the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jun 2026
A new Profiling Optical Particle Counter to study stratospheric aerosols
Abstract. Stratospheric aerosols play key roles in the radiative and chemical balance of the atmosphere, especially after volcanic and wildfire activities. The sources of stratospheric aerosols have become more complex over the last decade through the influence of Asian pollution, rocket and satellite debris, which could be further enhanced with the potential use of stratospheric aerosol injection under solar radiation management. Knowing stratospheric aerosol size distribution is a fundamental step toward calculating and evaluating their radiative, chemical and climate impacts and validating and/or constraining satellite observations.
We describe here the adaptation of the new lightweight, medium-cost Profiling Optical Particle Counters (POPC) for weather balloon applications. Over the past 8 years, the POPC design and capabilities evolved from a handheld version with 6 channels (POPC-06) to a compact 500g-version with 30 channels measuring aerosol optical diameters between 0.3 to 10 µm. POPC-30 aerosol concentration for d >0.3 µm. is shown to be within 20% of the Portable Optical Particle Spectrometer (POPS), correlates near 0.97 with the COmpact Backscatter AerosoL Detector (COBALD) and lies within 50% of the extinction coefficients retrieved from highly accurate solar occultation measurements from the Stratospheric Aerosol and Gas Experiment (SAGE III/ISS). With 87 flights since 2018, POPC demonstrated its capabilities to detect volcanic plumes after the 2019 Raikoke, 2019 Ambae, 2021 La Soufriere, 2022 Hunga and 2024 Ruang eruptions and was deployed rapidly to intersect pyroCb smoke plumes in the Northern Hemisphere. The instrument is currently launched by several universities and research institutes in Brazil, India, France and the US as a part of the Balloon Network for stratospheric aerosol Observations (BalNeO) complementing other measurement networks. POPC data set is publicly available to the research community for various applications ranging from boundary layer aerosols to free tropospheric and stratospheric aerosol microphysics.
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Status: final response (author comments only)
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RC1: 'review on egusphere-2026-3280', Ralf Weigel, 16 Jul 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3280/egusphere-2026-3280-RC1-supplement.pdfCitation: https://doi.org/
10.5194/egusphere-2026-3280-RC1 -
AC1: 'Reply on RC1', Jean-Paul Vernier, 07 Aug 2026
Dear Ralf,
Thank you for taking the time to review this paper. I really appreciate even if your 15-page review will occupy me quite a bit….Before preparing a full review, I wanted to provide a short answer on the main points you made in your review.
- Explain how the POPC device was converted into a balloon-borne system
Yes, I agree that we should spend more time explaining the process of converting a ground-based system for balloon applications and stratospheric measurements. I will dedicate a section to provide more details on the different steps.
- Clarify why we moved from POPC-06 to POPC-30
The move from POPC06 to POPC30 was a natural step toward the conversion process of the POPC for balloon applications. Further explanations will be provided in the revised manuscript.
- Mie Theory to be clarified, solid angle versus full scattering.
We will re-write the equations to clarify that all the calculations made in the theoretical section are indeed within the scattering angle between 58˚ and 108 ˚.
- Provide a better explanation of how the calibration with the SMPS is done
The POPC is calibrated by our commercial partner (Particle Plus, Inc.) but can definitively provide more detailed information on the set up they use for calibration.
- Error analysis
Yes, we can provide additional information on how the error analysis is indeed used to derive an error bar on the POPC data.
- Section 3 should be restructured to improve the thread
We will work on improving section 3, which is indeed the core of the paper.
- Comparison between POPC and POPS size distribution should be done
This will be done.
- Overrepresentation of the data? Select a few cases, Pyrocb, volcanic plume and background
We appreciate the fact that you recognize that an enormous effort has been made to gather data across the world with this instrument to test it in various conditions to evaluate its performance. I would argue that this is not an overrepresentation of the data but rather a comprehensive testing phase. We can indeed emphasize a few cases in this paper but showing a summary of all the measurements made as discussed in section 4 provides the reader with an idea about instrument’s performance under different conditions in which some limitations can be also explained.
Citation: https://doi.org/10.5194/egusphere-2026-3280-AC1 -
RC2: 'Reply on AC1', Ralf Weigel, 11 Aug 2026
Dear Jean-Paul.
Please believe me, I would have preferred to keep this review well below this page count. But thank you very much for being willing to consider made suggestions.- overrepresentation of data versus comprehensive testing phase:
In this context, however, the presented data should primarily be discussed from a technical perspective with regard to the performance of the measuring instruments; that is, through comparisons with other measuring instruments that generated data simultaneously during the observation phases, or through a discussion of, e.g., temporal variability, or similar.
In my view, this part of the submitted manuscript focused primarily on presenting data regarding specific events or locations and did not clearly address the associated technical aspects (e.g., data consistency, internally and in relation to alternative, collocated measurements). The sheer volume of data presented is OK, provided that information on the performance of the measuring instruments is extracted and the technical aspects are not sidelined.I wish you all the best as you move forward with the publication process.
Citation: https://doi.org/10.5194/egusphere-2026-3280-RC2
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AC1: 'Reply on RC1', Jean-Paul Vernier, 07 Aug 2026
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RC3: 'Comment on egusphere-2026-3280', Anonymous Referee #2, 13 Aug 2026
General comment:
This article describes the development and deployment of a balloon-borne OPC designed to measure aerosol size distributions in the stratosphere. The instrument was developed in two stages: POPC-06, with 6 size channels, which later advanced to POPC-30, with 30 sizing channels. POPC instruments have been flown extensively, and the results from these flights are presented in this manuscript. There is a brief description of the POPC instrument, followed by a description of the calibration and flight-worthiness test procedures. Comparison flights of POPC to other OPCs are then presented, as well as a comparison of a derived aerosol extinction product to measurements from SAGE III. Finally, a very general overview of the observation history of POPC is given. Overall, the manuscript lacks the detail needed on the instrument development process. The comparison to other instruments is well done and is a strength of the paper. The section overviewing the science is thin and not thorough enough to provide useful insight to the reader. This paper needs significant work before publication.
Specific comments:
(1) My main concern with this manuscript is that it does not describe the instrument in sufficient detail for an instrument paper. For example, how was the commercial device made suitable for deployment on high-altitude balloons? How is the thermal environment controlled? What about data management? A better diagram and/or picture of the instrument would help the reader understand what the POPC instrument is. It is mentioned that the counting efficiency of POPC was determined using the SMPS, but the specifics of this are not given. Further, how do the authors know these counting efficiencies remain consistent over the flight domain in the stratosphere, where temperature and pressure change significantly? What is presented is a brief description of the technical specifications of a commercial OPC that was modified in an unspecified way to be flown on a balloon.
Another example of missing detail is in Section 3.2, on flow analysis. Line 304 states, "We use this information to derive the relative error in flow that we incorporate into an error analysis in the next section." How is the relative flow error derived? (Also, the term Q is never defined.) Generally, I found the description of the flow analysis and Mie calculations confusing. More detail on the steps the authors took to compute aerosol size distributions and extinction coefficients would be beneficial.
(2) A significant concern with the design of POPC is that the instrument does not appear to have any sort of sheath flow around the sample air as it enters the optical chamber where it is sampled by the laser. How do the authors know there is no divergence of the sample air beam within the optical head across the pressure range in which the instrument operates? POPS, to which POPC is compared in this paper, is known to suffer from similar beam-divergence issues at low pressures. This relates back to the point above about how the counting efficiency is determined: how do the authors know that this characterization of POPC, done at the surface, remains valid in the low-pressure environment of the stratosphere? There is likely a good answer to this question, but the reader is left to guess, as there is insufficient detail about the POPC development process given in the paper.
(3) The introduction could be more specific about what problem is being solved or addressed by the development of POPC. Section 1.3 overviews current OPCs that operate in the stratosphere (though I question the inclusion of LOAC, as it has not been demonstrated that it can measure stratospheric aerosol, a point the authors themselves make), but it does not explain how the addition of POPC will better address any longstanding scientific questions about stratospheric aerosols. For example, both solar radiation management and anthropogenic stratospheric aerosol sources from rockets and satellite reentry are mentioned as new sources of aerosols. These sources are not discussed anywhere else in the manuscript. Can POPC be used to quantify the impact of these sources on stratospheric aerosol?
(4) Perhaps present the percent error when comparing POPC to other OPCs on a linear scale? Using a log scale makes it hard to see errors in the 20–40% range.
(5) Section 4, Science Results & Interpretations, could benefit from expansion. It is little more than an accounting of when POPC has observed some sort of aerosol plume event in the stratosphere. Is there a way to add more context to these measurements so that the observed features have more significance to the reader? The authors could show size distributions from different plumes to compare particle modes across different layers, or compare volcanic, non-volcanic, and pyroCb-influenced aerosol and discuss how these size distributions influence optical extinction. Time series plots and a map of the balloon launch sites would also be useful for illustrating the influence of the volcanic events on aerosol concentration in the stratosphere as observed by POPC. It is difficult to compare and interpret the profile plots in Figure 13, which show how aerosol concentrations have changed due to aerosol events.
Most importantly, what is new in these results that has not already been reported? Is it simply that these are measurements from a new instrument? Related to comment (3), what new scientific insight is being gained from the POPC measurements? Or how do they agree with other aerosol measurements of the same features? Many OPCs have measured aerosol enhancement from the discussed volcanic eruptions — how do those measurements compare to what is observed by POPC? These are just examples of how Section 4 could be made more relevant to readers.
Further, I don't understand why the paragraph starting on line 568 is included. It simply repeats aspects of the development history of POPC that have already been stated and lists encounters POPC has had with aerosol events. What is the value or interest to the reader here?
(6) The writing and presentation quality are currently insufficient for publication. For example, multi-panel figures are missing labels (see Figure 9). Equation 6 appears to be a screenshot of an equation from a different text. Numerous grammatical and formatting issues occur throughout the text (see lines 170 and 398), file names are used as figure titles, etc. This reads more like a draft than a polished manuscript. Please have the author team do a more thorough editing of the manuscript.
Technical corrections:
I won't list specific corrections, as there are many that need to be made, and the text is likely to change significantly if the changes above are addressed.
Citation: https://doi.org/10.5194/egusphere-2026-3280-RC3
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