Dear Cristina Carnerero et al.,

Thank you for your revised manuscript. The reviewers had another look at your revisions and answers. Unfortunately, still some major issues need to be clarified before we can proceed. Please have a look at the two reports (see PDF's) and revise your manuscript accordingly.

Kind regards

Paul.

Dear Cristina Carnerero et al,

Thank you for your revised manuscript. Reviewer #2 has further technical comments. In addition, I have further comments that should be carefully taken into account before your manuscript can be accepted for ACP (see detailed comments below). Especially the method part should be revised with the needed care.

Detailed comments (in order of appearance):

Page 2, Line 15: Define UFP here (currently it is defined in line 24 below)
Page 2, Line 31: Volatile -> volatile (to be consistent)
Page 3, line 35: Add “the” before “Madrid metropolitan area”
Page 4, line 29: Add “to” before “study”.
Page 4, line 31: Please define CSIC.
Page 4, 2nd last paragraph: Here and throughout the manuscript, please harmonize the capitalization of instruments and acronyms.
Page 4, line 38: Define CIEMAT.
Page 5, line 5: Define CPC.
Page 5, line 5: As addressed by the reviewers, the comparison between the different instruments is an important statement. Please quantify the agreement (e.g. with statistical values or an extra scatter plot for the supplement). As with every experimental paper, the reader should expect more details on the set-up. Please add all needed details on the operation and set-up (incl. flows, loss estimations, calibration procedures for the each used instrumentation). These are essential experimental details. Please take care in correctly defining the instrumentation (see detailed comments below).
Page 5, line 9: Please define ISCIII (necessarily not known to readers outside of Spain).
Page 5, line 12: Define PTR-ToF-MS. Again, a brief description of one of the key instrumentation should be given here. The reader should follow your paper without consulting extra literature.
Page 5, line 15: “TSI instruments” is not the correct term here (TSI is a company). Replace by a more appropriate word (e.g. “Particle sizing and counting instrumentation”).
Line 17: What do you mean with “Being the inlets individual, each instrument had its own flow rate.”?
Page 5, line 21: Please define “Hy-SMPS”. Maybe rephrase the sentence.
Page 5, line 26: Here and throughout the entire section 2.2, please take care in properly describing the used instrumentation. For example, it should say “The instrument was intercompared with another SMPS (TSI Inc, USA, Model 3776 with a standard XXX DMA) …”. What is a “Hy-CPC”? Is it a company or a special CPC? A CPC usually only counts particles. How was the range 3-1000 nm assured or did you integrate a measured size distribution? Please properly define your used instrumentation!
Page 6, line 3: To be consistent, you could consider using the recently defined acronym for growth rate (GR).
Eq. 3: Please define alpha.
Eq. 5: Please properly define the difference between Dp and Dp’.
Page 6, line 32: Suggest to remove the “s” after balloons.
Page 7, line 12: Add “number” before “particle” (since you show a particle number size distribution)
Page7, line 19: I would suggest to rephrase the beginning of this sentence to: “Since all stations are differently influenced by traffic …” Please specify what you mean with “Otherwise, we would observe significant differences at our stations.” It is not really clear what you mean here.
Figure 1: Please add proper and correct y-axis labels to your figures (incl. the colorbar) and remove your internal acronyms (I assume you show particle diameter).
Figure 8: Why is there only one 25/75th percentile value shown for the urban / Dp>40nm values?
Conclusions: The acronyms ‘CS‘ and ‘CoagS’ are defined again but then not used. I suggest removing them.
Figure S2: Why do you have doubly charged particles also to the left of the main peak at 50nm?

In general, I think you should revise once more if not certain supplementary material should be moved to the main manuscript (e.g. S1). There are a many references to supplementary material inside the text which made me switch back and forth between main manuscript and supplement. It reads not very well if a new section start with referencing to the supplement (see e.g. Sect 3.1).

Please have a thorough additional editorial read of your manuscript and also check for English language and grammar.

Dear Christina Carnerero et al,

Thank you for your revised manuscript. In general, the comments were sufficiently addressed. However, I still see a major issue in the proper usage of English language (e.g. sentences like "Being the inlets individual, each instrument had its own flow rate." do not make any sense). I therefore strongly urge you or one of your co-authors (there seem to be some native speakers) to do one more proper editorial read before it can be finally accepted. Especially revise the grammar and wording of Sect. 2.2. but please don't neglect the rest of the manuscript.

Concerning your whisker plots (Fig 4 and 10), please also add the number of data points for each case.

Thanks and kind regards,

Paul.

Dear Christina Carnerero et al,

Thank you for your revised manuscript. The English language has improved. However, in your revised figures 4 and 10, you now show that you have only a limited amount of data on which your conclusions are based on. A box-and-whisker plot with only three data points is highly questionable. Hence, I would like that you (together with your co-authors) revise your statistical analysis and figures once more. Please add error bars to Fig. 5.

Kind regards

Paul.

Dear Cristina Carnerero et al.,

Thank you for your revisions, which clearly improved the manuscript. I'm pleased to decide that your manuscript is now ready to be published in ACP.

A few more technical corrections should be considered:

- Figure 8: Increase the font size of your subplots (should be approx. the same as the figure caption font size).
- Figure 4: Specify in the caption if the average is a mean or a median. The shading is really difficult to see, maybe increase the contrast or decrease the transparency.
- Figure 6 & 7: The red bullets are rather orange to me.
- Figure 1: Specify the origin of the satellite image and check the rights to publish it.

Thanks and kind regards from Sweden,

Paul.