According to the reviewers of the revised version, the manuscript has been greatly improved. However, some comments from Referee #4 still need to be addressed. I ask the authors to do so.

Dear Authors, I greatly appreciate the effort you made to improve the manuscript. Please consider the following additional comments:

Response to Comment 5, from referee #4: “In fact, the first comment on the number of motor vehicles in Chengdu appeared in the introduction section, and we provided necessary references, i.e. https://www.mps.gov.cn/n2254098/n4904352/c9244719/content.html (Line 94)”.
The given reference is not in English. Please provide a reference that is understandable to all readers of ACP.

Comments 6 and 10, from referee #4.
Please include the response to these comments in the text in order to clarify the issue for other readers.

Comment 12, from referee #4: “In section 3.4 source apportionments, the sources profiles of each factor should be given, and related references should be cited to support the source apportionment results.”
I agree that the source profiles can be described in the supplemental material document. However, the references to support the association of a source to each profile are still missing.

In addition, just after submitting my decision regarding the previous version of the manuscript, I received an additional report from an anonymous referee, which I am copying below. Although their comments are minor, I think that they can further improve the manuscript. Hence, I ask you to consider them too.

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In this study, the authors synthesized multiple methods to study the characteristics, sources and formation mechanisms of atmospheric PM2.5 pollution in Chengdu. They captured two typical pollution processes and conducted in-depth analysis of their formation mechanisms, and the results can be used as a reference for local pollution reduction. Compared to previous studies on this city, the research methods and results in this study have a certain degree of innovation. In addition, after carefully reading the first round of review comments and the authors' responses, I believe that the authors responded to the comments with high quality and made necessary modifications, which significantly improved the quality of the manuscript. However, there are still some issues that need to be further modified and improved before being considered for acceptance. The detailed comments are as follows.

1. The authors conducted a detailed analysis of the formation mechanism of two haze processes during the observation period. I would like to know if there is any difference in the formation mechanism of winter haze in Chengdu compared to previous studies? Therefore, it is very necessary to compare with previous study results and add relevant discussions.

2. Line 107-108. The authors mentioned that “At the beginning of 2023, Chengdu experienced several severe haze events, during which the observed PM2.5 mass concentration frequently exceeded the CNAAQS.” Please provide more quantitative descriptions about the severity of this pollution, which will help readers understand the necessity of this study.

3. Line 172. The numbers of single particles analyzed during the four periods were 1325, 1159, 995 and 1870, respectively. I want to know if these analyzed particles are representative? Especially in the third period, the number of particles is less than 1000. This is crucial for the feasibility of the study results.

4. Line 252-253. “This inevitably leads to a the difference in the formation mechanism of air pollution in these two regions in China (Wang et al., 2021)” Why?

5. Line 396-399. The authors provided a detailed explanation for the synchronous increase of T and RH during the haze period in this study. They believe that the elevated RH caused an increase in T. I am curious why a similar phenomenon did not occur in Beijing, where RH increased but the T decreased.

6. Fig. 9/Line 500-503. What are the potential effects of changes in the mixed structure of soot particles. I suggest the authors supplement necessary discussions.

7. Line 524. Please provide a definition of “primary sources”, which types of sources does it include? The current expression is unclear.

8. Line 551-553. “During the NP-2 period, with the removal by precipitation and strong easterly winds, the contributions of secondary sources and vehicular emissions decreased by 14.3% and 9.6%, respectively”. The significant reduction in secondary sources is easy to understand as they are hygroscopic. Why has the contribution of vehicular emissions also shown a significant decrease? The authors mentioned earlier that the main emission species of vehicular emissions are carbonaceous components, which are weakly hygroscopic or hydrophobic.

9. In addition, some comments lack necessary references, such as Line 95-97. The format of references needs to be unified and standardized.

The authors have properly answered all the comments from the referees and myself.