Two-year measurements of Black Carbon properties at the high-altitude mountain site of Pic du Midi Observatory in the French Pyrenees

Tinorua, Sarah; Denjean, Cyrielle; Nabat, Pierre; Bourrianne, Thierry; Pont, Véronique; Gheusi, François; Leclerc, Emmanuel

doi:https://doi.org/10.5194/egusphere-2023-570

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https://doi.org/10.5194/egusphere-2023-570

Preprints

11 Apr 2023

| 11 Apr 2023

Two-year measurements of Black Carbon properties at the high-altitude mountain site of Pic du Midi Observatory in the French Pyrenees

Sarah Tinorua, Cyrielle Denjean, Pierre Nabat, Thierry Bourrianne, Véronique Pont, François Gheusi, and Emmanuel Leclerc

Abstract. Black Carbon containing particles (BC) are strong light absorbers, causing substantial radiative heating of the atmosphere. The climate-relevant properties of BC are poorly constrained in high-elevation mountain regions, where numerous complex interactions between BC, radiation, clouds and snow have important climate implications. This study presents two-year measurements of BC microphysical and optical properties at the research station of Pic du Midi (PDM), a high-altitude observatory located at 2877 m above sea level in the French Pyrenees. Among the worldwide existing long-term monitoring sites, PDM has experiences limited influence of the planetary boundary layer (PBL), making it an appropriate site for characterizing free tropospheric (FT) BC. The classification of the dominant aerosol type using the spectral optical properties of the aerosols indicates that BC was the predominant absorption component of aerosols at PDM and controlled the variation of Single Scattering Albedo (SSA) throughout the two years. Single-particle soot photometer (SP2) measurements showed a mean mass concentrations of BC (M_BC) of 35 ng m⁻³ and a relatively constant BC core mass-equivalent diameter of around 180 nm, which are typical values for remote mountain sites. Combining the M_BC with in situ absorption measurements yielded a BC mass absorption coefficient (MAC_BC) of 9.8 ± 2.7 m² g⁻¹ at 880 nm, which corresponds to an absorption enhancement (E_abs) of 2.4 compared to that of bare BC particles with equal BC core size distribution. A significant reduction of the ratio ∆BC / ∆CO when precipitation occurred along the air mass transport suggests wet removal of BC. However we found that the wet removal process did not affect the size of BC, resulting in unchanged E_abs . We observed a large seasonal contrast in BC properties with higher M_BC and E_abs in summer than winter. In winter a strong diurnal variability of MBC (E_abs) with higher (lower) values in the middle of the day was linked to the injection of BC originating from the PBL. During summer in contrast, M_BC showed no diurnal variation was rather constant despite more frequent PBL-conditions, implying that M_BC fluctuations were rather dominated by regional and long-range transport in the FT. A body of evidence suggests that biomass burning emissions effectively altered the concentration and optical properties of BC at PDM, leading to higher E_abs in summer compared to winter. The diurnal pattern of E_abs in summer was opposite to that observed in winter with maximum values of 2.9 observed at noon. We suggest that this daily variation results from photochemical processing driving BC mixing state rather than a change in BC emission source.

Such direct two-year observations of BC properties provide quantitative constraints for both regional and global climate models and have the potential to close the gap between model predicted and observed effects of BC on regional radiation budget and climate. The results demonstrates the complex influence of BC emission sources, transport pathways, atmospheric dynamics and chemical reactivity in driving the light absorption of BC.

Received: 24 Mar 2023 – Discussion started: 11 Apr 2023

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Journal article(s) based on this preprint

08 Feb 2024

Higher absorption enhancement of black carbon in summer shown by 2-year measurements at the high-altitude mountain site of Pic du Midi Observatory in the French Pyrenees

Sarah Tinorua, Cyrielle Denjean, Pierre Nabat, Thierry Bourrianne, Véronique Pont, François Gheusi, and Emmanuel Leclerc

Atmos. Chem. Phys., 24, 1801–1824, https://doi.org/10.5194/acp-24-1801-2024,https://doi.org/10.5194/acp-24-1801-2024, 2024

Short summary

Sarah Tinorua, Cyrielle Denjean, Pierre Nabat, Thierry Bourrianne, Véronique Pont, François Gheusi, and Emmanuel Leclerc

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-570', Anonymous Referee #1, 28 Apr 2023

SUMMARY
The work of Tinorua et al. provides interesting dataset on black carbon properties at a high-mountain site in Europe. These sorts of data are rare and of great interest. The aim of the manuscript is to understand the variability of black carbon properties as function of season, dynamics of the boundary layer and wet removal. Although the current dataset might allow investigating these processes, the presentation and discussion of the results prevents the authors to clearly communicate their message. The language and nomenclature are often problematic to the understanding of the text. Which require a thoughtful revision. Often, the authors jump to conclusions very fast, without a proper description of the observed parameters and with a superficial use of references. As a consequence, the processes leading to the observed changes of rBC properties are often unclear. I suggest the authors to clarify their goals, reduce to a minimum the non-essential discussion and elaborate more in details their hypothesis. I also advise caution when discussing “photochemical processes” and “hygroscopicity”, which cannot be investigated with the current dataset. In its current status, the manuscript is not suitable for publication. However, I invite Tinorua et co-authors to consider the major comments and a multitude of specific, yet not minor, comments for resubmission after major changes.

MAJOR COMMENTS
First, the manuscript would benefit from a deep revision of the language, which often results non-scientific and approximative. The authors are also invited to revise the format of citations, acronyms, and units and the grammar. See specific comments.
Nomenclature is extremely important. The authors should make sure to provide the correct information especially when using abbreviations and acronyms. 1) When dealing with optical properties, it is essential to always declare the wavelength. This is not always done, in the text and especially in the figures. In some cases, it thus results difficult to understand at what wavelengths the measurements are performed. 2)Every soot-measuring technique is based on different properties of the aerosol; hence, instrument specific nomenclature must be used. Soot measured with SP2 should be named rBC (refractory black carbon). Soot measured with filter-based photometers should be named eBC (equivalent black carbon). Soot measured with thermal-optical method should be named EC (elemental carbon). This nomenclature is not applied to the data presented here and to the results of other works. Please revise all the nomenclature and resulting abbreviation following Petzold et al. (2013).
The SP2 offers the possibility to quantify the mixing state (PSD detector and time-lag) and “composition” (colour ratio) of rBC. Unfortunately, these analyses are not performed, although it might help understanding ageing process and absorption enhancement, influence of different sources and potentially wet removal. Could the author explain why mixing-state and colour-ratio were not presented in the manuscript?
The discussion of results and its interpretation is often superficial. This is particularly true in Section 3.1 and 3.2, where a detailed variability of aerosol and BC properties is provided but not discussed with the appropriate literature context. The text reads like a list of numbers followed by a list of references, while the reasons causing the variability is often explained with short and generic sentences like “It has been attributed to the seasonal variation of the continental boundary layer height, long-range transport events (e.g. Saharan dust outbreaks, coal burning from eastern Europe) and biomass burning both from forest fires in summer and domestic heating in winter.” I suggest the author rethinking all the results section to improve their data interpretation and to set clear scientific objectives.
The figures based on time series are not particularly helpful. If the authors aim to discuss the seasonal variability it is advisable to use a longer time stamp (1 month or 2 weeks). In order to provide evidence of correlations between the various properties I also suggest using scatter plots.

SPECIFIC COMMENTS
L30: Merge the two statements, not clear what “this” refers to.
L36-37: please add a reference.
L39-40: the definition is correct, but it is not described how Mac is measured. A short description of the methodology is needed since later on (L43) the instrumental influence is mentioned.
L53: too many references, select the most relevant to deliver your message.
L58: what it is meant with “multiplied by two”?
L66-76: part of this sub-paragraph can be moved into the methodology (ABL-Topoindex). Listing of the sections is not needed. I suggest rewriting the current paragraph focussing on the goals of your work.
L90: replace “sucked” with “sampled”
L94: DMT is not based any longer in Boulder, but in Longmont
L93-113: Although being relatively tedious, nomenclature is important. BC measured via laser-induced incandesce technique is normally referred as rBC (refractory black carbon). I suggest reading Petzold et al. (2013) for more details. Considering this technicality, I also recommend the authors to replace “BC” with “rBC” in the text and in all abbreviations (M_rBC,D_rBC, etc…) when referring to their or other SP2 measurements. BC can be used for more generic discussion in the introduction.
L100: out of curiosity, did the authors ever compared the results obtained with the Python code and the SP2 Toolkit?
L102: I do not see an increase of mass concentration at diameter smaller than 90 nm in Figure S1. Please reformulate or verify the top panel of Figure S1. Figure S1 shows both mass and number size distribution, but only mass is described.
L103: “detection range”, not “detection window”.
L106-113: Please define what “dg” and “σg” mean. Assuming these are the geometric mean and geometric standard deviation, how these were defined, empirically? For mode 1. The SP2 lower size quantification limit was 90 nm. Does it mean that the lognormal fit is applied to the 90-100 nm diameter range to derive mode1?
Figure S1 shows the size distribution of rBC, but on what time scale? With what temporal resolution was the MBC-correction calculated? Would it change during different conditions (PBL, FT, winter, summer, etc…)?
The relative standard deviation of the correction factor is approximately 90%, this lets me thing that non-negligible variability was observed during the measuring period. Could the authors have used a time dependent correction factor instead of constant one for the full dataset?
Considering the temporal variability of MBC-correction, I would like to see how MAC correlate with the correction factor.
L115: please provide the model, manufacturer, company, and country for the TSI instruments, as it is nicely done for the other instruments.
L121: List the measuring wavelengths.
L125: since is not yet published, the Cref value used in the present work should be described a bit better (location of the measurement, reference instrument, wavelength) and compared to previous studies. Since the manuscript is in preparation, and not submitted the year is not relevant.
L126a: I strongly do not recommend the use of “MBC” for the BC mass concentration derived from the aethalometer data. First, the correct nomenclature should be equivalent black carbon (eBC; Petzold et al., 2013). Second, the mass concentration derived from SP2 measurements is also abbreviated as MBC. As a result, it become tremendously confusing to understand how MB is derived in the rest f the paper. Update the use of nomenclature.
L126b: Were the MeBC and σap limits corrected with Cref? At what wavelenght these values were derived, this is particoularly important (especially for σap). If I take 0.0215 Mm−1 and 0.005 μg m−3 I obtaine a MAC (or a mass attenuation coefficient) of 4.3 m2/g, please revise these values. And set the limit of AE33 based on absortion coefficient rather than MeBC, since you have a more reliable instrument (SP2) to measure the mass of rBC.
L130-132: when providing the information about the instruments try do be cosistent with the rest of the paper and provide (model, manufacturer, company, and country), as done for the aerosol instruments
L133 I suggest removing ΔBC/ΔCO in this section, since it comes out of the blue without any context and it is anyway explained later in the text.
L144: The authors should explain clearly that AAE was calculated between 450-635 nm to match the wavelength range of the Nephelometer. Since the measuring wavelengths of the Aethalometer are not listed, it becomes harder for the reader to understand why σap660 was adjusted to 635 nm.
L141-151: I believe a short explanation on what these optical properties represent is needed here. SSA, What SSA, AAE and SAE represent, why they are climatically relevant?
L155-157: I do not agree with the nomenclature choice. If ΔBC/ΔCO is the ratio of MrBC over ΔCO, it should be simply called MrBC/ΔCO, as done by previous studies cited in the result section (Liu et al., 2010; McMeeking et al., 2010).
L160: MBC under (resp. over) 160 the 5th (resp. 95th) percentile? Rephrase.
L161: I suggest giving more explanation about the influence of dust on absorption. Often, the authors do not provide adequate context to very specific statements, assuming that every reader has a deep knowledge of the treated topic.
L167-170. Provide some references for each method.
L171: correct “1,95” in “1.95”. Moreover, I strongly recommend reading Liu et al. (2020), who showed that, despite being widely used, 1.95-0.79i might not be representative of realistic condition. The authors are invited to verify the sensitivity of their calculated MACbare as function of different refractive index. As a matter of fact, Figure S3 showed a maximum MACbare below 5 m2/g which considerably lower than MAC of fresh and bare Bc presented by Bond (7.5m2/g). I imagine that Eabs presented here might be overestimated.
L183-195: for non-expert readers, this subsection might result of difficult understanding. Since the analysis is important, I suggested providing more details on how the ranking is calculated (more technical aspects could go in the supplementary). As it is, FigureS4 does not really help understanding the anabatic ranking, since zero context is provided in the supplementary.
L191: I find the note particularly disturbing. Please avoid statements like “make no sense”. The fluctuation after rank 282 are not negligible and more noisy than in Griffiths et al. (2014). Please try to argue what might be the natural causes leading to the radon fluctuation. Could it be that these values are false negatives? Could the radon ranking be verified as function of water vapour as done in Griffiths et al. (2014)?
L192-195: I am not sure to properly understand this final selection. The periods under the influence of PBL presented later are based on hourly selection and not daily selection (for ranking below 200 in the “anabatic-subset”), right? The opposite was done for FT influence. I expect the PBL-periods to occur preferentially during day-time, while FT-periods during night-time. Is the analysis only considering day-time or it does include also night-time?
L202: m.s−1. Remove the dot.
L223-230: SSA at what wavelength? In figure 4a there are values well below 0.93. Is a monthly minimum, a season minimum? Please explain better. The simultaneous increase of SAE and absorption does not automatically indicate that absorbing particles are small in size. It must be kept in mind that BC is co-emitted with other fine aerosol species such as sulfate. I fund however interesting that the maximum peak of absorption does not correspond with a minimum of SSA. The reasons beyond the seasonal variability are actually not explained (“It has been attributed to the seasonal variation of the continental boundary layer height, long-range transport events and biomass burning both from forest fires in summer and domestic heating in winter.” is a very generic statement).
L259: check reference format
L260: why “MBCs”?
L260: Jungfraujoch name.
L260-265: The seasonal variability of BC mass and absorption is opposite to background and polluted stations, where higher values are observed during winter compared to summer (among others: Yttri et al., 2007; Zanatta et al., 2016). The authors should explain this difference and potentially exploit it to introduce the analysis performed in the following sections of their works.
L268: “Seasonal differences between the origin of highest MBC are thrown into relief,”…not sure what it is meant here.
L273: discussion discussed. Avoid repetitions.
L268-272: From my point of view, Figure 7 shows that 1) the wind patterns are similar in winter and summer; 2) high MBC are associated with low wind speed; 3) and that there is a north scarred signal in winter and southern signal in summer. With the MBC scale and so many points, I cannot identify any clear correlation between wind direction and BC concentration, so I do not agree with the statement “highlighting different BC geographical sources” Similar reasoning can be done for Figure S5, where the overall origin of the air masses lays in the same western sector in both seasons. To improve the visualisation and interpretation of the data, I suggest organizing the wind direction in broader classes (10-20 degrees) and normalize the MBc to its maximum. This modification might help identify a correlation between wind direction and BC concentration
L270: please define summer and winter, this applies elsewhere in the text.
L275-285: So, what it is the conclusion of this analysis?
L320: All paper is based on winter and summer differences. I suggest removing non-essential information like the daily cycle in autumn and spring. Considering that little to no explanation is given about the diurnal-seasonal change, I cannot fully understand the relevance or the aim of this anylsis. As said already, the authors should try to motivate the observed variability, giving context and explanation. Section 3.3 suffers, in its entirety, of this problem.
L325:Section 4 is still part of the results, right? So it should be Section 3.x. Please correct.
L327: As it is shown in the following section, BC mass concentration and BC/CO ratio drastically change (at least in winter) due to anabatic injection from the PBL. Under the influence of PBL injection of fresh BC, wet removal has a smaller impact of BC properties compared to free tropospheric conditions. If the authors excluded periods affected by precipitation in Section 4.2, period under the influence of PBL should be excluded here. This additional filter will reduce the number of atmospheric variable and, perhaps, improve the interpretation of the results.
L356: biomass burning influence. rBC emitted by different sources might show a difference in properties. If the biomass plumes were fresh, the authors should be able to see a difference in the size distribution, and, potentially, in the colour-ratio (ratio of BB over NB channel of the SP2).
L357: Be consistent with cross-references…heather is “Fig.X” or “Figure X”
L362: this is most likely due to the lower concentration of BC observed in the PBL in the summer period.
L348-390: why the size distribution of rBC is not shown here? It might help with the data interpretation.
L369: what is “this evidence”. Reduce the use of “this”, it makes difficult to understand what the authors refer to.
L371: IAGOS…Always explain every abbreviation
L375-379: long unclear sentence, rephrase.
L384-390: Are the SMPS data filtered for FT and PBL conditions? Please specify. If this is not the case, PBL aerosol injection might potentially explain the concentration increase of smaller particles (PBL influence timing is exactly the same FigureS8). Overall, the statement is mostly speculative since the authors cannot prove the occurrence of coagulation and condensation on rBC cores. I thus would not call it “evidence” but rather “hypothesis”. Moreover, the SP2 is capable of providing coating thickness (via the position sensitive detector) and a simpler proxy for mixing-degree (scattering- incandescence time lag). Could the authors explain why these two analyses were not applied?
L399-403: In the present work no evidence is provided on interaction with snow, coating thickness, lifetime, condensation rate or gaseous precursors. Only results obtained by the present study should be discussed in the conclusion section. This part is mostly speculative and I suggest removing it.
L405: I would like to see if these results might change by removing the PBL periods.
L406-407: avoid the use of references in the conclusions. Especially 4 in a row.
L415: What is the “evidence” exactly. Please elaborate.
L423-427: ageing time scale and its impact on cloud activation and optical properties of BC is not treated in the present work. Saying that wet removal is independent from size and mixing state, and that hygroscopicity is not treated properly in models is a bold statement…I recommend caution. Same goes for the following statement.
F1: This figure might benefit some editing. Besides the low resolution, I suggest removing the picture (although beautiful) and introduce a double map with a continental and regional scale. More info could be provided within the figure such as coordinates, altitude, managing institute, ACTRIS name, station type (mountain, background…), instrument list…
F2: I do not think that Figure 2 is needed. The text in section 3.1 describes well enough the general meteorological conditions. Since day-by-day variability is not discussed (and there is no need), I suggest removing the full figure
F6: Figure 6, as Figure 2 and 4, suffers from the choice of using a daily temporal resolution. Since the authors are mostly discussing the seasonal variability, a longer time scale (month) will help visualizing the seasonal changes.
F10b-e: axis is Eabs, caption is MACbc, correct.
FS6: I suggest plotting this graph with daily or weekly temporal resolution.
FS9 Shouldn’t the points have the same colour in the top and bottom panels?
FS10: usually nucleation mode is defined as D<10 nm

REFERENCES
Griffiths, A. D., Conen, F., Weingartner, E., Zimmermann, L., Chambers, S. D., Williams, A. G., and Steinbacher, M.: Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch, Atmospheric Chem. Phys., 14, 12763–12779, https://doi.org/10.5194/acp-14-12763-2014, 2014.
Liu, D., Flynn, M., Gysel, M., Targino, A., Crawford, I., Bower, K., Choularton, T., Jurányi, Z., Steinbacher, M., Hüglin, C., Curtius, J., Kampus, M., Petzold, A., Weingartner, E., Baltensperger, U., and Coe, H.: Single particle characterization of black carbon aerosols at a tropospheric alpine site in Switzerland, Atmos Chem Phys, 10, 7389–7407, https://doi.org/10.5194/acp-10-7389-2010, 2010.
Liu, F., Yon, J., Fuentes, A., Lobo, P., Smallwood, G. J., and Corbin, J. C.: Review of recent literature on the light absorption properties of black carbon: Refractive index, mass absorption cross section, and absorption function, Aerosol Sci. Technol., 54, 33–51, https://doi.org/10.1080/02786826.2019.1676878, 2020.
McMeeking, G. R., Hamburger, T., Liu, D., Flynn, M., Morgan, W. T., Northway, M., Highwood, E. J., Krejci, R., Allan, J. D., Minikin, A., and Coe, H.: Black carbon measurements in the boundary layer over western and northern Europe, Atmos Chem Phys, 10, 9393–9414, https://doi.org/10.5194/acp-10-9393-2010, 2010.
Petzold, A., Ogren, J. A., Fiebig, M., Laj, P., Li, S.-M., Baltensperger, U., Holzer-Popp, T., Kinne, S., Pappalardo, G., Sugimoto, N., Wehrli, C., Wiedensohler, A., and Zhang, X.-Y.: Recommendations for reporting “black carbon” measurements, Atmos Chem Phys, 13, 8365–8379, https://doi.org/10.5194/acp-13-8365-2013, 2013.
Yttri, K. E., Aas, W., Bjerke, A., Cape, J. N., Cavalli, F., Ceburnis, D., Dye, C., Emblico, L., Facchini, M. C., Forster, C., Hanssen, J. E., Hansson, H. C., Jennings, S. G., Maenhaut, W., Putaud, J. P., and Tørseth, K.: Elemental and organic carbon in PM10: a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP, Atmos Chem Phys, 7, 5711–5725, https://doi.org/10.5194/acp-7-5711-2007, 2007.
Zanatta, M., Gysel, M., Bukowiecki, N., Müller, T., Weingartner, E., Areskoug, H., Fiebig, M., Yttri, K. E., Mihalopoulos, N., Kouvarakis, G., Beddows, D., Harrison, R. M., Cavalli, F., Putaud, J. P., Spindler, G., Wiedensohler, A., Alastuey, A., Pandolfi, M., Sellegri, K., Swietlicki, E., Jaffrezo, J. L., Baltensperger, U., and Laj, P.: A European aerosol phenomenology-5: Climatology of black carbon optical properties at 9 regional background sites across Europe, Atmos. Environ., 145, 346–364, https://doi.org/10.1016/j.atmosenv.2016.09.035, 2016.

Citation: https://doi.org/10.5194/egusphere-2023-570-RC1
- AC3:
  'Reply on RC1', Sarah Tinorua, 19 Jul 2023
  
  The response to the Reviewer #1 can be found in the attached file
  
  Citation: https://doi.org/10.5194/egusphere-2023-570-AC3
  - AC4: 'Reply on AC3', Sarah Tinorua, 20 Jul 2023
    
    The previous answer contained an error. Please find attached the corrected answers to the reviewer's comment #3
    
    Citation: https://doi.org/10.5194/egusphere-2023-570-AC4
  - AC6: 'Reply on AC3', Sarah Tinorua, 20 Jul 2023
    
    The previous answer contained an error. Please find attached the corrected answers to the reviewer's comment #1
    
    Citation: https://doi.org/10.5194/egusphere-2023-570-AC6
RC2:
'Comment on egusphere-2023-570', Anonymous Referee #2, 04 May 2023
This study conducted two-year measurements of black carbon properties at a mountain site in the French Pyrenees to investigate BC microphysical and optical properties at high altitude and characterize BC in both PBL and FT. The study reported detailed BC mass concentration, BC mass absorption coefficient, Single Scattering Albedo, and absorption enhancement in different seasons, while ΔBC/ΔCO was introduced to quantify the emission and wet scavenging of BC. Generally, this paper is well-organized and informative, providing vital information on climate-relevant properties of BC at high altitude while aiding in constraints for climate models. However, before acceptance of this paper, the following issues need to be resolved:

Instrumentation: In Sec. 2.2.1, the air was heated to keep the samplings dry. Could this measure alter the properties of BC, e.g., leading to some mass loss of volatile substances in the coating materials of BC particles?

It will be also useful to examine the coated size of BC measured by the SP2 for the discussion about the mixing state of BC.

Eq. (1) and Eq. (2) are wrong, it should be log (450/635) instead of log(450)/log(635).

Line 276: Based on your results, what can be the main influence that caused a higher ΔBC/ΔCO in summer than in winter when considering the larger amount of precipitation in summertime?

Line 313-314: “It is expected that the BC particles reaching PDM would be aged and relatively thickly coated.” some evidence is needed here, a previous study which also conducted experiments on a mountain site influenced by the PBL intrusion (doi: 10.5194/acp-19-6749-2019) may support your results.

The authors use “the size of BC core sampled at PDM was higher than other studies” to explain “BC wet scavenging did not significantly affect the size of BC-containing particles,” which is not convincing. A previous study performed on a mountain site during wintertime in Beijing reported larger BC core than the present study but showed significantly lowered BC core size after wet scavenging due to larger BC cores were preferentially wet removed (doi: 10.1029/2019GL083171). Please give more explanations.

The wet scavenging process of BC due to PBL cloud during its vertical transport within PBL around midday may partly explain the relationship between the diurnal variation of Eabs and ΔBC/ΔCO in summer (doi: 10.1029/2020JD033096)

Minor:
Line 171: “1,95 should be 1.95”

Line 173: what do you mean by “artifacts”

BL and PBL need to be uniform.

Abstract, line 18: This sentence was confusing.
Citation: https://doi.org/10.5194/egusphere-2023-570-RC2
- AC1: 'Reply on RC2', Sarah Tinorua, 19 Jul 2023
  
  The response to the Reviewer #2 can be found in the attached file
  
  Citation: https://doi.org/10.5194/egusphere-2023-570-AC1
RC3:
'Comment on egusphere-2023-570', Anonymous Referee #3, 10 May 2023

Major comments
Tinorua et al. provides a description of an important black carbon data set collected at a high-altitude mountain site in France – these sorts of data sets and measurements are indeed essential to improving climate models. However, the impact of this data set is not compellingly described in the manuscript – there are some sections bogged down in numbers and lists, some paragraphs that making sweeping general statements without the rigorous analysis / discussion that I would expect of an ACP paper, and perhaps most importantly, the implications of the findings on climate models (as described in the article introduction) are limited to a brief 6-line paragraph at the end of the manuscript.
These problems of narrative, hypothesis generation and testing, and rigor can even be seen in the title, which is overly generic – I would like to see the authors more precisely focus and describe their key findings and make sure these findings are well supported in the paper, clear in the title and that the methods are described in more detail. In summary, I think the manuscript has a lot of potential after major revisions to sharpen the focus. I look forward to this paper being published in ACP after making these adjustments.
There are also some grammatical / style issues throughout that would benefit from an additional proofread, and the time series figures spanning the full 2-year campaign are generally overwhelming. I would recommend that some of these figures be moved to the SI and that focused vignettes of the data be presented in the main manuscript. Additionally, the Supporting Information lacks a lot of detail and description; it is simply a collection of figures, which limits its utility.
Specific Comments
Title: I recommend making the title more descriptive of the findings. It’s too generic as written.
Line 54: Can you define what is meant by “short periods” – currently subjective
Figure 1: Map resolution is poor – can you make this clearer?
Lines 89-91: I would like to see a bit more description of the inlet and its design – what is the total flow rate and diameter? What are the particle losses? If there is a citation that describes this inlet in more detail perhaps it could be provided.
Line 101-102: The process of developing the size distributions shown in Figure S1 in the Supplement are not described – I don’t see any descriptive text in the SI, either. Can you provide some more detail in the SI? Feel like there is a big jump here. How are you measuring size distribution? How do you know that all of the ultrafine particles are indeed BC? I think I am just missing a few steps here because I don’t have the relevant expertise / background.
Section 2.2.3: I see now that you are describing the SMPS in the 10-1000 nm size range – would recommend re-ordering the manuscript so you aren’t introducing results before you have mentioned the methods. My question on how you know the size distribution below 90 nm is BC still stands.
Lines 124-126: I do not believe these in preparation materials were provided for review – can you provide more details on the calculation of the C value in the response to reviewers?
Section 2.3: I find the description of the equations (1-3) to be confusing to follow. You mention on line 143 the calculation of the aerosol absorption coefficient at 635 nm using another AAE calculation but the justification for this approach seems to be missing. I believe this is linked to the nephelometer wavelength ranges but its difficult to follow the narrative.
Line 161: You are citing material that to my knowledge is not available for review – please provide details even if it is confidentially to reviewers only. I would like to see some of these details from the in preparation manuscript if possible.
Lines 167-171: I find the justification of choice for MAC_bare to be lacking – what are the implications of your choice? Is this still standard practice given that you are citing a paper from 2006? Given the interest in the subject matter I require more convincing that this is the appropriate method.
Figure 2: I’m not sure this figure has a lot of value in the main manuscript given that you have already described the findings in the text in Section 3.1. I would rather see this figure in the SI and instead have you provide more details on the methods section, which I found to be lacking.
Figure 4: The time series are difficult to follow because you are plotting the full two years. I am not sure this is the most effective way to communicate this information. Perhaps you can re-arrange to highlight the seasonality you describe in the text and move the full time series to the SI.
Lines 253-254: If this is a key conclusion of the work then this should be better reflected in abstract / title of the paper. Also given that it was unexpected, can you probe more deeply why you think this was observed and provide more detail that you are confident that it isn’t an artifact of your sampling methods or calculations? Would just like to see this better and more specifically justified.
Lines 297-298: I feel like you could be more precise describing how different techniques and correction factors influence the differences. This feels overly generalized as written. Additionally, if you have confidence in your very high MAC value, then what are the implications of this?
Figure 7: You should have a consistent scale for panels (a) and (b).
Line 320: Please avoid sensational language like “remarkable”. Do you mean a notable diurnal profile?
Section 4.1 and wet scavenging: Conclusions about the significance of precipitation I think would benefit from a more rigorous statistical test vs descriptive observations that you have provided. Additionally, this whole section reads as quite speculative. This is important given that this is one of your main conclusions of note.
Lines 348-350: Can you clarify why precipitation events were removed? Because of the influence on the ΔBC/ΔCO ratio? Was slightly unclear to me.
Lines 378-379: Can you describe what these additional measurements would be? And the more precise source apportionment?
Lines 420-427: To me these are the most important lines in the manuscript – the implications of your findings. I am a little disappointed that this is relegated to one brief paragraph and that your major conclusion re: wet scavenging is not as thoroughly assessed in the paper as is likely warranted given the conclusion. I would like to see the implications section for climate models more rigorously discussed.

Citation: https://doi.org/10.5194/egusphere-2023-570-RC3
- AC2:
  'Reply on RC3', Sarah Tinorua, 19 Jul 2023
  
  The response to the Reviewer #3 can be found in the attached file
  
  Citation: https://doi.org/10.5194/egusphere-2023-570-AC2
  - AC5: 'Reply on AC2', Sarah Tinorua, 20 Jul 2023
    
    The previous answer contained an error. Please find attached the corrected answers to the reviewer's comment #3
    
    Citation: https://doi.org/10.5194/egusphere-2023-570-AC5

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-570', Anonymous Referee #1, 28 Apr 2023

SUMMARY
The work of Tinorua et al. provides interesting dataset on black carbon properties at a high-mountain site in Europe. These sorts of data are rare and of great interest. The aim of the manuscript is to understand the variability of black carbon properties as function of season, dynamics of the boundary layer and wet removal. Although the current dataset might allow investigating these processes, the presentation and discussion of the results prevents the authors to clearly communicate their message. The language and nomenclature are often problematic to the understanding of the text. Which require a thoughtful revision. Often, the authors jump to conclusions very fast, without a proper description of the observed parameters and with a superficial use of references. As a consequence, the processes leading to the observed changes of rBC properties are often unclear. I suggest the authors to clarify their goals, reduce to a minimum the non-essential discussion and elaborate more in details their hypothesis. I also advise caution when discussing “photochemical processes” and “hygroscopicity”, which cannot be investigated with the current dataset. In its current status, the manuscript is not suitable for publication. However, I invite Tinorua et co-authors to consider the major comments and a multitude of specific, yet not minor, comments for resubmission after major changes.

MAJOR COMMENTS
First, the manuscript would benefit from a deep revision of the language, which often results non-scientific and approximative. The authors are also invited to revise the format of citations, acronyms, and units and the grammar. See specific comments.
Nomenclature is extremely important. The authors should make sure to provide the correct information especially when using abbreviations and acronyms. 1) When dealing with optical properties, it is essential to always declare the wavelength. This is not always done, in the text and especially in the figures. In some cases, it thus results difficult to understand at what wavelengths the measurements are performed. 2)Every soot-measuring technique is based on different properties of the aerosol; hence, instrument specific nomenclature must be used. Soot measured with SP2 should be named rBC (refractory black carbon). Soot measured with filter-based photometers should be named eBC (equivalent black carbon). Soot measured with thermal-optical method should be named EC (elemental carbon). This nomenclature is not applied to the data presented here and to the results of other works. Please revise all the nomenclature and resulting abbreviation following Petzold et al. (2013).
The SP2 offers the possibility to quantify the mixing state (PSD detector and time-lag) and “composition” (colour ratio) of rBC. Unfortunately, these analyses are not performed, although it might help understanding ageing process and absorption enhancement, influence of different sources and potentially wet removal. Could the author explain why mixing-state and colour-ratio were not presented in the manuscript?
The discussion of results and its interpretation is often superficial. This is particularly true in Section 3.1 and 3.2, where a detailed variability of aerosol and BC properties is provided but not discussed with the appropriate literature context. The text reads like a list of numbers followed by a list of references, while the reasons causing the variability is often explained with short and generic sentences like “It has been attributed to the seasonal variation of the continental boundary layer height, long-range transport events (e.g. Saharan dust outbreaks, coal burning from eastern Europe) and biomass burning both from forest fires in summer and domestic heating in winter.” I suggest the author rethinking all the results section to improve their data interpretation and to set clear scientific objectives.
The figures based on time series are not particularly helpful. If the authors aim to discuss the seasonal variability it is advisable to use a longer time stamp (1 month or 2 weeks). In order to provide evidence of correlations between the various properties I also suggest using scatter plots.

SPECIFIC COMMENTS
L30: Merge the two statements, not clear what “this” refers to.
L36-37: please add a reference.
L39-40: the definition is correct, but it is not described how Mac is measured. A short description of the methodology is needed since later on (L43) the instrumental influence is mentioned.
L53: too many references, select the most relevant to deliver your message.
L58: what it is meant with “multiplied by two”?
L66-76: part of this sub-paragraph can be moved into the methodology (ABL-Topoindex). Listing of the sections is not needed. I suggest rewriting the current paragraph focussing on the goals of your work.
L90: replace “sucked” with “sampled”
L94: DMT is not based any longer in Boulder, but in Longmont
L93-113: Although being relatively tedious, nomenclature is important. BC measured via laser-induced incandesce technique is normally referred as rBC (refractory black carbon). I suggest reading Petzold et al. (2013) for more details. Considering this technicality, I also recommend the authors to replace “BC” with “rBC” in the text and in all abbreviations (M_rBC,D_rBC, etc…) when referring to their or other SP2 measurements. BC can be used for more generic discussion in the introduction.
L100: out of curiosity, did the authors ever compared the results obtained with the Python code and the SP2 Toolkit?
L102: I do not see an increase of mass concentration at diameter smaller than 90 nm in Figure S1. Please reformulate or verify the top panel of Figure S1. Figure S1 shows both mass and number size distribution, but only mass is described.
L103: “detection range”, not “detection window”.
L106-113: Please define what “dg” and “σg” mean. Assuming these are the geometric mean and geometric standard deviation, how these were defined, empirically? For mode 1. The SP2 lower size quantification limit was 90 nm. Does it mean that the lognormal fit is applied to the 90-100 nm diameter range to derive mode1?
Figure S1 shows the size distribution of rBC, but on what time scale? With what temporal resolution was the MBC-correction calculated? Would it change during different conditions (PBL, FT, winter, summer, etc…)?
The relative standard deviation of the correction factor is approximately 90%, this lets me thing that non-negligible variability was observed during the measuring period. Could the authors have used a time dependent correction factor instead of constant one for the full dataset?
Considering the temporal variability of MBC-correction, I would like to see how MAC correlate with the correction factor.
L115: please provide the model, manufacturer, company, and country for the TSI instruments, as it is nicely done for the other instruments.
L121: List the measuring wavelengths.
L125: since is not yet published, the Cref value used in the present work should be described a bit better (location of the measurement, reference instrument, wavelength) and compared to previous studies. Since the manuscript is in preparation, and not submitted the year is not relevant.
L126a: I strongly do not recommend the use of “MBC” for the BC mass concentration derived from the aethalometer data. First, the correct nomenclature should be equivalent black carbon (eBC; Petzold et al., 2013). Second, the mass concentration derived from SP2 measurements is also abbreviated as MBC. As a result, it become tremendously confusing to understand how MB is derived in the rest f the paper. Update the use of nomenclature.
L126b: Were the MeBC and σap limits corrected with Cref? At what wavelenght these values were derived, this is particoularly important (especially for σap). If I take 0.0215 Mm−1 and 0.005 μg m−3 I obtaine a MAC (or a mass attenuation coefficient) of 4.3 m2/g, please revise these values. And set the limit of AE33 based on absortion coefficient rather than MeBC, since you have a more reliable instrument (SP2) to measure the mass of rBC.
L130-132: when providing the information about the instruments try do be cosistent with the rest of the paper and provide (model, manufacturer, company, and country), as done for the aerosol instruments
L133 I suggest removing ΔBC/ΔCO in this section, since it comes out of the blue without any context and it is anyway explained later in the text.
L144: The authors should explain clearly that AAE was calculated between 450-635 nm to match the wavelength range of the Nephelometer. Since the measuring wavelengths of the Aethalometer are not listed, it becomes harder for the reader to understand why σap660 was adjusted to 635 nm.
L141-151: I believe a short explanation on what these optical properties represent is needed here. SSA, What SSA, AAE and SAE represent, why they are climatically relevant?
L155-157: I do not agree with the nomenclature choice. If ΔBC/ΔCO is the ratio of MrBC over ΔCO, it should be simply called MrBC/ΔCO, as done by previous studies cited in the result section (Liu et al., 2010; McMeeking et al., 2010).
L160: MBC under (resp. over) 160 the 5th (resp. 95th) percentile? Rephrase.
L161: I suggest giving more explanation about the influence of dust on absorption. Often, the authors do not provide adequate context to very specific statements, assuming that every reader has a deep knowledge of the treated topic.
L167-170. Provide some references for each method.
L171: correct “1,95” in “1.95”. Moreover, I strongly recommend reading Liu et al. (2020), who showed that, despite being widely used, 1.95-0.79i might not be representative of realistic condition. The authors are invited to verify the sensitivity of their calculated MACbare as function of different refractive index. As a matter of fact, Figure S3 showed a maximum MACbare below 5 m2/g which considerably lower than MAC of fresh and bare Bc presented by Bond (7.5m2/g). I imagine that Eabs presented here might be overestimated.
L183-195: for non-expert readers, this subsection might result of difficult understanding. Since the analysis is important, I suggested providing more details on how the ranking is calculated (more technical aspects could go in the supplementary). As it is, FigureS4 does not really help understanding the anabatic ranking, since zero context is provided in the supplementary.
L191: I find the note particularly disturbing. Please avoid statements like “make no sense”. The fluctuation after rank 282 are not negligible and more noisy than in Griffiths et al. (2014). Please try to argue what might be the natural causes leading to the radon fluctuation. Could it be that these values are false negatives? Could the radon ranking be verified as function of water vapour as done in Griffiths et al. (2014)?
L192-195: I am not sure to properly understand this final selection. The periods under the influence of PBL presented later are based on hourly selection and not daily selection (for ranking below 200 in the “anabatic-subset”), right? The opposite was done for FT influence. I expect the PBL-periods to occur preferentially during day-time, while FT-periods during night-time. Is the analysis only considering day-time or it does include also night-time?
L202: m.s−1. Remove the dot.
L223-230: SSA at what wavelength? In figure 4a there are values well below 0.93. Is a monthly minimum, a season minimum? Please explain better. The simultaneous increase of SAE and absorption does not automatically indicate that absorbing particles are small in size. It must be kept in mind that BC is co-emitted with other fine aerosol species such as sulfate. I fund however interesting that the maximum peak of absorption does not correspond with a minimum of SSA. The reasons beyond the seasonal variability are actually not explained (“It has been attributed to the seasonal variation of the continental boundary layer height, long-range transport events and biomass burning both from forest fires in summer and domestic heating in winter.” is a very generic statement).
L259: check reference format
L260: why “MBCs”?
L260: Jungfraujoch name.
L260-265: The seasonal variability of BC mass and absorption is opposite to background and polluted stations, where higher values are observed during winter compared to summer (among others: Yttri et al., 2007; Zanatta et al., 2016). The authors should explain this difference and potentially exploit it to introduce the analysis performed in the following sections of their works.
L268: “Seasonal differences between the origin of highest MBC are thrown into relief,”…not sure what it is meant here.
L273: discussion discussed. Avoid repetitions.
L268-272: From my point of view, Figure 7 shows that 1) the wind patterns are similar in winter and summer; 2) high MBC are associated with low wind speed; 3) and that there is a north scarred signal in winter and southern signal in summer. With the MBC scale and so many points, I cannot identify any clear correlation between wind direction and BC concentration, so I do not agree with the statement “highlighting different BC geographical sources” Similar reasoning can be done for Figure S5, where the overall origin of the air masses lays in the same western sector in both seasons. To improve the visualisation and interpretation of the data, I suggest organizing the wind direction in broader classes (10-20 degrees) and normalize the MBc to its maximum. This modification might help identify a correlation between wind direction and BC concentration
L270: please define summer and winter, this applies elsewhere in the text.
L275-285: So, what it is the conclusion of this analysis?
L320: All paper is based on winter and summer differences. I suggest removing non-essential information like the daily cycle in autumn and spring. Considering that little to no explanation is given about the diurnal-seasonal change, I cannot fully understand the relevance or the aim of this anylsis. As said already, the authors should try to motivate the observed variability, giving context and explanation. Section 3.3 suffers, in its entirety, of this problem.
L325:Section 4 is still part of the results, right? So it should be Section 3.x. Please correct.
L327: As it is shown in the following section, BC mass concentration and BC/CO ratio drastically change (at least in winter) due to anabatic injection from the PBL. Under the influence of PBL injection of fresh BC, wet removal has a smaller impact of BC properties compared to free tropospheric conditions. If the authors excluded periods affected by precipitation in Section 4.2, period under the influence of PBL should be excluded here. This additional filter will reduce the number of atmospheric variable and, perhaps, improve the interpretation of the results.
L356: biomass burning influence. rBC emitted by different sources might show a difference in properties. If the biomass plumes were fresh, the authors should be able to see a difference in the size distribution, and, potentially, in the colour-ratio (ratio of BB over NB channel of the SP2).
L357: Be consistent with cross-references…heather is “Fig.X” or “Figure X”
L362: this is most likely due to the lower concentration of BC observed in the PBL in the summer period.
L348-390: why the size distribution of rBC is not shown here? It might help with the data interpretation.
L369: what is “this evidence”. Reduce the use of “this”, it makes difficult to understand what the authors refer to.
L371: IAGOS…Always explain every abbreviation
L375-379: long unclear sentence, rephrase.
L384-390: Are the SMPS data filtered for FT and PBL conditions? Please specify. If this is not the case, PBL aerosol injection might potentially explain the concentration increase of smaller particles (PBL influence timing is exactly the same FigureS8). Overall, the statement is mostly speculative since the authors cannot prove the occurrence of coagulation and condensation on rBC cores. I thus would not call it “evidence” but rather “hypothesis”. Moreover, the SP2 is capable of providing coating thickness (via the position sensitive detector) and a simpler proxy for mixing-degree (scattering- incandescence time lag). Could the authors explain why these two analyses were not applied?
L399-403: In the present work no evidence is provided on interaction with snow, coating thickness, lifetime, condensation rate or gaseous precursors. Only results obtained by the present study should be discussed in the conclusion section. This part is mostly speculative and I suggest removing it.
L405: I would like to see if these results might change by removing the PBL periods.
L406-407: avoid the use of references in the conclusions. Especially 4 in a row.
L415: What is the “evidence” exactly. Please elaborate.
L423-427: ageing time scale and its impact on cloud activation and optical properties of BC is not treated in the present work. Saying that wet removal is independent from size and mixing state, and that hygroscopicity is not treated properly in models is a bold statement…I recommend caution. Same goes for the following statement.
F1: This figure might benefit some editing. Besides the low resolution, I suggest removing the picture (although beautiful) and introduce a double map with a continental and regional scale. More info could be provided within the figure such as coordinates, altitude, managing institute, ACTRIS name, station type (mountain, background…), instrument list…
F2: I do not think that Figure 2 is needed. The text in section 3.1 describes well enough the general meteorological conditions. Since day-by-day variability is not discussed (and there is no need), I suggest removing the full figure
F6: Figure 6, as Figure 2 and 4, suffers from the choice of using a daily temporal resolution. Since the authors are mostly discussing the seasonal variability, a longer time scale (month) will help visualizing the seasonal changes.
F10b-e: axis is Eabs, caption is MACbc, correct.
FS6: I suggest plotting this graph with daily or weekly temporal resolution.
FS9 Shouldn’t the points have the same colour in the top and bottom panels?
FS10: usually nucleation mode is defined as D<10 nm

REFERENCES
Griffiths, A. D., Conen, F., Weingartner, E., Zimmermann, L., Chambers, S. D., Williams, A. G., and Steinbacher, M.: Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch, Atmospheric Chem. Phys., 14, 12763–12779, https://doi.org/10.5194/acp-14-12763-2014, 2014.
Liu, D., Flynn, M., Gysel, M., Targino, A., Crawford, I., Bower, K., Choularton, T., Jurányi, Z., Steinbacher, M., Hüglin, C., Curtius, J., Kampus, M., Petzold, A., Weingartner, E., Baltensperger, U., and Coe, H.: Single particle characterization of black carbon aerosols at a tropospheric alpine site in Switzerland, Atmos Chem Phys, 10, 7389–7407, https://doi.org/10.5194/acp-10-7389-2010, 2010.
Liu, F., Yon, J., Fuentes, A., Lobo, P., Smallwood, G. J., and Corbin, J. C.: Review of recent literature on the light absorption properties of black carbon: Refractive index, mass absorption cross section, and absorption function, Aerosol Sci. Technol., 54, 33–51, https://doi.org/10.1080/02786826.2019.1676878, 2020.
McMeeking, G. R., Hamburger, T., Liu, D., Flynn, M., Morgan, W. T., Northway, M., Highwood, E. J., Krejci, R., Allan, J. D., Minikin, A., and Coe, H.: Black carbon measurements in the boundary layer over western and northern Europe, Atmos Chem Phys, 10, 9393–9414, https://doi.org/10.5194/acp-10-9393-2010, 2010.
Petzold, A., Ogren, J. A., Fiebig, M., Laj, P., Li, S.-M., Baltensperger, U., Holzer-Popp, T., Kinne, S., Pappalardo, G., Sugimoto, N., Wehrli, C., Wiedensohler, A., and Zhang, X.-Y.: Recommendations for reporting “black carbon” measurements, Atmos Chem Phys, 13, 8365–8379, https://doi.org/10.5194/acp-13-8365-2013, 2013.
Yttri, K. E., Aas, W., Bjerke, A., Cape, J. N., Cavalli, F., Ceburnis, D., Dye, C., Emblico, L., Facchini, M. C., Forster, C., Hanssen, J. E., Hansson, H. C., Jennings, S. G., Maenhaut, W., Putaud, J. P., and Tørseth, K.: Elemental and organic carbon in PM10: a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP, Atmos Chem Phys, 7, 5711–5725, https://doi.org/10.5194/acp-7-5711-2007, 2007.
Zanatta, M., Gysel, M., Bukowiecki, N., Müller, T., Weingartner, E., Areskoug, H., Fiebig, M., Yttri, K. E., Mihalopoulos, N., Kouvarakis, G., Beddows, D., Harrison, R. M., Cavalli, F., Putaud, J. P., Spindler, G., Wiedensohler, A., Alastuey, A., Pandolfi, M., Sellegri, K., Swietlicki, E., Jaffrezo, J. L., Baltensperger, U., and Laj, P.: A European aerosol phenomenology-5: Climatology of black carbon optical properties at 9 regional background sites across Europe, Atmos. Environ., 145, 346–364, https://doi.org/10.1016/j.atmosenv.2016.09.035, 2016.

Citation: https://doi.org/10.5194/egusphere-2023-570-RC1
- AC3:
  'Reply on RC1', Sarah Tinorua, 19 Jul 2023
  
  The response to the Reviewer #1 can be found in the attached file
  
  Citation: https://doi.org/10.5194/egusphere-2023-570-AC3
  - AC4: 'Reply on AC3', Sarah Tinorua, 20 Jul 2023
    
    The previous answer contained an error. Please find attached the corrected answers to the reviewer's comment #3
    
    Citation: https://doi.org/10.5194/egusphere-2023-570-AC4
  - AC6: 'Reply on AC3', Sarah Tinorua, 20 Jul 2023
    
    The previous answer contained an error. Please find attached the corrected answers to the reviewer's comment #1
    
    Citation: https://doi.org/10.5194/egusphere-2023-570-AC6
RC2:
'Comment on egusphere-2023-570', Anonymous Referee #2, 04 May 2023
This study conducted two-year measurements of black carbon properties at a mountain site in the French Pyrenees to investigate BC microphysical and optical properties at high altitude and characterize BC in both PBL and FT. The study reported detailed BC mass concentration, BC mass absorption coefficient, Single Scattering Albedo, and absorption enhancement in different seasons, while ΔBC/ΔCO was introduced to quantify the emission and wet scavenging of BC. Generally, this paper is well-organized and informative, providing vital information on climate-relevant properties of BC at high altitude while aiding in constraints for climate models. However, before acceptance of this paper, the following issues need to be resolved:

Instrumentation: In Sec. 2.2.1, the air was heated to keep the samplings dry. Could this measure alter the properties of BC, e.g., leading to some mass loss of volatile substances in the coating materials of BC particles?

It will be also useful to examine the coated size of BC measured by the SP2 for the discussion about the mixing state of BC.

Eq. (1) and Eq. (2) are wrong, it should be log (450/635) instead of log(450)/log(635).

Line 276: Based on your results, what can be the main influence that caused a higher ΔBC/ΔCO in summer than in winter when considering the larger amount of precipitation in summertime?

Line 313-314: “It is expected that the BC particles reaching PDM would be aged and relatively thickly coated.” some evidence is needed here, a previous study which also conducted experiments on a mountain site influenced by the PBL intrusion (doi: 10.5194/acp-19-6749-2019) may support your results.

The authors use “the size of BC core sampled at PDM was higher than other studies” to explain “BC wet scavenging did not significantly affect the size of BC-containing particles,” which is not convincing. A previous study performed on a mountain site during wintertime in Beijing reported larger BC core than the present study but showed significantly lowered BC core size after wet scavenging due to larger BC cores were preferentially wet removed (doi: 10.1029/2019GL083171). Please give more explanations.

The wet scavenging process of BC due to PBL cloud during its vertical transport within PBL around midday may partly explain the relationship between the diurnal variation of Eabs and ΔBC/ΔCO in summer (doi: 10.1029/2020JD033096)

Minor:
Line 171: “1,95 should be 1.95”

Line 173: what do you mean by “artifacts”

BL and PBL need to be uniform.

Abstract, line 18: This sentence was confusing.
Citation: https://doi.org/10.5194/egusphere-2023-570-RC2
- AC1: 'Reply on RC2', Sarah Tinorua, 19 Jul 2023
  
  The response to the Reviewer #2 can be found in the attached file
  
  Citation: https://doi.org/10.5194/egusphere-2023-570-AC1
RC3:
'Comment on egusphere-2023-570', Anonymous Referee #3, 10 May 2023

Major comments
Tinorua et al. provides a description of an important black carbon data set collected at a high-altitude mountain site in France – these sorts of data sets and measurements are indeed essential to improving climate models. However, the impact of this data set is not compellingly described in the manuscript – there are some sections bogged down in numbers and lists, some paragraphs that making sweeping general statements without the rigorous analysis / discussion that I would expect of an ACP paper, and perhaps most importantly, the implications of the findings on climate models (as described in the article introduction) are limited to a brief 6-line paragraph at the end of the manuscript.
These problems of narrative, hypothesis generation and testing, and rigor can even be seen in the title, which is overly generic – I would like to see the authors more precisely focus and describe their key findings and make sure these findings are well supported in the paper, clear in the title and that the methods are described in more detail. In summary, I think the manuscript has a lot of potential after major revisions to sharpen the focus. I look forward to this paper being published in ACP after making these adjustments.
There are also some grammatical / style issues throughout that would benefit from an additional proofread, and the time series figures spanning the full 2-year campaign are generally overwhelming. I would recommend that some of these figures be moved to the SI and that focused vignettes of the data be presented in the main manuscript. Additionally, the Supporting Information lacks a lot of detail and description; it is simply a collection of figures, which limits its utility.
Specific Comments
Title: I recommend making the title more descriptive of the findings. It’s too generic as written.
Line 54: Can you define what is meant by “short periods” – currently subjective
Figure 1: Map resolution is poor – can you make this clearer?
Lines 89-91: I would like to see a bit more description of the inlet and its design – what is the total flow rate and diameter? What are the particle losses? If there is a citation that describes this inlet in more detail perhaps it could be provided.
Line 101-102: The process of developing the size distributions shown in Figure S1 in the Supplement are not described – I don’t see any descriptive text in the SI, either. Can you provide some more detail in the SI? Feel like there is a big jump here. How are you measuring size distribution? How do you know that all of the ultrafine particles are indeed BC? I think I am just missing a few steps here because I don’t have the relevant expertise / background.
Section 2.2.3: I see now that you are describing the SMPS in the 10-1000 nm size range – would recommend re-ordering the manuscript so you aren’t introducing results before you have mentioned the methods. My question on how you know the size distribution below 90 nm is BC still stands.
Lines 124-126: I do not believe these in preparation materials were provided for review – can you provide more details on the calculation of the C value in the response to reviewers?
Section 2.3: I find the description of the equations (1-3) to be confusing to follow. You mention on line 143 the calculation of the aerosol absorption coefficient at 635 nm using another AAE calculation but the justification for this approach seems to be missing. I believe this is linked to the nephelometer wavelength ranges but its difficult to follow the narrative.
Line 161: You are citing material that to my knowledge is not available for review – please provide details even if it is confidentially to reviewers only. I would like to see some of these details from the in preparation manuscript if possible.
Lines 167-171: I find the justification of choice for MAC_bare to be lacking – what are the implications of your choice? Is this still standard practice given that you are citing a paper from 2006? Given the interest in the subject matter I require more convincing that this is the appropriate method.
Figure 2: I’m not sure this figure has a lot of value in the main manuscript given that you have already described the findings in the text in Section 3.1. I would rather see this figure in the SI and instead have you provide more details on the methods section, which I found to be lacking.
Figure 4: The time series are difficult to follow because you are plotting the full two years. I am not sure this is the most effective way to communicate this information. Perhaps you can re-arrange to highlight the seasonality you describe in the text and move the full time series to the SI.
Lines 253-254: If this is a key conclusion of the work then this should be better reflected in abstract / title of the paper. Also given that it was unexpected, can you probe more deeply why you think this was observed and provide more detail that you are confident that it isn’t an artifact of your sampling methods or calculations? Would just like to see this better and more specifically justified.
Lines 297-298: I feel like you could be more precise describing how different techniques and correction factors influence the differences. This feels overly generalized as written. Additionally, if you have confidence in your very high MAC value, then what are the implications of this?
Figure 7: You should have a consistent scale for panels (a) and (b).
Line 320: Please avoid sensational language like “remarkable”. Do you mean a notable diurnal profile?
Section 4.1 and wet scavenging: Conclusions about the significance of precipitation I think would benefit from a more rigorous statistical test vs descriptive observations that you have provided. Additionally, this whole section reads as quite speculative. This is important given that this is one of your main conclusions of note.
Lines 348-350: Can you clarify why precipitation events were removed? Because of the influence on the ΔBC/ΔCO ratio? Was slightly unclear to me.
Lines 378-379: Can you describe what these additional measurements would be? And the more precise source apportionment?
Lines 420-427: To me these are the most important lines in the manuscript – the implications of your findings. I am a little disappointed that this is relegated to one brief paragraph and that your major conclusion re: wet scavenging is not as thoroughly assessed in the paper as is likely warranted given the conclusion. I would like to see the implications section for climate models more rigorously discussed.

Citation: https://doi.org/10.5194/egusphere-2023-570-RC3
- AC2:
  'Reply on RC3', Sarah Tinorua, 19 Jul 2023
  
  The response to the Reviewer #3 can be found in the attached file
  
  Citation: https://doi.org/10.5194/egusphere-2023-570-AC2
  - AC5: 'Reply on AC2', Sarah Tinorua, 20 Jul 2023
    
    The previous answer contained an error. Please find attached the corrected answers to the reviewer's comment #3
    
    Citation: https://doi.org/10.5194/egusphere-2023-570-AC5

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Sarah Tinorua on behalf of the Authors (20 Jul 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (27 Jul 2023) by Andreas Petzold

RR by Anonymous Referee #3 (31 Jul 2023)

RR by Anonymous Referee #2 (07 Aug 2023)

RR by Anonymous Referee #1 (09 Aug 2023)

Suggestions for revision or reasons for rejection

REVIEW Preprint egusphere-2023-570

I am glad that Tinorua and co-authors incorporated some of my previous suggestions. In some parts, the manuscript’s quality and readability improved since the first submission. However, this version still suffers from very similar flaws compared to the first draft. The presentation of the results is chaotic since there is little cohesion between the text and the figures. I notice an overall superficiality in justifying technical choices, presenting the data and interpreting the results. Finally, the results are not clearly summarized in the conclusion section, which is a very confusing mix of results, references and speculations. Considering the number of specific comments that can be found as follows (editing, grammar, nomenclature, sequence of figures, etc…), I have the impression that the manuscript was not carefully controlled before resubmission. Despite the high interest in the dataset, I cannot recommend the publication of the manuscript in ACP. I leave the choice of full rejection or resubmission after major changes to the editor, waiting for the pending reviews from other referees.

MAJOR COMMENTS

MULTIPLE SCATTERING CORRECTION
The C value was changed from 3.63 to 3.22 according to Yus-Díez et al. (2021). Considering the importance of this change and the direct effect on absorption coefficient and MAC, the choice should be explained better, and should not be based, solely, on the fact that Montsec d’Ares is a mountaintop site 200 km away from PDM. More specific comments:
- In the main text of Yus-Díez et al. (2021), I could find values between 2.51 and 2.36 for Montsec d’Ares. These values are calculated using a different type of filter and normalized against the MAAP at one single wavelength.
- Finding the value 3.22 in Yus-Diez requires some work since is available only in a table in the supplementary.
- In Yus-Diez, the value of 4.05 is specific for 880 nm and is retrieved by comparing the Aethalometer with an offline polar photometer, which is not commercially available nor widely diffused.
- 3.22 is a second factor obtained using the offline polar photometer working as a MAAP. Since no detailed information is provided in the supplementary of Yus-Díez et al. (2021), I believe that 3.22 is calculated normalizing the absorption of the offline polar photometer to the absorption of the MAAP.
- The use of a wavelength-dependent C, is justified in this specific case since SSA values are quite high at PDM. In this SSA region, C values might drastically increase.
- If a wavelength-dependent C is used at 880 nm, I imagine that the ap used to calculate SSA at 635, 525 and 450 nm are corrected with a wavelength-dependent C. Same applies to AAE and SAE.
- First submission: The mean σap,880 was 0.27 Mm−1 (L220). Second submission: The mean σap,880 was 0.27 Mm−1 (L267). So, are the data corrected for a C value of 3.22 or not?
Unfortunately, none of these points are addressed in the manuscript nor in the supplementary. So, the authors are required to describe and justify more in detail their choices. This comment should be taken very seriously since the same problem was observed in the first round of reviews.

NOMENCLATURE
Work needs to be done to harmonise nomenclature:
- Although this might be interpreted as a single little mistake, it is an irritating one. The authors use “refractive BC” instead of “refractory BC” in the full text.
- Harmonise the nomenclature for scattering and absorption…. sca - abs or sp - ap

BANDRATIO
In my previous review, I mentioned that colour ratio might be used (potentially) to distinguish direct biomass-burning events. Although the analysis of colour ratio usually provides very noisy results, which are hard to interpret, it could be used to identify the potential influence of BB (Schwarz et al., 2006; Dahlkötter, 2014). So, the author’s statement “the color ratio only provides information on the presence of dustparticles” is fundamentally wrong. In the revised manuscript I did not expect to see a full colour-ratio analysis over two years, but, at least, a better justification on why it was not applied.

PYTHON CODE
The SP2 community urgently needs open-source software to treat the data. So, the authors should consider a more careful evaluation of the two codes. In this regard, I have some more comments:
- As written Text S1 suggest that the PSI toolkit is wrong while the python code is right. Indeed, the IGOR code has its limits, but it has been around for more than a decade, so I would be careful with some statements.
- The mass difference can be mostly attributed to the calibration curve. I would be very curious to see a comparison between number concentration.
- If the igor code counts invalid signal as real particles, shouldn’t the toolkit concentration be higher? Figure S1 shows the opposite.
- According to the values provided in the supplementary, analysing the same dataset with the IGOR toolkit would lead to a 20% lower MrBC and to a 20% higher MAC. I would not consider this difference to be negligible. If we consider that C values decreased from 3.63 to 3.22 (absorption increase of roughly 10%), the software and constant choices will introduce a MAC uncertainty of 30%.
- When addressing the differences between the two codes, the authors should be able to properly identify the causes. Without a proper evaluation/comparison of the two codes, the concluding statements could also be rewritten as: “The Python code might be less sensitive than the PSI toolkit due to a different selection of valid individual signals. …”
- “These different possibilities have not been explored in detail”. To be truly honest, this must have been done before the submission of the current manuscript. From my point of view, this is a crucial mistake from the authors.

ABSORPTION ENHANCEMENT AND MAC
As already raised in the first review, I have my doubts about the relevance of Eabs, as calculated and treated here. It is worth mentioning absorption enhancement if the available data allow quantifying the mixing state of BC…since the lensing effect is a direct consequence of coating formation. Without data on coating thickness, no real optical closure could be presented. I thus suggest the authors to: 1) focus on MAC variability in the full paper rather than EABS; 2) dedicate a very short paragraph, listing all possible uncertainty (RI in primis), to the overall Eabs that might characterize on average PDM.

SUMMARY AND IMPLICATIONS FOR CLIMATE MODELS
As already mentioned in the first round of reviews, the conclusions are too speculative. From my point of view, the new section worsened compared to the first submission. I strongly advise the authors to:
- Strictly and precisely describe their conclusive results. As it is, it is extremely hard to separate the results of this paper from previous works.
- Avoid any long discussions on global modelling and related parametrization of ageing, scavenging and absorption.

UNITS
Many figures feature an unusual notation for units. As an example, “ng.m-3”. From my experience, the use of a dot as a unit separator is unusual. None of the recently published ACP manuscripts presents this type of notation.

SPECIFIC COMMENTS
L253: please use the sectors indicated above.
L267: Since C was decreased from 3.63 to 3.22. I expect a value of ap higher than previous submission (also 0.27 Mm-1). Please verify your numbers.
L54: explain what Eabs is
L54-56: please, try to avoid such a long listing of references. My former supervisor would call this “lazy bibliography work”. Try to identify the works most pertinent works needed to send your message and help the reader identify who did what.
L71-76: This description might fit better in Section 2.1
L77: remove “in the indicated sections”
L92-93: Is this campaign called “Hygroscopic properties of black carbon”? Is this important information? If yes, please mention it in the abstract or introduction.
L100: sampled air
L101: inside the room or in the inlet?
L114 give a reference for the density.
L123-125: Here I have the same question as in the first round of comments. Mode1 is extrapolated from the Sp2 measurements in the 90-100 nm range? If this is true, is it reasonable to fit a lognormal curve on 10 nm?
L142: …,880,950 nm. Be consistent with line 137.
L217: The histogram in Figure S6 shows the dominance of periods with RH above 90%. I am wondering how many days have been removed from the two years period.
L253: please use the sectors indicated above.
L267: Since C was decreased from 3.63 to 3.22. I expect a value of ap higher than the previous submission (also 0.27 Mm-1). Please verify your numbers.
L264-284: There is incongruency between the sequence of properties discussed in the text and presented in figure 3. If I am not wrong, panels b and c are not discussed here. So, to be consistent, ap should be Figure 3b and sp should be Figure 3c.
L279-280: Remove the sentence about BC. When speaking of BC you can recall absorption. Try to keep a linear sequence of topics and figures.
L285-309 and F4: I have the impression that the graph does not provide a clear “speciation” of the aerosol optical properties. If the authors want to draw some evident conclusions from this analysis, the time resolution of the AAE, SAE and SSA should be decreased to at least 1 day. Alternatively, the Cappa method could be applied to summer-winter (on daily resolution)9, wet-dry and BL-FT cases (on hourly resolution)
F3: I would not fill the gaps between march and august 2020 for panel a, b and e. SAE is shortly discussed and AAE is not mentioned in the text. I guess they can both be removed from figure 3, since they are included in Figure 4 and discussed after. It is particularly not nice to see the wavelengths in legend not in decreasing or incresing order 635-450-525, please correct.
S3.3: Maybe this is a problem of my PDF reader, but the numbering of subsections is missing, as in the first submission
F6: since the concentration is normalized, only one colour scale is needed
L399-400: the diurnal variability of Eabs is poorly described. As it is, it does not provide crucial information and can be easily removed. Nonetheless, it might reflect, in terms of MrBC or BC/CO the daily cycle of BL and FT, as also shown by the authors in the reply to my first review. Excluding spring and summer, the diurnal analysis could be modified and used to introduce section 3.4.2. Clearly, this change will require some rethinking and additional work.
L413-414: I am glad that the authors implemented my comments. However, I think that the statement here is not exact. The goal of removing BL periods is to decrease the influence of air masses with different BC/CO ratios caused by different sources.
L415: Looking at Figure 8a, a value of 2.1 ng m−3 ppbv−1 is associated with precipitation-free back trajectories. In the second round of reviews, this sort of mistake should be avoided.
L418: please remind the readers that measurements that occurred at RH above 90% are removed.
L425-429:It would be nice to provide some numbers here. Otherwise is hard to compare with the studies cited (provide some numbers here too, please)
L434-441: The authors are considering only nucleation scavenging. Rightfully, fresh BC particles are hydrophobic, thus non-cloud-active. However, fresh and aged BC particles could be removed by wet scavenging below the cloud by impaction scavenging or inside the cloud by interstitial scavenging too. So, I would not indulge in a long discussion about supersaturation, when there might have been various competing removal mechanisms.
F8: Eabs is not discussed in the text. And I agree with this choice. But, why it is still shown in the figure? I would remove panel c and d and potentially replace it with Drbc, see following comment. F9: there is no need for two panels, show the absolute or normalized concentration. It is unclear to me how the RH lines are defined…RH>85% during precipitation period and RH<85% in no precipitation period? Potentially, Figure 9 could be merged with figure 8 removing the Eabs panels. Why it is “ng.m-3”? Remove this omnipresent point from units.
L444: check the subscript for ΔMrBC/ΔCO
L444-445: I already expressed my doubt on ΔMrBC calculated as MrBC. Figure 10a clearly shows that there is substantial variability in MrBC values depending on BL conditions. Especially in BL conditions. So, I still think that ΔMrBC should be calculated as the difference between the background concentration and the current concentration. In any case, as already mentioned, if you decide to keep the current calculation, the ratio must be called MrBC/ ΔCO. Otherwise, this is misleading. Moreover, I cannot find the number associated with the results shown in Figure 10c.
L446-448: No values given for Eabs. Eabs should be shown in panel c and not b. Please try to maintain the same sequence in the text and in the figures/panels.
L449-450: Please reformulate the sentence reporting the mean or median concentration….as written, it is weird
L452-454: unclear, please rephrase.
L459-460: Again, no values are provided.
L468-478: rBC loading and BC/OC are shown in Fig 10d and f not d and e
L479-491: I still have doubts about this subsection. First, I do not find a clear reason explaining the variability of eabs. Second, Section 3.4.2 is supposed to discuss FT/BL dynamics, which is not treated in this part of the text and in Figure 11. In my opinion, all these parts should be removed.

REFERENCES
Dahlkötter, F.: Airborne observations of black carbon aerosol layers at mid-latitudes, Technische Universität München, 2014.
Schwarz, J. P., Gao, R. S., Fahey, D. W., Thomson, D. S., Watts, L. A., Wilson, J. C., Reeves, J. M., Darbeheshti, M., Baumgardner, D. G., Kok, G. L., Chung, S. H., Schulz, M., Hendricks, J., Lauer, A., Kärcher, B., Slowik, J. G., Rosenlof, K. H., Thompson, T. L., Langford, A. O., Loewenstein, M., and Aikin, K. C.: Single-particle measurements of midlatitude black carbon and light-scattering aerosols from the boundary layer to the lower stratosphere, J. Geophys. Res. Atmospheres, 111, D16207, https://doi.org/10.1029/2006JD007076, 2006.
Yus-Díez, J., Bernardoni, V., Močnik, G., Alastuey, A., Ciniglia, D., Ivančič, M., Querol, X., Perez, N., Reche, C., Rigler, M., Vecchi, R., Valentini, S., and Pandolfi, M.: Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: a multi-instrumental approach, Atmospheric Meas. Tech., 14, 6335–6355, https://doi.org/10.5194/amt-14-6335-2021, 2021.

Hide

ED: Reconsider after major revisions (14 Aug 2023) by Andreas Petzold

Dear Sarah, dear Cyrielle

after having sent the revised manuscript to reviewers, I received the below attached review of your revised manuscript.
Please respond carefully to the comments of the reviewer, who has worked very hard to review your manuscript.
Responding to the points raised by the reviewer is mandatory for publication.

Best wishes,

Andreas

REVIEW Preprint egusphere-2023-570

I am glad that Tinorua and co-authors incorporated some of my previous suggestions. In some parts, the manuscript’s quality and readability improved since the first submission. However, this version still suffers from very similar flaws compared to the first draft. The presentation of the results is chaotic since there is little cohesion between the text and the figures. I notice an overall superficiality in justifying technical choices, presenting the data and interpreting the results. Finally, the results are not clearly summarized in the conclusion section, which is a very confusing mix of results, references and speculations. Considering the number of specific comments that can be found as follows (editing, grammar, nomenclature, sequence of figures, etc…), I have the impression that the manuscript was not carefully controlled before resubmission. Despite the high interest in the dataset, I cannot recommend the publication of the manuscript in ACP. I leave the choice of full rejection or resubmission after major changes to the editor, waiting for the pending reviews from other referees.

MAJOR COMMENTS

MULTIPLE SCATTERING CORRECTION
The C value was changed from 3.63 to 3.22 according to Yus-Díez et al. (2021). Considering the importance of this change and the direct effect on absorption coefficient and MAC, the choice should be explained better, and should not be based, solely, on the fact that Montsec d’Ares is a mountaintop site 200 km away from PDM. More specific comments:
- In the main text of Yus-Díez et al. (2021), I could find values between 2.51 and 2.36 for Montsec d’Ares. These values are calculated using a different type of filter and normalized against the MAAP at one single wavelength.
- Finding the value 3.22 in Yus-Diez requires some work since is available only in a table in the supplementary.
- In Yus-Diez, the value of 4.05 is specific for 880 nm and is retrieved by comparing the Aethalometer with an offline polar photometer, which is not commercially available nor widely diffused.
- 3.22 is a second factor obtained using the offline polar photometer working as a MAAP. Since no detailed information is provided in the supplementary of Yus-Díez et al. (2021), I believe that 3.22 is calculated normalizing the absorption of the offline polar photometer to the absorption of the MAAP.
- The use of a wavelength-dependent C, is justified in this specific case since SSA values are quite high at PDM. In this SSA region, C values might drastically increase.
- If a wavelength-dependent C is used at 880 nm, I imagine that the ap used to calculate SSA at 635, 525 and 450 nm are corrected with a wavelength-dependent C. Same applies to AAE and SAE.
- First submission: The mean σap,880 was 0.27 Mm−1 (L220). Second submission: The mean σap,880 was 0.27 Mm−1 (L267). So, are the data corrected for a C value of 3.22 or not?
Unfortunately, none of these points are addressed in the manuscript nor in the supplementary. So, the authors are required to describe and justify more in detail their choices. This comment should be taken very seriously since the same problem was observed in the first round of reviews.

NOMENCLATURE
Work needs to be done to harmonise nomenclature:
- Although this might be interpreted as a single little mistake, it is an irritating one. The authors use “refractive BC” instead of “refractory BC” in the full text.
- Harmonise the nomenclature for scattering and absorption…. sca - abs or sp - ap

BANDRATIO
In my previous review, I mentioned that colour ratio might be used (potentially) to distinguish direct biomass-burning events. Although the analysis of colour ratio usually provides very noisy results, which are hard to interpret, it could be used to identify the potential influence of BB (Schwarz et al., 2006; Dahlkötter, 2014). So, the author’s statement “the color ratio only provides information on the presence of dustparticles” is fundamentally wrong. In the revised manuscript I did not expect to see a full colour-ratio analysis over two years, but, at least, a better justification on why it was not applied.

PYTHON CODE
The SP2 community urgently needs open-source software to treat the data. So, the authors should consider a more careful evaluation of the two codes. In this regard, I have some more comments:
- As written Text S1 suggest that the PSI toolkit is wrong while the python code is right. Indeed, the IGOR code has its limits, but it has been around for more than a decade, so I would be careful with some statements.
- The mass difference can be mostly attributed to the calibration curve. I would be very curious to see a comparison between number concentration.
- If the igor code counts invalid signal as real particles, shouldn’t the toolkit concentration be higher? Figure S1 shows the opposite.
- According to the values provided in the supplementary, analysing the same dataset with the IGOR toolkit would lead to a 20% lower MrBC and to a 20% higher MAC. I would not consider this difference to be negligible. If we consider that C values decreased from 3.63 to 3.22 (absorption increase of roughly 10%), the software and constant choices will introduce a MAC uncertainty of 30%.
- When addressing the differences between the two codes, the authors should be able to properly identify the causes. Without a proper evaluation/comparison of the two codes, the concluding statements could also be rewritten as: “The Python code might be less sensitive than the PSI toolkit due to a different selection of valid individual signals. …”
- “These different possibilities have not been explored in detail”. To be truly honest, this must have been done before the submission of the current manuscript. From my point of view, this is a crucial mistake from the authors.

ABSORPTION ENHANCEMENT AND MAC
As already raised in the first review, I have my doubts about the relevance of Eabs, as calculated and treated here. It is worth mentioning absorption enhancement if the available data allow quantifying the mixing state of BC…since the lensing effect is a direct consequence of coating formation. Without data on coating thickness, no real optical closure could be presented. I thus suggest the authors to: 1) focus on MAC variability in the full paper rather than EABS; 2) dedicate a very short paragraph, listing all possible uncertainty (RI in primis), to the overall Eabs that might characterize on average PDM.

SUMMARY AND IMPLICATIONS FOR CLIMATE MODELS
As already mentioned in the first round of reviews, the conclusions are too speculative. From my point of view, the new section worsened compared to the first submission. I strongly advise the authors to:
- Strictly and precisely describe their conclusive results. As it is, it is extremely hard to separate the results of this paper from previous works.
- Avoid any long discussions on global modelling and related parametrization of ageing, scavenging and absorption.

UNITS
Many figures feature an unusual notation for units. As an example, “ng.m-3”. From my experience, the use of a dot as a unit separator is unusual. None of the recently published ACP manuscripts presents this type of notation.

SPECIFIC COMMENTS
L253: please use the sectors indicated above.
L267: Since C was decreased from 3.63 to 3.22. I expect a value of ap higher than previous submission (also 0.27 Mm-1). Please verify your numbers.
L54: explain what Eabs is
L54-56: please, try to avoid such a long listing of references. My former supervisor would call this “lazy bibliography work”. Try to identify the works most pertinent works needed to send your message and help the reader identify who did what.
L71-76: This description might fit better in Section 2.1
L77: remove “in the indicated sections”
L92-93: Is this campaign called “Hygroscopic properties of black carbon”? Is this important information? If yes, please mention it in the abstract or introduction.
L100: sampled air
L101: inside the room or in the inlet?
L114 give a reference for the density.
L123-125: Here I have the same question as in the first round of comments. Mode1 is extrapolated from the Sp2 measurements in the 90-100 nm range? If this is true, is it reasonable to fit a lognormal curve on 10 nm?
L142: …,880,950 nm. Be consistent with line 137.
L217: The histogram in Figure S6 shows the dominance of periods with RH above 90%. I am wondering how many days have been removed from the two years period.
L253: please use the sectors indicated above.
L267: Since C was decreased from 3.63 to 3.22. I expect a value of ap higher than the previous submission (also 0.27 Mm-1). Please verify your numbers.
L264-284: There is incongruency between the sequence of properties discussed in the text and presented in figure 3. If I am not wrong, panels b and c are not discussed here. So, to be consistent, ap should be Figure 3b and sp should be Figure 3c.
L279-280: Remove the sentence about BC. When speaking of BC you can recall absorption. Try to keep a linear sequence of topics and figures.
L285-309 and F4: I have the impression that the graph does not provide a clear “speciation” of the aerosol optical properties. If the authors want to draw some evident conclusions from this analysis, the time resolution of the AAE, SAE and SSA should be decreased to at least 1 day. Alternatively, the Cappa method could be applied to summer-winter (on daily resolution)9, wet-dry and BL-FT cases (on hourly resolution)
F3: I would not fill the gaps between march and august 2020 for panel a, b and e. SAE is shortly discussed and AAE is not mentioned in the text. I guess they can both be removed from figure 3, since they are included in Figure 4 and discussed after. It is particularly not nice to see the wavelengths in legend not in decreasing or incresing order 635-450-525, please correct.
S3.3: Maybe this is a problem of my PDF reader, but the numbering of subsections is missing, as in the first submission
F6: since the concentration is normalized, only one colour scale is needed
L399-400: the diurnal variability of Eabs is poorly described. As it is, it does not provide crucial information and can be easily removed. Nonetheless, it might reflect, in terms of MrBC or BC/CO the daily cycle of BL and FT, as also shown by the authors in the reply to my first review. Excluding spring and summer, the diurnal analysis could be modified and used to introduce section 3.4.2. Clearly, this change will require some rethinking and additional work.
L413-414: I am glad that the authors implemented my comments. However, I think that the statement here is not exact. The goal of removing BL periods is to decrease the influence of air masses with different BC/CO ratios caused by different sources.
L415: Looking at Figure 8a, a value of 2.1 ng m−3 ppbv−1 is associated with precipitation-free back trajectories. In the second round of reviews, this sort of mistake should be avoided.
L418: please remind the readers that measurements that occurred at RH above 90% are removed.
L425-429:It would be nice to provide some numbers here. Otherwise is hard to compare with the studies cited (provide some numbers here too, please)
L434-441: The authors are considering only nucleation scavenging. Rightfully, fresh BC particles are hydrophobic, thus non-cloud-active. However, fresh and aged BC particles could be removed by wet scavenging below the cloud by impaction scavenging or inside the cloud by interstitial scavenging too. So, I would not indulge in a long discussion about supersaturation, when there might have been various competing removal mechanisms.
F8: Eabs is not discussed in the text. And I agree with this choice. But, why it is still shown in the figure? I would remove panel c and d and potentially replace it with Drbc, see following comment. F9: there is no need for two panels, show the absolute or normalized concentration. It is unclear to me how the RH lines are defined…RH>85% during precipitation period and RH<85% in no precipitation period? Potentially, Figure 9 could be merged with figure 8 removing the Eabs panels. Why it is “ng.m-3”? Remove this omnipresent point from units.
L444: check the subscript for ΔMrBC/ΔCO
L444-445: I already expressed my doubt on ΔMrBC calculated as MrBC. Figure 10a clearly shows that there is substantial variability in MrBC values depending on BL conditions. Especially in BL conditions. So, I still think that ΔMrBC should be calculated as the difference between the background concentration and the current concentration. In any case, as already mentioned, if you decide to keep the current calculation, the ratio must be called MrBC/ ΔCO. Otherwise, this is misleading. Moreover, I cannot find the number associated with the results shown in Figure 10c.
L446-448: No values given for Eabs. Eabs should be shown in panel c and not b. Please try to maintain the same sequence in the text and in the figures/panels.
L449-450: Please reformulate the sentence reporting the mean or median concentration….as written, it is weird
L452-454: unclear, please rephrase.
L459-460: Again, no values are provided.
L468-478: rBC loading and BC/OC are shown in Fig 10d and f not d and e
L479-491: I still have doubts about this subsection. First, I do not find a clear reason explaining the variability of eabs. Second, Section 3.4.2 is supposed to discuss FT/BL dynamics, which is not treated in this part of the text and in Figure 11. In my opinion, all these parts should be removed.

REFERENCES
Dahlkötter, F.: Airborne observations of black carbon aerosol layers at mid-latitudes, Technische Universität München, 2014.
Schwarz, J. P., Gao, R. S., Fahey, D. W., Thomson, D. S., Watts, L. A., Wilson, J. C., Reeves, J. M., Darbeheshti, M., Baumgardner, D. G., Kok, G. L., Chung, S. H., Schulz, M., Hendricks, J., Lauer, A., Kärcher, B., Slowik, J. G., Rosenlof, K. H., Thompson, T. L., Langford, A. O., Loewenstein, M., and Aikin, K. C.: Single-particle measurements of midlatitude black carbon and light-scattering aerosols from the boundary layer to the lower stratosphere, J. Geophys. Res. Atmospheres, 111, D16207, https://doi.org/10.1029/2006JD007076, 2006.
Yus-Díez, J., Bernardoni, V., Močnik, G., Alastuey, A., Ciniglia, D., Ivančič, M., Querol, X., Perez, N., Reche, C., Rigler, M., Vecchi, R., Valentini, S., and Pandolfi, M.: Determination of the multiple-scattering correction factor and its cross-sensitivity to scattering and wavelength dependence for different AE33 Aethalometer filter tapes: a multi-instrumental approach, Atmospheric Meas. Tech., 14, 6335–6355, https://doi.org/10.5194/amt-14-6335-2021, 2021.

Hide

AR by Sarah Tinorua on behalf of the Authors (10 Oct 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (05 Nov 2023) by Andreas Petzold

RR by Anonymous Referee #1 (16 Nov 2023)

ED: Publish subject to minor revisions (review by editor) (01 Dec 2023) by Andreas Petzold

AR by Sarah Tinorua on behalf of the Authors (08 Dec 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (10 Dec 2023) by Andreas Petzold

AR by Sarah Tinorua on behalf of the Authors (11 Dec 2023)

Journal article(s) based on this preprint

08 Feb 2024

Higher absorption enhancement of black carbon in summer shown by 2-year measurements at the high-altitude mountain site of Pic du Midi Observatory in the French Pyrenees

Sarah Tinorua, Cyrielle Denjean, Pierre Nabat, Thierry Bourrianne, Véronique Pont, François Gheusi, and Emmanuel Leclerc

Atmos. Chem. Phys., 24, 1801–1824, https://doi.org/10.5194/acp-24-1801-2024,https://doi.org/10.5194/acp-24-1801-2024, 2024

Short summary

Sarah Tinorua, Cyrielle Denjean, Pierre Nabat, Thierry Bourrianne, Véronique Pont, François Gheusi, and Emmanuel Leclerc

Supplement

https://doi.org/10.5194/egusphere-2023-570-supplement

Sarah Tinorua, Cyrielle Denjean, Pierre Nabat, Thierry Bourrianne, Véronique Pont, François Gheusi, and Emmanuel Leclerc

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Aug 2023	38	18	0	56
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Cumulative views and downloads (calculated since 11 Apr 2023)

Month	HTML	PDF	XML	Total
Apr 2023	299	89	8	396
May 2023	61	20	6	87
Jun 2023	24	13	0	37
Jul 2023	64	26	14	104
Aug 2023	38	18	0	56
Sep 2023	56	29	3	88
Oct 2023	49	19	5	73
Nov 2023	28	16	3	47
Dec 2023	30	21	4	55
Jan 2024	30	16	1	47
Feb 2024	4	13	0	17
Mar 2024	0
Apr 2024	0
May 2024	0
Jun 2024	0
Jul 2024	0
Aug 2024	0
Sep 2024	0

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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Short summary

Two years of Black Carbon (BC) and aerosols optical and microphysical measurements have been conducted at a french high-altitude site, where numerous complex interactions between BC, radiation, clouds and snow impact climate. We observed strong seasonal BC properties variations, with a higher absorption enhancement in summer compared to winter. The combination of BC emission sources, transport pathways, atmospheric dynamics and chemical processes explains the BC light absorption seasonality.


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