Overall, this is a very well written and structured manuscript that brings new insights on the sources and variability of BC and its' properties in central South-America. The manuscript fits in the scope of the journal and is recommend for publication subject to technical corrections.

General comments:

• Please indicate what "time zone" is used in the manuscript. This is critical especially for interpretation of daily variations. Are the measurements done in UTC or local time? If time is local, how much that deviates from UTC? Was the time shift considered for those data taken from other sources (e.g. EBAS or meteorological observations)?
• Section "2.3 sampling methods" is missing description on sample drying and RH conditions. It is also missing information on how the particulate mass (PM) concentrations were determined, were the filters weighted, which balance and RH were used? How the uncertainties were calculated? This is important since it impacts the eBC mass fraction calculation.
• The last part of the manuscript was slightly challenging to follow due to several missing figures and tables in supplement. Please revise this carefully.

Specific comments:

Please, check the correct spelling of all the co-authors.

L103: “it is also intended” seems like repetition, consider re-phrasing.

L119: What is meant here with temperature amplitude? Max-min?

L150: Was the “basic meteorological station” then solely an anemometer? Please clarify.

L152: Which “other meteorological variables” were included? These could be listed.

L167: replace m2->m3

L.265: “the assumption that the properties of the urban aerosol do not change drastically on their transport to CHC-GAW”  Which properties of the urban aerosol this refers to? Based on table S2, even during daytime BC aerosol optical properties (MAC) were very different at the sites. How much could this add uncertainty on the defined Cf? Do you have an idea of the SSA at these sites?

L.279-280: “The babs estimated using the Cf factors selected for each model of AE31 decrease the instrumental difference to roughly 27%.” Please, clarify. What are different models of AE31 and what are the instruments for which the difference is 27%?

L336. replace WB->BB

L341-343: “The pair of wavelengths chosen to apply in this method to apportion the contribution of local vehicular emissions (also known as liquid fuel) from the regional agricultural biomass burning emissions (also known as solid fuel) were 470 and 950 nm.” Was there any particular reason for this choice?

L.417 “appear relatively elevated” : compared to what? In previous paragraph the authors write "do not stand out as alarming" which could be interpreted partly contradictory.

Table 2: Add information on the inlet cut-size (PM10?) after eBC, similar to what is given for EC. Were the 24h-samples of EC for CHC-GAW completely omitted from the analysis? They appear in the methods so please clarify.

L457. replace: suset->sunset

L520. “This change in the AAE during this period of the day takes place when eBC mass concentrations reach their minimum, thus, no significant impact in absorption was observed at 880 nm.” Message from this sentence is not clear. It raises a question if we are expecting dust to be visible at 880nm?

L541. “it overestimated the mixing state of the urban aerosol” here one must remember also the uncertainties in Cf.

L567. “Nevertheless, the spectral dependence of MACEC and MACrBC values is different.” Could this be clarified and opened a bit more?

L591. Fig S6 is missing.

L618 Fig S7 is missing.

L662-663: Fig S8 and Table S3 are missing

L672 S9 missing.

L701 Table S4 missing.

Supplement Table S2: replace ii->i

The authors have adopted different methods to analyze the concentration and sources of black carbon in the metropolitan area of La Paz and El Alto, Bolivia, and has compared the performance of different measurement methods. Overall, this article is of certain value and is very suitable for publication in ACP. I only have some minor revision suggestions:

1. Some studies have shown that the Single Particle Soot Photometer, when relying on scattering measurements to determine optical particle size and mixing state, can be influenced by microphysical characteristics. Please refer to relevant explanations for further clarification.

References

Wu, Y., Cheng, T., Zheng, L., Zhang, Y., and Zhang, L.: Particle size amplification of black carbon by scattering measurement due to morphology diversity, Environmental Research Letters, 18, 024 011, https://doi.org/10.1088/1748-9326/acaede, 2023.

Luo, J., Hu, M., Qiu, J., Li, K., He, H., Sun, Y., and Geng, X.: Technical note: Numerical quantification of the mixing states of partially-coated black carbon based on the single-particle soot photometer: Implication for global radiative forcing, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-1155, 2024.

2. Some studies have also found that the Aethalometer model, when used for tracing the sources of black carbon, can be influenced by the microphysical properties of black carbon. Please cite relevant literature to support this statement.

References

Virkkula, A. (2021). Modeled source apportionment of black carbon particles coated with a light-scattering shell. Atmospheric Measurement Techniques, 14(5), 3707–3719.

Luo, J., Li, Z., Qiu, J., Zhang, Y., Fan, C., Li, L., Wu, H., Zhou, P., Li, K., and Zhang, Q.: The Simulated Source Apportionment of Light Absorbing Aerosols: Effects of Microphysical Properties of Partially-Coated Black Carbon, J. Geophys. Res.-Atmos., 128, e2022JD037291, https://doi.org/10.1029/2022JD037291, 2023.

Luo, J., Li, D., Wang, Y., Sun, D., Hou, W., Ren, J., Wu, H., Zhou, P., and Qiu, J.: Quantifying the effects of the microphysical properties of black carbon on the determination of brown carbon using measurements at multiple wavelengths, Atmos. Chem. Phys., 24, 427–448, https://doi.org/10.5194/acp-24-427-2024, 2024.

3. Many researchers have utilized various instruments to measure and study black carbon in different regions. To further elaborate on the novelty of this paper, please discuss the unique characteristics of black carbon in the metropolitan area of La Paz and El Alto, Bolivia, compared to previous studies in other regions and similar settings.

4. What are the specific implications of black carbon measurements in this region for understanding regional and global climate, as well as air quality changes? Additionally, what recommendations would you make for future black carbon measurements?