GENERAL COMMENTS

The study by Barreto et al. compares estimates of plume height during the Tajogaite eruption in 2021 derived from two independent approaches: one based on video-surveillance cameras and the other on ground-based remote-sensing profiling instruments. The temporal evolution of plume height is further examined in relation to ancillary measurements. The implications of plume height overestimation for satellite-based SO2 retrieval algorithms are considered, and plume altitude estimations from the surface are compared with CALIOP observations.

The manuscript presents a substantial amount of material, and the overall analyses appear solid and convincing. However, the paper lacks a clear articulation of the specific research questions, which makes it somewhat difficult to follow and gives the impression that the central thread of the study is not fully established. In addition, a more detailed discussion of the uncertainties associated with each technique would strengthen the comparison of results. Overall, I would recommend publication once these issues have been adequately addressed.

SPECIFIC COMMENTS

1. Research questions – Please state the main research questions explicitly in the Introduction, and organise the manuscript accordingly. In addition, highlight the novel aspects of the study in relation to the abundant literature on the same eruption already cited in the bibliography.

2. Algorithm consistency – If I understand correctly, different algorithms were used to estimate plume height from profiling instruments. Why was a single, uniform algorithm not applied, which would have enabled a more consistent comparison?

3. Uncertainty – A thorough discussion of the uncertainties associated with plume altitude retrievals from the different methods is essential before drawing comparisons. Without this, the statement that the results are "highly consistent" (lines 393–394) is difficult to justify. Moreover, it is unclear whether plume height is always defined as the altitude of the plume top, or alternatively as the altitude corresponding to a maximum in the signal. Please clarify.

4. Modulating factors – The discussion of the relationships between plume height and ancillary variables is predominantly qualitative. Are there any models, even empirical ones, that could provide more quantitative estimates of plume altitude as a function of the parameters considered?

5. CALIOP – An average overpass distance of 61.7 km appears rather large for direct comparison with CALIOP. How far is the plume expected to be horizontally transported under the observed conditions? Furthermore, what are the results of the CALIOP aerosol typing? To which aerosol class is the layer attributed?

6. Emissions – Is there any means of determining whether the new estimates of SO2 emissions based on measured plume altitude provide an improvement over the default values?

7. Terminology – The comparison of methods is presented largely in terms of institutions (i.e. IGN vs AEMET–ACTRIS). While this may be relevant for the authors, readers are likely to be more interested in the distinction between techniques, namely video-surveillance cameras versus ground-based profiling instruments. I would recommend revising the subscripts of the variable names accordingly.

TECHNICAL REMARKS

• Abstract – Please state why plume height determination is important already in the abstract.
• Line 2 – Replace "volcanic event" with "eruption" on first mention.
• Lines 6–7 – The phrase "in collaboration" is repeated.
• Line 17 – The phrase "different scientific perspective" is vague. Please clarify what the different perspective entails.
• Lines 22–25 – Are SO2 and the aerosol vertical profiles expected to be similar in proximity to the source? Please, explain the reason in the manuscript.
• Introduction – The section is rather wordy. Some paragraphs could be shortened, retaining only information directly relevant to the scope of the manuscript.
• Line 38 – The expression "conversion process from primary to secondary aerosols" is unclear. The preceding text refers to gas-to-aerosol conversion, not aerosol-to-aerosol processes. Please clarify.
• Line 44 – "significantly longer": is this due to particle size, or to chemical composition? Please specify.
• Line 47 – Bibliographic references are required.
• Lines 83–91 – Given the large number of existing studies, the novelty of this work should be highlighted more clearly. The statement that "this study aims to present the unprecedented instrumental coverage..." is too generic. This would be the ideal point to explicitly state the scientific questions that remain open and will be answered here.
• Line 106 – Rather than emphasising the different networks, it may be more informative to highlight the differences between techniques, as noted above.
• Line 113 – Consider starting the sentence with "The eruption began...".
• Lines 118–120 – As this is key information, it could also be included in the abstract.
• Lines 121–126 – These lines are only loosely connected to the paper's focus and could be condensed.
• Lines 127–131 – This paragraph might be better placed earlier in the event description.
• Section 3.1 – Please clarify whether the reported technique was developed specifically for this study or if it has been described previously.
• Figure 1 – It may be useful to explain why the grid is slightly tilted relative to the figure margins.
• Figure 2 caption – “LA” → “La”.
• Line 191 – "in record time" is too informal. Instead, state the precise number of days.
• Section 3.2 – Please homogenise the terminology for instruments (e.g. ceilometers vs lidar ceilometers) or explain why you keep the naming different. Note that ACTRIS currently uses "Automatic low-power lidars and ceilometers (ALCs)" or, more generally, "Automatic lidar ceilometers (ALCs)".
• Line 272 – As vertical resolution is an instrument characteristic, this should be mentioned directly after "backscattered signal" in the same sentence.
• Lines 274–277 – Were the profiles corrected for overlap? Please clarify.
• Line 282 – "sharp gradients" – do you refer specifically to negative gradients? Please specify.
• Lines 292–293 – Why is this algorithm different? Was it validated against the others?
• Line 292 – The "temporal evolution of attenuated backscatter profiles" does not appear to require retrievals. Are the authors instead referring to the identification of aerosol layer tops?
• Line 306 – Wording suggestion: "... pre-calibrated at the Vaisala facilities using liquid water clouds...".
• Line 311 – Why are only six cases considered? Please explain.
• Lines 357–362 – As this mission ended on 1 August 2023, this paragraph should be written in the past tense.
• Line 364 – The term "loading" is ambiguous. Does it refer to emissions or concentrations? Similarly, "budgets" (line 384) is unclear. Lines 373–375 could be moved earlier to clarify the product description.
• Section 4.1 – As noted above, it may be clearer to separate the discussion by technique rather than by research group.
• Figure 4 – Given the evident variability in plume height, short-term fluctuations (line 389) should be discussed in greater detail. To better assess the agreement/differences in altitude estimates, consider splitting Figure 4 into two or more panels covering different time intervals.
• Line 396 – Please specify when the maximum difference occurred. Similarly, indicate when the minimum occurred (line 397).
• Line 401 – "limited number of measurements": please restate the exact number.
• Line 482 – Is the volcanic plume consistently the highest aerosol layer?
• Lines 597–600 – There appear to be typographical errors in this bibliography item.

Scientific significance: Excellent

The study provides a significant and original contribution. The combined use of IAC-IGN video-based height retrievals, ACTRIS–AEMET ground lidars, and satellite products provides a comprehensive dataset unprecedented for the 2021 Tajogaite eruption. The documented influence of plume height on SO₂ mass estimation, with up to an 85% reduction in bias upon correction, holds considerable operational and scientifically significant.

Scientific quality. Excellent

The methodology is rigorous and thoroughly described. The analysis employs independent instruments and cross-validation techniques, thereby ensuring robustness. The primary limitation lies in the absence of detailed uncertainty propagation and supplementary statistical metrics (e.g., RMSE, correlation) between datasets — these are minor issues but prevent achieving an optimal score. The discussion is well-balanced, and references are comprehensive.

Presentation quality: Good

The manuscript exhibits a well-organized structure, with fluent English usage. The figures are informative and visually clear; however, enhancements such as clarification, inclusion of error bars, summary statistics, and a brief note regarding algorithm parameters could be beneficial. These suggestions pertain to minor presentation refinements rather than scientific shortcomings. Additionally, the inclusion of other pertinent references from previous works might have been advantageous.

General Comments:

This manuscript offers a thoroughly conducted and significant investigation into the characterization of plume heights during the 2021 Tajogaite (La Palma) eruption, utilizing complementary datasets from IGN video observations, AEMET–ACTRIS aerosol profilers, and satellite instruments. The study emphasizes the essential role of precise, real-time plume height measurements in ensuring reliable satellite retrievals of volcanic emissions and establishes a valuable framework for future volcanic crisis management.

The primary enhancements required are minor, including the incorporation of fundamental statistical indicators such as RMSE and correlation for the AEMET-IGN comparison (see Fig. 4), a concise sensitivity analysis of CALIOP results, clarification or correction within graphical regions, and the explicit delineation of uncertainty ranges.

The manuscript is clearly written, well organized, and enhanced with high-quality figures. It makes a significant and original contribution to atmospheric measurement science. I recommend acceptance after minor revisions.

Technical Comments:

Regarding Figure 4: This plot would substantially benefit from the inclusion of a descriptive table that provides a comprehensive statistical analysis. This should include correlation coefficients between the AEMET-ACTRIS and IGN datasets for dispersive plume heights (h_d). Additionally, such a table could quantify differences stratified by AEMET instrument type in comparison to IGN measurements, thereby enhancing the interpretability of inter-method consistency. Notably, multiple data points appear for the same day and source (particularly for h_d, IGN), which may introduce visual clutter; consolidating these into daily aggregates—such as means and standard deviations, where applicable—could improve clarity. Nonetheless, the table already presents a synthesized view, as it is effectively summarized in Figure 5a through daily averaged values by source. The proposed statistical table would thus serve as a valuable complement for a rigorous intercomparison.

Regarding Figure 6: The discussion of wind direction analysis in lines 473–479 lacks sufficient clarity, particularly in elucidating the methodological basis for the wind rose construction. Intermediate directional sectors (intercardinal headings) between principal cardinal points (N–E–S–W) are incorrectly labeled; for instance, the sector between south and west should be designated SW, with analogous corrections for other quadrants. The boundary between W and SW, corresponding to 247.5° (referenced to 0° as north) as WSW, exemplifies this issue. Conventionally, wind roses depict the direction from which the wind originates (provenance), rather than toward which it blows. I recommend redrawing the wind rose with explicit labeling of the directional convention (e.g., "wind from" or "wind toward") to avoid ambiguity. Furthermore, while Figure 1 accurately positions the Tazacorte (west) and Fuencaliente (south) stations relative to the island, the text and Figure 6 introduce confusion in their spatial referencing, which should be reconciled for consistency.

Regarding Figure 8 and section 4.4: the data points representing the eruptive column height (h_ec) are indicated by blue circles, not orange as might be inferred from the caption or legend—please verify and rectify this for accuracy. Additionally, the use of the color “red” may be preferable to “light red.” The SO₂ emission rates are expressed in kilotonnes, yet they seem to pertain to daily fluxes (kt day⁻¹); explicitly stating the temporal averaging (e.g., daily emission rates [kt·day⁻¹]) in the axis labels and accompanying text would prevent misinterpretation. Furthermore, it is advisable to review the bibliography to include any prior studies that report similar underestimations of satellite-derived emission rates during volcanic eruptions (e.g., via UV hyperspectral retrievals). If applicable, incorporate references to complementary ground-based or alternative methodological estimates of SO₂ emission rates (kt day⁻¹), such as differential optical absorption spectroscopy (DOAS) or flux tower measurements related to Tajogaite, in order to provide a more comprehensive contextualization of the findings.

I recommend reviewing the figure/table captions alongside their narrative in the text to ensure complete consistency.