Traffic and nucleation events as main sources of ultrafine particles in high-insolation developed world cities

Brines, M.; Dall'Osto, M.; Beddows, D. C. S.; Harrison, R. M.; Gómez-Moreno, F.; Núñez, L.; Artíñano, B.; Costabile, F.; Gobbi, G. P.; Salimi, F.; Morawska, L.; Sioutas, C.; Querol, X.

doi:https://doi.org/10.5194/acp-15-5929-2015

Articles | Volume 15, issue 10

https://doi.org/10.5194/acp-15-5929-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

SAPUSS: Solving aerosol problems by using synergistic strategies...

https://doi.org/10.5194/acp-15-5929-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 10

Research article

|

28 May 2015

Research article |

| 28 May 2015

Traffic and nucleation events as main sources of ultrafine particles in high-insolation developed world cities

M. Brines, M. Dall'Osto, D. C. S. Beddows, R. M. Harrison, F. Gómez-Moreno, L. Núñez, B. Artíñano, F. Costabile, G. P. Gobbi, F. Salimi, L. Morawska, C. Sioutas, and X. Querol

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Final revised paper (published on 28 May 2015)
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Preprint (discussion started on 22 Oct 2014)
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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC C9419: 'More detailed evaluation', Anonymous Referee #1, 22 Nov 2014
AC C10118: 'reply to reviewer 1', Mariola Brines, 12 Dec 2014
RC C11017: 'Interactive comment on “Frequency of new particle formation events in the urban Mediterranean climate” by M. Brines et al.', Anonymous Referee #3, 09 Jan 2015
RC C11106: 'Reviewer comment on 'Frequency of new particle formation events in the urban Mediterranean climate'', Anonymous Referee #2, 12 Jan 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Mariola Brines on behalf of the Authors (11 Feb 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Feb 2015) by Roberta Vecchi

RR by Anonymous Referee #3 (09 Mar 2015)

RR by Anonymous Referee #2 (25 Mar 2015)

Suggestions for revision or reasons for rejection

The revised paper has been modified significantly and the authors tried to address reviewers remarks. However, to my opinion not all points were answered and modified in a satisfying way, thus, more works needs to be done.

The re-arrangement of cities is okay to have more statistical significance.
In general, this paper is dealing with a topic: analysis of aerosol number size distributions in cities which became very popular in the last years. Thus, the presentation and simple analysis is not enough for a scientific publication, one also needs a good conclusion and an answer to the question where can the results be used for? This is still a very weak part of the present paper and some more effort should be put into drawing relevant conclusions.

I would also like to see more comparison with other cities. There are many measurements available over the past 20 years and at least some more from other countries should be mentioned.
With some additional work on the points mentioned here the paper might be published in ACP, but first its scientific relevance needs to be stated clearly.

Measurements:
Whats about the humidity in the inlet system? I read in the Brines et al, 2014 paper that no dryer was used, was this the case also here? Was the sheath air dried? I think the standard TSI-systems do not have a dryer included. Particularly under high humidities as they may occur in the Mediterranean the hygroscopic growth could play a significant role and should be discussed in the paper. This is a very crucial point for the data quality and influences all conclusions.

Results:
Traffic cluster: I am not happy with the high number of clusters. For instance the traffic clusters: T1 and T2 look very similar and T3 does not really fit to my opinion. It shows strong indications for nucleation, e.g. has its maximum around noon and the small mean diameter, thus I do not believe that it is related to traffic.
As I already wrote in my first review: In the urban environment it might be hard to distinguish between traffic-induced secondary aerosol formation and new particle formation. In fact, both processes are induced by nucleation, even the precursors like sulfuric acid might be the same. I strongly recommend to read this paper (Uhrner et al., Atmospheric Environment 41 (2007) 7440–7461) which shows nicely how nucleation and growth happen after the tailpipe.

I do not like the answer of the authors in this point where they state that newly formed particles in the exhaust of cars are generally treated as primary. This is not true and it has to be discussed here. There are different mechanisms of new particle formation going on in cities due to the variety of precursor gases and other conditions. But this needs to be discussed and makes such a study in a city more difficult.
I did not get the reason for the Summer background cluster? It is not mentioned in the discussion later, thus: it is not important? Of course in all cities the background my play an important role, but it is also very likely that the background is different. Maybe this is the reason for the high number of clusters? If this is the case, maybe a common data analysis for all cities is not reasonable and should be limited to similar cities only?
New particle formation has been observed in other European cities too with very similar characteristics (e.g. in Leipzig, Germany). You should include such studies into your study. Another hint: Why don’t you separate between weekends and weekdays? I expect a completely different driving behavior and one can probably detect new particle formation much clearer on weekends. Also the distribution of clusters is probably different due to the different traffic behavior.

Page 20, line 12: How can you state that a NPF event is of regional type? This is not possible to my opinion from one measurement site. The contour plots also do not show any growth of particles which could be a hint for a regional event. I think it is very typical for cities that NPF occurs but particles do not show a clear growth (banana-like). If you add some more studies from other cities you can show this.

One hypothesis for the small particles could be also that the particles were formed somewhere else and transported by advection or vertical mixing due to convection. This would explain why they appear at larger diameters and do not show up at the lower end of SMPS. Also here, the investigation of new particle formation on weekends separately could help!

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ED: Reconsider after minor revisions (Editor review) (25 Mar 2015) by Roberta Vecchi

AR by Mariola Brines on behalf of the Authors (26 Apr 2015) Author's response Manuscript

ED: Publish subject to technical corrections (29 Apr 2015) by Roberta Vecchi

AR by Mariola Brines on behalf of the Authors (29 Apr 2015) Manuscript

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