Dear Authors,

Please revise your reply document to the original reviewer comments that reflects where (page and line numbers) and how exactly manuscript revisions were made to address each point made by the reviewers. When the authors use general statements such as "We agree with referee’s viewpoint and will add some discussion into the revised manuscript," this is NOT helpful to the Editor or the reviewers' re-examination the revised manuscript.

Please make this change to the reply document and resubmit. I will certainly handle this right away upon submission to make a decision about the manuscript. I hope the authors understand the nature of my request.

Most sincerely, Jason Surratt

Dear Authors,

After my careful re-read of the revised manuscript and inspection of your replies to the reviewer comments, I have decided to accept this manuscript with minor revisions noted. I will not send this back for re-review, but this will be re-reviewed by me before full publication in ACP is considered. I kindly request that the authors carefully address these remaining comments below:

1.) Extractions and HULIS preparations:

Like Reviewer 2 and 3 stated, I still have concerns with acidifying the water extracts before SPE separation. The reason for this concern is if the acidity of the extract is too high in the presence of water you will likely induce acid-catalyzed hydrolysis of certain compounds such as hydroperoxides or even catalyze further reactions that produce lower-volatilty OA than originally present in the original aerosol sample. Shouldn't the authors more clearly state that based on the current set of measurements that this can't be ruled out? Basically, at least directly acknowledge the limitations of the current work. I feel this limitation is weakly stressed in the revised text.

Related to this, the authors should be aware that I think the statement lines 120-122 "It should be noted here that HULIS extracted in this work refers to part of the WSOCs that are hydropobic" is unlcear. Should one really say ".....that are partly hydrophobic in character." They wouldn't be in the water extract if they were completely hydrophobic, right? I can see potential readers of your article being confused by this wording.

Since the extraction is very specific to water, for wording like on line 155 "HULIS samples," I would be clearer here and throughout the remainder of the text that this is the "water-soluble HULIS fraction." Please change this so readers don't get confused that you mean the entire fraction of HULIS. I agree with reviewer 3's concerns on the extraction issue.

2.) One point I want to make after re-reading this manuscript. The authors assume that ELVOCs explain the volatility behavior of the water-soluble fraction of HULIS discussed throughout the manuscript. However, it is unclear to me what chemical data exists at the molecular level to support this statement. The water-soluble fraction can include may compounds resulting from heterogeneous reactions (e.g., acid-catalyzed ring-opening reactions of epoxides, like IEPOX), or other processes. I suggest that more care be taken here. Can the authors at least add a statement clarifying this. All of the pathways you describe could tentatively explain these compounds and I don't think the chemical data are strong enough to emphasize one over any others. As of now, all are tentative proposals.

3.) Revised line 151 stating "we totally analyzer 8 samples":

Dont' the authors mean to say:

"we analyzed a total of 8 samples collected during both winter and summer,"

or do they mean to say 4 total in summer and 4 total in winter? This is unclear from the revised text added to the manuscript.

4.) Revised Lines 155-156:

This is a poorly worded sentence. Can the authors revise this to something like:

"Of the 8 samples analyzed, we selected only 4 of the samples representing different PM concentrations to represent the the ranging types of HULIS samples collected at the SORPES station."

The last part of this sentence "and made the argument clear..." seems to be an incomplete sentence. Please correct this.

5.) Revised Line 276:

Change "Organic matters, ..." to "Organic material, ...."

6.) Revised Line 153 stating "(figures not shown):

Can't the authors add the figures to the SI section? I think interested readers may want to see these details.

Thanks so much,

Jason Surratt

I thank the authors for carefully addressing the last comments. I gladly accept this nice study for publication in Atmospheric Chemistry & Physics. Congratulations!

Most sincerely, Jason Surratt