|The paper by Reeves et al. has been significantly improved. The authors have carefully addressed the main issues raised, in my judgement. I feel that the revised paper is a significant contribution to the literature, given the speciated organic nitrate measurements reported here, from isoprene chemistry. The measurements made were difficult, and, with the uncertainties added in the revision, represent useful ambient data.|
The paper could be further improved, if there is one more round of edits by again paying less attention to the tedious details (e.g. telling the reader about all the information that is in W2018) and focusing on what is new. In particular, the Conclusions just repeat what is said in the paper, implying that it wasn’t said well enough in the paper. The Conclusions section is an opportunity to paint the big picture as to – what did we learn that is new? A list of the points made in the paper is relatively dull. It would be better to focus on what new understanding was obtained, and at least equally importantly, what needs to be done next (which is there to some extent). Are there suggestions for improved measurements? Better time resolution? Are there laboratory studies that need to be done? What could be done to better understand the fate of nitrooxy-peroxy radicals, etc. I note that with all those standards, it would be trivial to measure all the hydrolysis rates, and information about hydrolysis lifetimes vs aerosol pH and structure are badly needed. Minor edits I would recommend are listed below, in the order they arose in the paper.
1. Line 123 – We used a chemical…
2. Section 4.1 is not needed, it can be incorporated into the results and discussion, as needed.
3. Line 244 – during the Southern Oxidant…
4. Line 261 – why would that be? Please speculate. Is O3 highest in the high NO2/NO condition, and is OH highest at that time? Perhaps you can examine the product [OH][isoprene]xGamma.
5. Line 402 – are you assuming that all species are mixing with clean air? This is an assumption that cannot be justified for all species equivalently. Some longer-lived species such as propanone nitrate will likely have significant concentrations in the residual layer, and mix down as the BL height grows, leading to overestimation of the dilution in such a case, if you are treating all species the same. This should be discussed wherever you discuss the mixing issue (e.g. line 579, 592).
6. Lines 424 and 425 – this implies that for some days, model and data compare better? If so, say so.
7. Lines 426 and 427 – could there be greater evening production or slower loss?
8. Line 432 – than observed…
9. Line 434 – delete comma after that
10. Line 485- this assumes that transport to the surface is not the rate limiting step for deposition of “sticky” species. If you have reason to believe that, say why.
11. Line 525 (paragraph) – I think it would help the discussion to plot the average measured [NO3][isoprene] in Figure 8.
12. Line 624 – specify the ratio being discussed.
13. Line 638 – comma after 7
14. Line 665 – “Our interpretation is limited by the uncertainties in our measurements” – how so?
15. Figure 3 – The two colors in panel c are hard to distinguish. Could you plot radiation on those plots? It would help the reader with the discussion of daytime v. nighttime sources of propanone nitrate.
16. Figure 4 – I think you need legends in the figure – the colors won’t work well in the published version.
17. Figure 6 – use a color other than yellow?
18. Figure 7 – Why not add a line to panel F that represents the best fit to the data in panel E, for ease of comparison of measured and modelled data (esp. since the scales are different)?
19. S1.1 – state which values for the branching ratio you used for each ISOPOO.
20. S1.2 – first line – it should be nitrooxy, I think.
21. S1.3.1 line 6 and line 13 – you should mention production of the organic hydroperoxides when you mention HO2 as a reactant.
22. In this section you refer to “reaction rates” throughout, when it should say rate constants.