Dear Authors,
Thank you for your attention to the reviewer’s comments. After careful consideration of your responses and the revised manuscript I have determined that additional revisions are required. Please see below.
1) I agree with Referee 2 that further details are required regarding the analytical procedure and that further explanation for the low concentrations needs to be provide. The addition of the text regarding sample storage is good, however a few more details are required. How long were the samples typically frozen before analysis? Additionally sonication can create reactive oxygen species (e.g., Miljevic et al., 2014) and degrade organic compounds. Was this investigated? Does this have any influence on the low concentrations (relative to other polluted areas) observed?

Additionally, I agree with Referee 2 that there needs to be more discussion about possible reasons for the low concentrations, particularly for oxalate and MSA.

2) I agree with Referee 1’s that the fact that the MSA PMF results had 0% from sea salt needs to be discussed in more detail. In particular, the idea of fresh vs processed sea salt should be explored in the manuscript, not just in the response to referee comments.

3) I agree with Referee 2’s second comment that the citation of Kondo et al (2011) is not warranted in this location (line 52-53 of track changes version). The sentence is specifically discussing organic acids, not organic aerosol more generally. While Kondo et al (2011) describe organic aerosol, the manuscript does not include organic acids. I believe this is the case for several of the references provided for this opening sentence.

4) I agree with Referee 1’s comment 8 that the long list of measurements in other locations is not needed. It is difficult to read, particularly when measurements from various environments are compared (i.e. Arctic) where one would expect extremely different concentrations. It is hard for the reader to judge if concentrations are truly similar or not. I recommend only including the references to similar environments in the main text and moving additional locations to the SI. It would also be useful to report the concentrations in the same units (ng/m3 or ug/m3) for a given acid as this would aid in quick comparison.

5) There are several instances where the strength of the wording needs to be adjusted. For instance, line 666-667 (track changes) “… Translation period indicate that photooxidation…” I think “suggests” is a better word than “indicates” since this is based largely on correlation not on a complete oxidative analysis. The use of “indicate” is also perhaps too strong on line 666. Similarly in the abstract (42-43), it is more appropriate to say that the results are consistent with gas-to-particle conversion rather than “… gas-to-particle conversion largely explained …” That would require measurements of the gases. There may be other instances as well.

Miljevic, B., Hedayat, F., Stevanovic, S., Fairfull-Smith, K. E., Bottle, S. E. and Ristovski, Z. D.: To Sonicate or not to Sonicate PM Filters: Reactive Oxygen Species Generation Upon Ultrasonic Irradiation, Aerosol Sci. Technol., 48(12), 1276–1284, doi:10.1080/02786826.2014.981330, 2014.

Congratulations.