Dear authors,

Thank you for your detailed response to the reviewers comments. Reviewer 2 has provided further comments which I copied below. Once these comments are fully addressed, the manuscript can be accepted for publication in ACP.

Best,
Sally

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Reviewer 2 comments

I appreciate the efforts from the authors to address my previous comments. Given the recommendation of the other reviewer and the authors highlighting the value of continuous, multi-site study in New and Old Delhi, I am fine with considering the paper as a research article. There are however still deficiencies that need to be addressed before acceptance:

- Indicate the inlet humidity after use of the drier (and was it a nafion drier or a diffusion drier, etc.)
- My question related to the high Q/Qexp for some m/z’s isn’t answered. So what does it mean that some of the key fragments have very large Q/Qexp even if the overall Q/Qexp is not too high? Is a value of 300 not high enough to be of concern?! If the overall Q/Qexp is acceptable, and m/z-dependent Q/Qexp is not going to be discussed, please remove the plots.
- Figure S4. Change “Birmingham PM2.5” to “Gravimetric PM2.5” to be consistent with the text
- By “6 hourly gravimetric PM2.5 mass” do you mean 6-hr filters? As written it seems 6 of 1-hr filters, but the plots have more than 6 filter values, so this needs to be clarified.
- Figure S6 indicates anions were measured by ICP-MS. I don’t think that’s correct. Do the authors mean IC?! Again, remove the reference to Birmingham.
- Figure 4. Factor nHOA is used in Fig. 4 while NHOA is used in Table S4. Use them consistently please. Also, Figure 4 caption need to have a similar description to what’s included for Table S4.

Dear authors,

Thank you for your response to the comments by Reviewer 2. I think all the comments have been addressed but some additional info and explanation regarding the Q/Qexp question would be useful. Specifically, as the reviewer noted, some individual m/z have very high Q/Qexp, up to 300, but the overall Q/Qexp is only around 5. It is unclear why this is the case. It appears that the individual m/z having high Q/Qexp are HOA type ions. Have you checked the input errors for PMF manually, and evaluated if these input errors are too low? If not, it would be useful to double check the errors of these m/z manually.

All these info would be useful for the readers to know to better understand how the PMF solution was obtained. Please explain these observations (very high Q/Qexp for some m/z, but an overall Q/Qexp of around 5), you can keep Figures S10 and S11 in the SI, and add the explanations to the figure captions.

Best,
Sally