheme and name and be consistent.
- The manuscript states the PP Systems SBA-5 has (l.43) a “solid state water vapor pressure sensor” – this is not really correct. The SBA-5 uses an RH sensor to measure water vapor and reports the data in terms of partial pressure.
- 47: “…away from the drone’s core…” What drone? Were drones used in this study? The intercomparison is presented as being ground based.
- Much of the instrument descriptions read like commercials: (l.80) “…within a user-friendly and reliable setup”, (l.196) “With its compact design, precise measurements, and ease of use…”, etc. Please edit these descriptions to be neutral, factual, and supported by data and references within the manuscript.
- 228: this is a verbatim repeat from the previous section (l.199).
- Section 4.2: the explanation given for the CO2 discrepancies is that the “sampled gas was not identical across instruments”. Why then, does the SO2 data show better agreement? This explanation is not internally consistent. Please clarify.
- The CO2 sensor responses seem very different. These should be quantitatively described using the calibration peaks. What are the response times? Shapes (1st order, 2nd order, etc.)? This topic needs to be clearly addressed, and the information should be included for every instrument to demonstrate their similarities and differences. It’s important to have fast sensor responses, especially for drone-borne (and presumably balloon-borne) sensing systems.
- Why were the data shifted to align the peaks? What justifies this approach? Did the field-based sensor responses resemble the lab-established responses?
- Table 6: edit to include only decimals (it’s a mix of decimals and commas)
Citation: https://doi.org/10.5194/egusphere-2026-226-RC2 -
RC3: 'Reply on RC2', Anonymous Referee #2, 28 Mar 2026
reply
See Rueda et al., 2023 (and references therein) for more information on the accuracy of low-cost PM sensors, including the unit integrated into Volcanosonda. They concluded that "low-cost aerosol sensors (1) cannot discriminate particle size accurately and (2) only report linear and precise measures of aerosol concentration in the accumulation mode size range (i.e., between 0.1 and 1 μm). We recommend that crowdsourced air quality monitoring networks stop reporting coarse (PM2.5–10) mode and PM10 mass concentrations from these sensors. " Nothing from this extensive literature is ccited and potential problems with the sensors integrated into Volcanosonda are never acknowledged or discussed.
Instead, the authors conclude that “…the optical particulate matter have an optimal performance. Our results are encouraging and our new Volcanosonda instrument is ready for deployment into larger volcanic clouds and helping to enhance the retrieval of volcanic clouds.” This conclusion is poorly founded and is not supported by the literature or data presented in the manuscript.
Emilio Molina Rueda, Ellison Carter, Christian L’Orange, Casey Quinn, John Volckens, 2023 Size-Resolved Field Performance of Low-Cost Sensors for Particulate Matter Air Pollution, Environmental Science & Technology Letters, Vol 10/Issue 3, https://pubs.acs.org/doi/10.1021/acs.estlett.3c00030
Citation: https://doi.org/10.5194/egusphere-2026-226-RC3
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- 1
I will not refer to specific line numbers, as my comments address broader issues that appear throughout the manuscript. The article presents a new multigas instrument, the Volcanosonda, intended to be lightweight and compact for future sounding‑balloon applications. Given that this journal focuses on technical instrumentation, the description, characterization, and validation of the instrument must be treated with greater depth and rigor than is currently provided.
Because this work aims to present a novel instrument within an instrumentation-focused venue, the technical description must be central and comprehensive. Several key aspects require clarification or additional detail.
– Need for a schematic
The photographs in Fig. 2 should be complemented with a schematic diagram showing the internal sensor layout, sampling pathway, airflow configuration (if any), and system architecture. This is essential for reproducibility in an instrumentation journal.
– Gas sampling method not described
The manuscript does not specify whether the instrument uses active sampling (pump) or passive diffusion.
Related details are also missing:
This information is critical for understanding sensor response times, plume interaction, and comparability with the other instruments.
– Response time and harmonization of CO₂ vs. SO₂
The authors note that the CO₂ signal shows a noticeable delay relative to SO₂, but no T90 response times are reported for either sensor.
Given the journal’s focus, the manuscript should clarify:
– Calibration procedures require greater rigor
The SO₂ calibration is not described at a level suitable for a technical instrumentation paper. Table 1 lists several measurements but does not provide:
Applying a single mean percentage error (~18%) is not equivalent to establishing a valid calibration function and may obscure systematic effects. A more rigorous calibration section is necessary to ensure traceability and reproducibility.
– Cross‑sensitivities
Electrochemical SO₂ sensors, as the model used here, have known cross‑sensitivities to gases such as CO, NO, and NO₂. Even if the effect of these gases is expected to be minor at this site, the issue should at least be discussed, given the implications for accuracy and inter‑instrument comparison.
– Separation between experiment and discussion
The experiment description and the interpretation of results are mixed up, making the narrative difficult to follow. For clarity, these should be presented as distinct sections.
– Length of complementary instrument descriptions
The descriptions of complementary multigas instruments are very long and sometimes overshadow the presentation of the Volcanosonda itself. Streamlining these sections to include only the necessary comparison‑relevant details would improve focus.
– Editorial and language clarity
Even when I am not a native English speaker I think that the manuscript would benefit from editorial polishing. Some transitions are abrupt, and several paragraphs shift topics without clear linkage. Improving these aspects would enhance readability.
Summary
The manuscript introduces a lightweight multigas sensor platform; however, the technical detail, sampling description, calibration rigor, and discussion of sensor behavior must be expanded and clarified to meet the expectations of an instrumentation-focused journal