General comment

Pohorsky et al. present in their manuscript a newly developed tethered balloon platform for in situ measurement of atmospheric aerosol particles and trace gases. With a helikite and a modular suite of instruments, the so-called MoMuCAMS system can provide observational capabilities for particle microphysical and chemical properties in the lower troposphere. Development efforts were taken to allow deployments in challenging environments like the polar regions. Airborne measurements of aerosol vertical distributions are highly relevant for various studies and model evaluations, particularly in remote regions. Therefore, the work can potentially add a valuable contribution to the atmospheric measurement community and is suitable for publication in AMT after major revisions.

Parts of the manuscript need to be rewritten and restructured to improve readability. More accurate descriptions and carefully selecting synonyms should be considered to achieve correctness. The introduction, methods, and results sections can profit from a clearer separation; for instance, no results in the method section or background in the results section. The possibility of providing information not directly related to the platform within the supplementary should be considered. Conversely, some methodical details should be provided with the main manuscript instead of the supplementary. Comparisons of the mobile instruments of the platform with stationary instruments over a longer time range should be added for all instruments to prove the platform’s capacity to provide quality-assured data. The authors are encouraged to resubmit after a comprehensive revision.

Detailed comments

Abstract

Length should be reduced to the important content of the paper, redundancy should be avoided, and aspects not shown in the paper should not be claimed.

Since this is a technical paper, the focus should be on instrument performance and not too much on the case studies.

Line 17: “multiplatform compatible” is redundant since it is part of the platforms name and abbreviation

Line 19: add “atmospheric” before boundary layer

Line 19 to 21: “These regions are known to …” no background is needed here and the properties are not specific for the mentioned regions

Line 24 to 27: “This flexibility …” this sentence seems inaccurate because the multiple aerosol properties can only be measured in different configurations and not simultaneously. “cluster ions” and “optical properties” measurements were not shown in the paper. Chemical analysis is done offline, it’s basically a balloon-borne filter sampler provided with the subsequent analysis being free to the user/application.

Line 27: “To the author’s knowledge,…” should be avoided, leave it to the reader to decide

Line 28: “full size distribution” is inaccurate, smaller and larger particles exist beyond the observational range, you can use “wide range” instead. The upper end of the size range should be mentioned and precisely define if you mean number or volume or surface size distribution

Line 32: the Finland campaign is actually not shown in the manuscript

Line 34: -36 °C and winds up to 15 m/s are not shown in the manuscript and shouldn’t be claimed without prove

Line 35: “full characterization” seems inaccurate; full might mean something else for the authors than for others, and some important parts of the characterization are actually missing (see below)

Line 42: seems inaccurate, after the development of a mixed ABL there is no surface layer anymore

Line 50 to 52: seems inaccurate, the presented system is not capable of capturing aerosol-cloud interactions. In general, a tethered balloon can only provide a snapshot from one position of a usually moving air mass and has, therefore, only limited process observation capabilities. The measurements always need to be put in context with other observations or modeling to use for process studies.

Introduction

Readability can be improved by restructuring the text to guide the reader only in one direction, from the broad topic of aerosol measurements to the specifics of balloon-borne observations with a technical focus. Jumping forth and back from detail to broad should be avoided

Line 66: What do you mean by “strongly stratified”? Do you mean multiple atmospheric layers or stable stratification? The ABL often features multiple layers and stable stratification, not only in polar or mountain regions.

Line 67: More precision required, stratification is a synonym for layering, do you mean “stable atmospheric stratification”?

Line 75: “However, for assessing the direct and indirect radiative impact of aerosols, knowing their vertical distribution is vital.” was written almost the same in line 63

Line 80 to 83: seems inaccurate, some of the described circumstances only belong to polar regions.

Line 84: “shallow inversions” seems inaccurate, an elevated inversion layer that is in the range of the lidar can also be very shallow. Do you mean “shallow ABL”?

Line 88: “air layers” is very inaccurate, do you mean “atmospheric layers” ?

Line 88 to 89: “Moreover, typically aircraft do not fly within the first hundreds of meters above the ground, missing therefore valuable information”. This statement seems inaccurate. Many different kinds of aircraft can perform manifold flight patterns depending on the research objective, as shown in various studies. The advantage of balloons is that they can provide higher resolution, operate under icing conditions, and be within supercooled clouds for an extended time.

Line 95: seems inaccurate, HOVERCAT is not a tethered balloon system

Line 107: “To the authors’ best knowledge…” see above

Line 109: since the platform is designed for arctic regions, it should be stated that CCN can be well below 100 nm in size

Line 116: “…to be deployed on sea ice” is true, but it is not a proper criterion. Way heavier instruments and infrastructure have been deployed on sea ice. Usually, sufficiently thick sea ice floes are selected for scientific operations

Section 2

Provide the model, manufacturer, and country in brackets behind the devices that occur in the text e.g. helikite (Desert Star, Allsopp…, GB)

Section 2.1

Please provide a more detailed mechanical sketch of the payload enclosure to prove the claimed “flexibility” of the system to accommodate multiple instruments. Figure 2 doesn’t provide enough details on that

Provide measurements of the inner temperature of the box during low-temperature conditions

Line 126 to 127: the paper actually shows the deployment of 8 different instruments in 3 different combinations, I wouldn’t consider this “a very large number of combinations”

Table 1:

- measurements not shown in the paper e.g., the STAP, shouldn’t be part

- add uncertainties

- add weights of individual instruments since it is the limiting factor for possible combinations

- a scientific objective of typical instrument combinations would be interesting

Line 129: “guest instrument” sounds awkward, it is sufficient to phrase it with additional instruments

Line 141: use “transmission” instead of “streamed”

Line 143: “subset of data”, please specify

Line 145: “various instruments”, please specify

Section 2.2

Line 150: what is the maximum length of the tether, including the extension? This is an important limitation of the observational capabilities

Line 154: Please provide a time series of the flight(s) on which the extreme temperatures and wind speeds were observed

Section 3

• Please introduce abbreviations in the text at the first occurrence

Line 165: Only instruments shown in detail in the manuscript should be mentioned, thus delete the STAP

Line 172: Is the 30° bend sufficient for preventing water droplets from entering the inlet? What about the tilt of the tether and the balloon itself at higher wind speeds, can that be up to 30° so that the inlet is actually horizontal? Please discuss

Line 173: Provide a time series that shows the relative humidity behind the inlet is sufficiently reduced by the heating system on a flight in high-humidity environments

Line 197 to 201: The explanation given for the large discrepancy between the 10 cm and 45 cm tubes for 510 and 994 is not sufficient. At the reported average number concentrations of 20 and 35 cm-3, the CPC should not show a deviation up to 25 % at 5 min averaged data. It appears that the measurements were not done properly or the CPCs had a malfunction.

Section 3.2

Line 205: be precise, “particle number concentration”, there are multiple other types of particle concentrations (surface, mass, …)

Line 206: provide the measurement range of the reference CPC.

Line 208: the figure should be part of the main manuscript

Line 210 to 214: This calibration is a fundamental part of ensuring validated measurements. Detailed information about test particles, averaging/comparison time, experimental setup (flow and line lengths), and the resulting plot should be part of the main manuscript. Please explain why there are two measurements for only some particle sizes and not for all. If there were multiple calibration runs, what explains the differences between the two runs, and why was one not done for the entire size range?

Section 3.3.

Line 224 to 227: Please provide more information on the size calibration:

• Calibration setup incl. dryer etc., average particle number concentration, sampling time, number of channels/size resolution of the mSEMS à was it the same as for balloon flights?
• Why wasn’t the full measurement range from 8 to 300 nm calibrated?
• It appears that the sizing uncertainty increased with decreasing particle diameters. A calibration of below 50 nm seems, therefore necessary

Line 227: seems inaccurate, the maximum deviation from the PSL diameter, including standard deviation, is larger than 8 %.

Line 229: Was a dryer used after the nebulizer?

Line 246-247: Is the explanation for the remaining underestimation of about 21% after correction supported by the number size distribution? The contour plots from the case studies don’t seem to show a pronounced accumulation mode above 300 nm, which represents 21 % of the total particle number.

Line 253: what do you mean by “stratified layers” ?

Line 250 to 255: This part rather reflects sampling strategy than instrument methods. Because it also appears in other sections, you should consider one separate paragraph for “sampling strategy”.

Section 3.4

This whole paragraph needs methodological revision:

A deviation of 20 % at 500nm PSL seems high compared to the findings by Mei 2020, Liu 2021, and Pilz 2022. According to Gao 2016, Mei 2020 and Liu 2021, there should be no Mie resonances at 500nm with the POPS. It appears that the instrument was rather not well adjusted or the optics were dirty, resulting in reduced signal intensities. Hence, all subsequent measurements should be taken carefully because all particles detected are actually larger than those measured by the POPS.

This has also an impact on the high noise that you observed in channels below 186 nm. It would mean that the noise of your POPS units is actually up to actual particle sizes of ca. 220 nm, which would be very high compared to previous findings (Gao, Mei, Creamean, Liu, Pilz). In addition, dirty optics can also cause additional straylight leading to a reduced signal-to-noise ratio. The fringes on the Gaussian signal you describe are not a regular behavior of the sensor and are not a sufficient explanation to oppose the previous findings. Your findings significantly reduce the useful size range of the POPS, particularly for your intended measurements in polar regions.

Section 3.5

This whole section provides rather an experience report than an instrument characterization. There is no comparison to other instruments or calibration provided. The investigated impact of environmental conditions on measurements does not say much without a reference, and Figure 4 a) only shows a point cloud. What is the temperature in 4 b) ambient or inside the Pelicase?

What about manufacturer calibration or other publications that show the performance of the instrument?

Section 3.6

Line 313-314: What do you mean by this sentence: “The multiple nozzle-pattern achieves cut-size selection similarly to the more common Micro-Orifice Uniform-Deposit Impactors (MOUDI)”. Is the HFI additionally equipped with a MOUDI, or is it compared to the MOUDI? Why is MOUDI written in brackets behind the instrument in Table 1?

Line 325 to 343: This part does not directly belong to the platform and should be considered as supplementary. The MoMuCAMS system provides a filter sampler, but it depends on the scientific objective and the environment of how the filters are treated and analyzed. Please keep in mind that this is a technical paper about a balloon platform.

Section 3.7

Line 362 to 379: Same as above.

Section 3.8

Table 3: Accuracy is usually given as +-… and please use “to” instead of “-“ for the ranges to avoid confusion with positive and negative values

Line 398 to 400: This is an outlook for future improvements and should be in the according section

Line 390: Please provide more details on how the comparison was done. Was the sensor on the tether or on the ground, distance to the reference station, etc.

Why was the sensor not shielded against direct radiation during comparison? It is common knowledge that temperature sensors are affected by direct solar radiation and are, therefore, always shielded in a weather station.

Section 4

This section can be shortened to focus on the platform's performance. The description of the single case partly suffers from a lack of ABL meteorology knowledge. I suggest focusing more on instrument/platform performance than on atmospheric science, which can only be partly done with the available ground-based and balloon-borne observations.

Please add:

• Internal temperature of the platform and relative humidity of sampled air during flights
• Direct comparison of the mSEMS and the POPS with the ground SEMS in PNSD plots including discussion
• Performance evaluation of the mSEMS in terms of scanning time vs. accuracy, up-scan vs. down-scan, counting statistics in elevated atmospheric layers with low particle number concentrations including implications for measurements in polar regions
• Performance of the inlet inside clouds, e.g. were water droplets entering the inlet?
• Details on how optical PNSD from the POPS is merged with the mobility PNSD from the mSEMS
• Provide information about balloon climb rates and resulting vertical resolution for individual instruments

Line 412: What is a SEMS and what does it measure, mobility diameter? Please be precise with the abbreviation of particle number size distribution, either use PNSD or NSD. PSD could also mean volume or surface size distribution

Section 4.1

Aerosol stratification and mixing usually result from ABL meteorology (besides aerosol direct radiative effects causing thermal layering in polluted environments). Therefore, it is useful to define ABL structure based on meteorological observations and derive aerosol layers from that. The authors should consider the book “An Introduction to Boundary Layer Meteorology” by Roland B. Stull

Line 434: Table 4 is not needed. Name the instruments of which measurements are shown.

Line 440: Figures 10 a) to c) should be considered supplementary since they are not related to the platform.

Figure 11: potential temperature should be used in the context of atmospheric stratification

Please also add a humidity profile, this helps for a more accurate layer definition.

Line 450: introduce N7-186 and be consistent with N>186 or N186 or N186-3370,

Why is the POPS range sometimes given up to 3000nm and sometimes up to 3370nm?

Line 469 to 472: This doesn’t seem reasonable. Wind shear is induced between layers of different wind directions or at the surface. Here, a typical logarithmic wind profile was observed that indicates wind shear at the surface with a change in wind direction (see: Ekmann layer).

The term “decouple” is usually referred to two turbulent atmospheric layers being disconnected by a stable layer. Here, mixing in a shallow surface layer inside the temperature inversion is induced by wind shear in the absence of solar radiation. The layers above are probably stably stratified, hence decoupling from an elevated mixed layer seems not the case.

Line 477 to 479: The convection causes turbulent mixing, which leads to a decrease in stability, not vice versa.

Line 486 to 490: This statement does not fit well. It appears very unlikely that the convection is strong enough to transport particles into the free troposphere from the bottom of the valley surrounded by ca. 1500 m peaks during fall and at the observed ABL conditions.

The phenomenon described by Harnisch could theoretically explain the observed RL during the first profiles. The presented observations do not seem sufficient to exclude this process.

Section 4.2

The ABL meteorology of this case does not seem to be accurately described referring to the book “An Introduction to Boundary Layer Meteorology” by Roland B. Stull

Figure 15:

• should display the entire PNSD that was measured since it was emphasized in the text that this is an advancement
• the POPS and the mSEMS distributions should be shown in different colors due to the different diameters
• x–axis label should contain D opt

Line 559: the ground-based PNSD is probably better suited to determine the background PNSD

Line 563: Please specify why only a part of the ultrafine particles remain in the ABL

Section 4.3

Line 571: How is the desired sampling altitude defined?

Line 573 to 575: This is rather a part of the sampling strategy than a result

Line 576: The tether length was stated as more than 800m, why was sampling performed in the mixed layer?

Line 580: Please provide more details on the aerosol mass concentration calculation from the optical PNSD and discuss sources for the uncertainty of up to 100 % for flight 2

Line 586 to 594: This is rather background information and no result belonging to the platform

Line 600 to 604: The sample flow is actually high for a balloon-borne filter sampler. If the 5 h sampling time in a mixed layer with close-by anthropogenic aerosol sources was almost too low, how do you see the capabilities for sampling in polar regions with one order of magnitude lower aerosol concentrations?

Line 606 to 616: This is no result of this study

Section 5

The section number is wrong

This section should be shortened to summarize the important technical advances of the system to atmospheric measurements, and case studies can be briefly summarized. Keep the focus on the technical paper!

Line 623: measurements of optical properties were not shown, rather a concentration of trace gases was measured than a composition

Line 626: every altitude is relevant to the Earth’s radiative budget

Line 627: high wind speed and cold conditions were actually not shown

Line 632: High data quality was not sufficiently demonstrated, instrument inter-comparisons are missing, and measurement uncertainties are not entirely investigated

Line 633: What about the separate inlet for the filter sampler?

“… deviation below 5% from…” deviation of what?

Line 637: “The manuscript provides a first empirical correction function. ” for what?

Line 639: the used number of channels is not a finding of this study

Line 642: The STAP was not shown at all

Line 649: Pallas campaign was not shown

Line 670: The reliability of the measurements cannot be proven by three case studies. Long-term comparisons along field campaigns should be considered for reliability evaluations

Line 675: What is “high signal to noise data”?

Line 675 to 679: Other airborne platforms proved the same capabilities. Actually, it is probably required to move along with an air mass to observe processes rather than staying at one spot constantly taking snapshots

This manuscript describes a new measurement platform that can be deployed on a balloon/kite to obtain aerosol and trace gas measurements from the surface to 500m above the surface (although I believe the tether can reach 800m).  The platform uses several miniature instruments.  The manuscript describes and characterizes the platform inlet and several (but not all) of the instruments and shows some field data collected using the platform.  I recommend publication after minor revisions.

1. Figure 3 a. Is this for large particles?  The text suggests that the sampling efficiency is only impacted by particles > 2um.
2. Why is there no discussion of the CO2, O3, and STAP instruments? Are there data for the O3 and STAP instruments?
3. How well do the POPS and mSEMS agree in the region of overlapping size (186-300 nm)?
4. I think sections S1 and S2 belong in the main manuscript.

This article details MoMuCAMS, a new instrumentation system that can be deployed on tethered balloons or UAVs to collect vertical profiles of aerosols, meteorological parameters, trace gases, and microscopy samples. The article details the instrumentation that composes the MoMuCAMS and presents field results from three locations. Publication is recommended after minor revisions.

Line 65, remove comma

Line 94:101, refer to these as instruments not tethered balloon systems or UAVs. The current reference to these as tethered balloon systems indicated that the author is refering to developments in flight platforms rather than the instrumentation packages.

Line 114, quantify windy. Aerostats are advertised to operate in hurricane force winds.

Line 115, if you list balloon setup it should be better defined

Line 135, since earlier in the paper you state that tethered balloons are not as bounded by UAVs in flight time, quantify the expected operating time and the Ah of the batteries

Line 150, the line length is referenced as 800m but the highest mean altitude presented in Table 5 is 434m, which would indicate a steep tether angle. Since the authors promote the helikite as a tethered balloon system due to flight in stable winds, a discussion of the expected tether angle would be beneficial. In general, if the authors are claiming the helikite excels as a tethered balloon system, the flight characteristics of the platform throughout the experiments should be detailed or these references in the publication should be removed.

Line 154, what location is referred to for these ranges?

Line 172, prevents

Line 404, the authors should quantify low and high

Line 496, is 13d really the balloon altitude, or the sensor package? How is the altitude measured and what is the expected accuracy?

Line 519, this sentence should be reworked

Line 629, the authors frequently reference stability. How is this defined and where are these results presented? The authors also reference leakage from the internal membrane below -20 °C but refer to operating at -36 °C. It would be informative to better quantify the helium loss below -20 °C in comparison to higher temperatures if the authors frequently want to reference these statistics as advantageous to the helikite.

In general, since the authors frequently reference that this system can measure at lower particle diameters than other systems, this work seems to somewhat arbitrarily dismiss all data in the three lowest POPS size bins. More support for the exclusion of all three bins should be provided, especially since these bins typically represent the most commonly encountered particle sizes in most environments.

All Figures, since the authors made observations at multiple locations it would be beneficial to include the location in the plot or captions. Especially since the authors reference local emissions sources.