Dear Authors,

Thanks for responding to the reviewers' comments. I have received further comments from reviewer #1. The reviewer noted that the manuscript is improved but still difficult to follow. Please address the comments listed below. Specifically, I also think the role of NOx and NO3 as tracers for HOA and SV-OOA needs to clarified and discussed in more details. Further, moving some minor figures to the SI could improve the readability and clarity of the manuscript.

Best,
Sally

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Further comments from reviewer #1:

1. The manuscript shows that particulate nitrate is enhanced during high PM periods, and attributes this to inorganic nitrate arising from vehicular NOx. The authors do not provide evidence that vehicles are the main source of NOx. There is one plot in the SI that shows a time series of NOx and BC, but otherwise we are left to trust the authors at their word that vehicles are the primary NOx source.
2. Figure 8 uses NOx as a tracer for HOA, and particulate NO3 (correlated with NOx) as a tracer for SV-OOA. While NO3 is typically used as a tracer for SV-OOA, it seems that since one of the central arguments of this manuscript is that vehicle NOx drives the formation of particulate NO3, then NO3 cannot be used as both a vehicle emission tracer and a secondary organic tracer. Perhaps this is evidence that vehicle emissions are rapidly converting to the measured SV-OOA (and that would be an interesting observation), but the authors do not probe further, aside from passing mention in the paragraph from lines 303-321.
3. The manuscript has numerous figures, and several are referred to sparingly in the text (Figs 3 and 4, Fig 5 Na and Ca panels, Fig 11). Having so many figures that are referred to once or twice in the text makes the manuscript difficult to follow.
4. Line 114 - Make sure NR-PM1 is defined prior to this use.
5. Line 134 - define PCA
6. Figure 4 - the colors of the excess ammonium and NO3 traces are not indicated