Review for the manuscript: New Particle Formation dynamics in the central Andes: Contrasting urban and mountain-top environments by Diego Aliaga et al.

In this study measurements obtained during March 19 – May 31, 2018 (65 days), that correspond to the transition period from the wet to the dry season, are investigated for two sites in the Southern hemisphere (Bolivian Central Andes) including a mountain-top station (CHC) and an urban background site (EAC). The main objective of this work was to expand the current understanding of new particle formation (NPF) in the central Andes by simultaneously comparison of NPF events at the two interconnected sites (with different altitudes) and by additionally application of a recently developed “nanoparticle ranking analysis” (Aliaga et al., 2023) to evaluate the probability and intensity of NPF occurrence simultaneously at both sites, resulting in a joint distribution.

The manuscript is interesting, well written/ illustrated, describes careful experimental work and is worthy of being published in AR.

I have mostly the following minor revisions to suggest:

Minor comments:

In the abstract the four group categories are mentioned regarding the daily maximum concentration of 4-7 nm particles as high at both sites, lower at one etc. In the main text (lines 462-467) other parameters are also considered for naming the groups and this also should be stated.  I would suggest adding those names (intense, cloudy etc.) in the abstract (lines 44-45) as well in parenthesis, as it is not very clear to the reader which is which.

For example: (A) high at both sites (intense NPF case), (B) medium at both (polluted), (C) high at EAC but low at CHC (volcanic), (D) and low at both (cloudy).

Also, in the abstract the D) cloudy related group is not mentioned at all. Maybe a line would be nice to be included.

Additionally, I would suggest for lines 461-468 to present the 4 cases as the classification, meaning, 1. intense, 2. polluted, 3. volcanic and 4. cloudy.

Lines 72, 321, 733 etc. A punctuation mark is missing.

Line 334. The parenthesis in reference is not necessary.

Line 547. The long –– symbol should be changed to –.

Line 560. J4 should be J₄

Line 721. “EAC ( concentrations” should be “EAC (concentrations”

Line 725. The J4 values should be 2.2 and 9.2 cm-3 s-1for CHC and EAC, respectively.

Lines 881-882. Please rephrase. Not very clear to the reader.

Line 917. Add “days” after “Polluted”

In the introduction authors state:

“For example, we need to better understand the chemical composition of the precursor gases involved in nucleation and growth, as well as the composition of the aerosols formed during these events.” But this is not addressed in the current work.

References.

Aliaga, D., Tuovinen, S., Zhang, T., Lampilahti, J., Li, X., Ahonen, L., Kokkonen, T., Nieminen, T., Hakala, S., Paasonen, P., Bianchi, F., Worsnop, D., Kerminen, V.-M., and Kulmala, M.: Nanoparticle ranking analysis: determining new particle formation (NPF) event occurrence and intensity based on the concentration spectrum of formed particles, Aerosol Res., 1, 81–92, https://doi.org/10.5194/ar-1-81-2023, 2023.

Review for the manuscript: New Particle Formation dynamics in the central Andes: Contrasting urban and mountain-top environments by Diego Aliaga et al.

This study investigates the Atmospheric New Particle Formation (NPF) in the Central Andes, focusing on differences between mountain-top and urban sites. ​ This study examines measurements taken at two sites in the Southern Hemisphere (Bolivian Central Andes): a mountain-top station (CHC) and an urban background site (EAC). The measurements were taken from March 19 to May 31, 2018, which corresponds to the dry season's transition. Classification of study days into four categories based on NPF intensity for detailed analysis. Identification of key indicators and detailed analysis of categories to understand NPF processes in the region, especially the applicability of “nanoparticle ranking analysis” proposed by Kulmala et al. (2022). ​ It provides valuable insights into the factors influencing particle formation, particularly in exploring the impacts of urban and mountain environments on NPF processes. The classification of study days into distinct categories based on NPF intensity allows for a comprehensive analysis of atmospheric conditions and their impact on NPF, shedding light on the complex interplay between various factors. Nevertheless, before it is published, the manuscript needs considerable refinement.

Comments:

1. The present abstract ought to delve into the dynamics of the mountain-valley wind in a diurnal cycle, given its crucial role in the NPF process at elevated altitudes.
2. Some insight into the significance of the findings from the mountain observations should be provided in the introduction section. in particular over India's Western Ghats (Victor et al., 2024, Sebastian et al., 2022)
3. Victor N J, Pallavi Buchunde, Mathew Sebastian,Vijay P. Kanawade, Devendraa Siingh, Subrata Mukherjee, Swapnil S. Potdar, T. Dharmaraj, and Govindan Pandithurai (2024), Characteristics of new particle formation events in a mountain semi-rural location in India, Atmospheric Environment, Volume 324, 1 May 2024, 120414, https://doi.org/10.1016/j.atmosenv.2024.120414
4. Sebastian, M., Kanawade, V.P., Soni, V.K., Asmi, E., Westervelt, D.M., Vakkari, V., Hyv¨arinen, A.P., Pierce, J.R., Hooda, R.K., 2021a. New particle formation and growth to climate-relevant aerosols at a background remote site in the western himalaya. J. Geophys. Res. Atmos. 126 https://doi.org/10.1029/2020JD033267.
5. Line 70: Kerminen et al., 2018 and Lee et al., 2019 may be cited
6. Lee, S.-H., Gordon, H., Yu, H., Lehtipalo, K., Haley, R., Li, Y., & Zhang, R. (2019). New particle formation in the atmosphere: From molecular clusters to global climate. Journal of Geophysical Research: Atmospheres, 124, 7098–7146. https://doi.org/10.1029/2018JD029356
7. 110: There have been reports that indicate mixed air leads to more NPF, while clear air also occasionally delivers greater NPF. How does this fit into this paragraph?
8. Line 215-220: NAIS measurement methods can be made shorter by including appropriate citations, as this information is widely available.
9. If details have already been mentioned in Aliaga et al., (2021), then avoid repetition or compress if necessary for the reader. Simple statements, elaborating less significant details, and repetition of the same citation may be avoided by taking the journal's standard and the length of the MS into consideration. For example, lines 350, 335 may be avoided.
10. Line no. 390-395 may be removed, the mode-fitting method is quite known, and sufficient citation also provided. Moreover, as mentioned, it is not suitable for the present study.
11. Given the number of analyses, parameters, and presumptions used here, it is strongly advised to employ a flow chart with a few brief descriptions. This will help the reader to better grasp the technique and keep the text to a minimum.
12. Line number 475 to 490 also be represented as a chart or table, so that the reader can easily understand its significance.
13. It seems the cloud cover or fraction between CHC and EAC varied much, for example, SW at CHC shows the drift from the normal curve is more visible much later, of 12 LT and the temperature at EAC doesn’t seem to differ much from the average curve. Hence, in the in the morning hours, where nucleation is likely to happen, at both sites, the atmosphere was exposed to either a clear sky or enough sunlight or solar radiation for the photochemical activity. Moreover, CS and J4 at EAC for intense-NPF and cloud cover-NPF almost have same pattern, so the question comes what the impact of cloud cover at EAC is. So to clear this uncertainty, it would be great if hourly cloud fraction data to be presented.
14. In conclusion: In addition to the fact that all of the measures and numbers presented have already been covered in previous sections, they may be constrained to focus solely on the conclusions drawn from the metrics. This makes it possible for readers to focus solely on the study's primary findings.
15. In conclusion, a small paragraph may be devoted to summarizing the findings of the entire investigation in relation to the high-altitude readings.