Dear Authors,

I apologize for the delay; I had tried to receive another report from the original Referee #1 but they did not react despite multiple reminder. Instead, I provide several comments below, following your response to their comments, in addition to some other comments.

I am somewhat confused about the timeline of file uploads:
On Aug 14, Referee #2 uploaded a referee report on your revised manuscript that you had submitted on July 27.
On Aug 18, an author’s response file was uploaded as a replacement of the one you had submitted on July 13, as a response to the first round of reviews. Thus, this author’s response only addresses the referee comments on the first version of your manuscript. I could not find any response to the second referee report by Referee #2. If you submitted a revised manuscript and corresponding author’s response files, please check with the editorial office where the files may have been mixed up. – If not, please address the comments by Referee #2 (also attached here), that mostly address the assumptions and analytical methods, in addition to my comments below.

Sincerely
Barbara Ervens

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Editor comments

1) R1.25: Referee #1 had pointed out that changes in the Krevelen diagram may be also caused by mixing of different air masses. While you added the suggested references to Chen et al. (2015) to the method section, this information should be also added on p. 10.

2) R1.19: Referee #1 referred to your previous paper (Hodshire et al., 2019) where ‘a variety of reasons’ are discussed that may affect deltaOA/deltaCO evolution with ageing. I suggest that you include a bit more discussion on these reasons, i.e. similar to the information as included in the SI of your previous paper.

3) R1.39: Referee #1 asked for a detailed discussion to justify the assumption of the initial conditions. Your response is rather vague. I understand that you may not be able to do a quantitative estimate but some more discussion on how this assumption may be qualitatively affect your results should be added.

3) There are several instances, where language is inaccurate or not appropriate. Some examples are included in the following, but please check the complete manuscript for similar expressions. (Please note that the line numbers were cut off in the uploaded manuscript file and only the last two digits are legible. In the following, I refer to these line numbers as they appear in the pdf.)

p. 7, l. 19: ‘for many of the individual metrics’ – be more specific here.

p. 8, l. 43: ‘each variable ages downwind’ should be rephrased

p. 11, l. 54: ‘our fits were made during daytime conditions’ Wouldn’t it be more accurate to say ‘our fits were made FOR daytime conditions’ ?

p. 8, l. 68: ’deltaf60 may be evaporating ‘ should be rephrased

Dear Authors,

many thanks for your careful revision.
Referee #2 made many suggestions to further improve and clarify text throughout the manuscript. Please go through the annotated file to address the comments and implement changes where necessary. After this, I will happy to accept your manuscript for publication in ACP.

Best regards
Barbara

Dear Authors,

Many thanks for carefully responding to the last referee comments. I am happy to accept your manuscript for publication in ACP.

Sincerely
Barbara