Review of “Enhancing particle number concentration modelling accuracy in China by incorporating various nucleation parameterization schemes into the CMAQ version 5.3.2 model” by Mao et al.

The default BHN nucleation scheme in CMAQ model (version 5.3.2) underestimates particle number concentrations. To address this, Mao et al. integrated and tested multiple parameterizations (BHN, THN, IMN, DMA, SumBTD, and SumID) into CMAQ v5.3.2. Among these, the SumID scheme (IMN+DMA) proved most effective, substantially improving the simulation of number concentrations and NPF events in Beijing and Nanjing. The enhanced model reduces the underestimation by 36–84% compared to observations, in contrast to the default BHN scheme, which misses 70–78%. Results highlight the dominant role of IMN (~56% in Beijing, ~28% in Nanjing) and the significant contribution of DMA (~28–29%). The IMN shows a strong diurnal variability, with higher concentrations during the daytime and lower at night, while DMA specifically influences the morning and evening peaks. Overall, the study demonstrates that incorporating multiple nucleation pathways improves the ability of the model (CMAQ) to represent NPF processes and quantify the contributions of individual nucleation mechanisms. Furthermore, the findings suggest that nucleation mechanisms vary between regions, emphasizing the importance of multiple nucleation parametrization schemes which this paper demonstrates through the performed case studies for the two different regions.

The study outlines a comprehensive overview of different nucleation parametrization schemes, underscoring the most effective which contribute substantially to the model advancements and future applications. Overall, the paper is clearly written and logically organized, however, some modest technical improvements could further enhance the readability. I have some comments/suggestions/questions, mostly for the clarification, that should be addressed before publication.

Comments:

General remark: several acronyms are used throughout the manuscript, but not all are defined upon first use. For the clarity and better readability, I recommend that the authors ensure all acronyms are spelled out when they first appear in the text.

In your results you have shown the comparison between different nucleation schemes for Aitken mode simulations highlighting the relatively high performance by IMN, SumBTD and SumID. However, the manuscript does not provide reasoning for why these schemes outperform the default BHN parametrization especially for the Aitken mode simulations. I suggest to discuss it briefly as it would help readers to better understand the difference in model performance.

Line 329: In the statement, “fine particles are rapidly removed due to condensation and coagulation”, the term “removed” is not accurate. In aerosol dynamics, “removal” typically refers to dry/wet deposition or scavenging. Microphysical processes such as condensation and coagulation instead contribute to particle transformation rather than removal.

If I understand correctly (otherwise please clarify), there are some existing studies where CTMs with detailed aerosol microphysics have been applied (for e.g. PMCAMx-UF; doi:10.5194/acp-12-8663-2012). It may be helpful to cite examples of models that do not include aerosol dynamical processes (such as condensation sinks, growth via coagulation etc.), as well as the few that do. This would provide a more comprehensive overview and further highlight the importance of your study.

Are you certain that your results are representative of all of China? Considering the regional variability mentioned several times in the manuscript, and given that the analysis was performed only for Beijing and Nanjing, I recommend clarifying this point or keep it consistent throughout the manuscript to avoid ambiguity.

Line 69-70: The sentence states that ‘multiple nucleation theories are interrelated and nucleate synergistically in some cases.’ This is an interesting point and if I understand correctly, this concept is also considered in your study, but the statement lacks detail. I recommend either elaborating briefly on which cases you are referring to or adding relevant references to support the statement.

Line 102: What do you mean by the term “episodes”? I recommend defining or specifying these episodes more clearly to avoid ambiguity and improve readability.

Line 160: The sentence lists the configuration mechanisms used for the gas-phase and aerosol modules but does not provide any details or references in this context for the readers. I suggest briefly elaborating on these mechanisms in one sentence to improve clarity and context.

Line 53 (minor language/grammar suggestions for clarity): The sentence is a bit unclear. For example, the words like “that” and “and” seems to be misplaced here. I suggest revising it to either “in which” or “where” and “that grow into particles…”, for the improved readability.

Line 99: Do you mean “number concentration”?

Line 141 (minor language/grammar suggestions for clarity): The sentence looks incomplete. I suggest to please check and rephrase this statement.

Line 148: Do you mean “thermodynamic theory”?

Figure1 (minor suggestion): since the unit (cm-3) is common across all figures (y-axis), I suggest incorporating it directly into the y-axis label and possibly renaming the label for clarity, if possible.

Figure2 (minor suggestion): if possible, please increase the font size and add subplot titles (e.g., “Beijing” and “Nanjing”) for consistency with Fig. 1.

Line 301-303 and Figure 3: In the following lines, you describe morning and evening peaks as well as daytime values. If I understand correctly, these refer to Figure 3. However, the figure is somewhat difficult to follow. First, the color representation for ‘None,’ ‘IMN,’ and ‘DMA’ is not clearly distinguishable, please consider changing the colors, making them darker, or increasing the line width. Second, I suggest adding background shading to highlight daytime and nighttime periods, which would make the figure easier to interpret.

Line 306 (minor language/grammar suggestions for clarity): The sentence beginning with “Among of them,…” is not grammatically correct. I suggest changing it to “Among them..".

Line 322: please specify the month also to avoid ambiguity.

Supplement figure S3 (minor suggestion): since this figure presents an important finding of your study, I recommend increasing the font size for better readability, particularly on the x-axis, which is difficult to see.

Line 347: In this sentence you have mentioned “three types of days”, which is then described in the supplement figure. I suggest elaborating on this directly in the text rather than only referring to the supplementary figure, so that readers can understand it without needing to cross-reference.

Figure 5: same as for Figure 3. Please add the background shading to highlight day and night time periods and increase the font size, if possible. Additionally, I suggest incorporating the unit of the nucleation rate (cm-3 s-1) directly into the y-axis label.

Line 388: The sentence appears incomplete “…subsequently lost from the system.” Please explicitly mention the processes responsible for the particle removal from the system to clarify the statement.

Line 398: Do you mean “multiple nucleation schemes”?

Line 415-417: This statement repeats the content from lines 403-405. Please consider removing or rephrasing to avoid redundancy.

Particle number concentrations, as computed by the available parametrization scheme for nucleation within the CMAQ model, did not agree well with observations (in China), and the authors have incorporated few other schemes and conducted simulations. Along with few individual schemes, numerical experiments combining few schemes together, have also been carried out. The Paper suggests enhanced capability of the model with the implemented schemes.

Overall manuscript is a significant advancement and the discussions are clear. The manuscript is recommended for publication in GMD. The following comments are provided for authors to consider during the revision process.

l.81: “WRF-Chem proves that HIO3 nucleation is the main way in future”. This is not very clear. Review and reframe this discussion.

l.97-98: The approach SumBTD and SumID are not clear to me. I did not find much description of these approaches. How do you combine several options of nucleation together? How do you decide which of the options should be combined like in case of BTD or in case of ID, instead of other possible combinations?