The manuscript by Yu et al. presented high temporal resolution aerosol ON measurements and various source markers in urban Shanghai during the fall-winter period of 2021. The authors used the PMF model to identify up to 18 sources or formation processes of aerosol ON. Despite the potential limitations of the PMF predictions, the results obtained may provide valuable insights into the origins and formation processes of ON aerosols in Shanghai and serve as valuable references for future aerosol ON research. Overall, the manuscript is well-structured and well-written. I recommend that this paper could be published in Atmospheric Chemistry and Physics once the authors address the following minor comments.

Major comments:

The author used the PMF model to identify up to 18 contributors of ON, which is very impressive. However, there seem to be some contradictions in the PMF results. 

For example, 1) For factor nitrate formation, ammonium also has a high load. The liquid-phase reaction of ammonium is also one of the very important pathways for the formation of ON. Why is this factor only attributed to nitrate formation here; 

2) For Figures 2 and S3b, the average contribution of traffic emissions to ON was higher from 0:00 to 8:00 (nighttime). Shouldn't the contribution be higher during the morning and evening rush hours? In addition, the average contribution of cooking and oxygenated cooking OA to ON were higher from 18:00 to 22:00. There should also be cooking at noon, and the photochemical reaction should be stronger, leading to more oxygenated cooking OA production; 

3) For Lines 232-233. Based on my understanding, sulfates, isoprene, and α-pinene can all contribute to the formation of ON (e.g., sulfate significantly promotes the formation of organic amine salts; the sulfates and isoprene-related nitrooxy-OS formation exist…), but the authors suggested that they do not contribute to ON. Does this conclusion require more supporting evidence? 

4) For Lines 234-236. Generally, winter pollution should be heavier, as indicated by many previous studies in Shanghai, especially the impact of coal combustion. However, the authors mentioned that the winter case was consistent with the summer case. This doesn't seem to be in line with the actual situation. 

5) For Lines 237-240: Why is there no consistency between the contribution of coal combustion to ON and the contribution of industrial production to ON. This is somewhat confusing. 

Overall, if possible, it is recommended that the author consider the validity of the PMF results more.

More comments:

1.    Lines 35-36 and Lines 235-236: The data seems to be inconsistent, as mentioned in the abstract, the contribution of both coal combustion and vehicle emissions to ON is 21%. The value reported in the main text is 20%.

2.    As reported by the author, the contribution of the primary sources to ON in Shanghai during winter was greater than that of the secondary processes. This seems to be a more important conclusion. However, a significant amount of primary ON emissions are also partitioned to the particulate phase through secondary processes. For example, for organic amines from primary sources, the formation of particulate organic amine salts (they are abundant in fine particulate matter) is closely related to sulfates, nitrates, and organic acids. Therefore, I am still very confused as to why sulfate formation did not contribute to the formation of ON in this study.

Please find my comments in the attached file.