general comments:

The current work reports on ReaxFF simulations of acetylene from 1350-1800 K for large systems (1000 molecules) for long time spans (10 ns). The work reports statistics of molecules formed over time with emphasis on the formation of incipient soot, i.e. molecule growing to large species with a molecular weight over roughly 200 up to about 1000 in this work. The analysis of the ReaxFF simulations is quite detailed and some kinds of molecules are found that have not yet been reported in similar studies at different conditions (e.g. species with small rings and long aliphatic chains). There is some comparison to and new insight compared to previous ReaxFF simulations of soot formation. However, there is little comparison to experiments results (some are mentioned and some disagreement is found, but not discussed in much detail (p. 19)) and none to soot modelling based on kinetic mechanisms / models, though many exist for acetylene pyrolysis ("acetylene soot formation models" in google scholar yields many results with promising titles for work on and with such models). I think such a comparison would strengthen the work considerably, together with a quantum mechanical validation of new pathways or at least a note of caution that the results pertain to the ReaxFF model used, and not necessarily to reality.  

specific comments:

P 5: Please make the scripts used for analysis of the MD data available or add more information on the algorithms used.

P 8: “Incipient soot is defined by the formation …” providing this definition earlier (before talking about incipient soot) may make it easier to follow the introduction.

P 10: “The faster consumption rate of the C6-C10 molecules could be attributed to their larger projected area compared to C1-C5 compounds, rendering them more likely to be scavenged by the

large incipient soot.” (And a similar statement in the following paragraph) This seems very speculative to me. Considering the much higher number of C1-5 molecules and the moderate size difference, I would expect the opposite (more collisions). Please check by e. g. calculating collision frequencies with a simple kinetic gas theory model if this is the correct reason.

P 17: “cyclopropyne (Saxe and Schaefer 1980)” Is this molecule real or a ReaxFF artefact?  According to Saxe and Schefer, the singlet state is unstable and the triplet state is metastable at a quite high energy. https://en.wikipedia.org/wiki/Cycloalkyne says: “There is little experimental evidence supporting the existence of cyclobutyne (C4H4) or cyclopropyne (C3H2), aside from studies reporting the isolation of an osmium complex with cyclobutyne ligands.[4]”. A few lines later “… indicating they are relatively stable in nature.” Is that a valid conclusion? I would say the results indicate that they (cyclopropyne molecules) are stable at the ReaxFF level, but not necessarily in nature.

P 22: “… allowing for a broader and more accurate exploration of the pathways” I agree to “broader”, but I am sceptical regarding “more accurate” without QM or exp validation, see my previous comments

P 23: “Tracking the pathway of formation of these species could reveal new detailed chemical routes that occur during soot nucleation, which might have not been extensively considered in existing kinetic models, thereby expanding the current understanding of soot formation pathways.” I think this would be really useful. Can this be added to the current work or at least the simulation (raw) data provided that are needed for such an analysis?

technical corrections:

P 3: “that shoot growth” => soot.

Questions for review:

• Does the manuscript represent a substantial contribution to scientific progress within the scope of Aerosol Research (substantial new concepts, ideas, methods, or data)?

The manuscript mainly presents new data for simulations under conditions different from those of previous works. Similar simulation and analysis concepts and methods have been applied before.  

• Are the scientific approach and applied methods valid? Are the results discussed in an appropriate and balanced way (consideration of related work, including appropriate references)?

As mentioned before, more validation should be performed to ensure that the results are relevant for real systems, not just for the REaxFF model system. Therefore, I suggest a mayor revision.

• Are the scientific results and conclusions presented in a clear, concise, and well structured way (number and quality of figures/tables, appropriate use of English language)?

Yes, this is mainly the case.

The authors presented a reactive MD study of soot inception and early surface growth during acetylene pyrolysis at four temperatures between 1350 and 1800 K relevant to typical hydrocarbon flames. The objective of this study is to provide a more general view of soot inception by investigating the evolution of a reaction system containing C2H2 molecules, rather than assuming some intermediate species or PAHs as the initial condition.

Overall, the analysis and discussion of the results are comprehensive and offer useful insights into chemical evolution of the simulation system associated with soot inception and early surface growth. However, it is somewhat disappointed to notice that the authors did not provide the details of soot inception, such as the precursor species involved, even though their results should be able to provide such details by examining the numerical results slightly prior to the occurrence of the soot particle shown in Fig. 1.

The authors paid close attention to the evolution of 3-, 5-, and 6-member rings in their results, but did not mention if there are other polycyclic aromatic species in the system, such as 4- or 7-member rings.

The authors also noticed that their results are somewhat different from those reported in the literature for different fuels and at different temperatures (Wang et al., 2022a, Wang et al., 2022b, Zhao et al., 2020). Can the authors speculate if the chemical  details of soot formation and early growth will be different for different hydrocarbons?

Minor points:

• In line 17 on page 3, ‘shoot’ should be soot.
• In the line below Fig. 5, why do you call the results in Fig. 6 ‘the cumulative number …’ rather than ‘the number …’?
• In the first paragraph on page 16, Figure S15a and Figure 15b seem messed up.