Formation of highly oxygenated organic molecules from aromatic compounds

Molteni, Ugo; Bianchi, Federico; Klein, Felix; El Haddad, Imad; Frege, Carla; Rossi, Michel J.; Dommen, Josef; Baltensperger, Urs

doi:https://doi.org/10.5194/acp-18-1909-2018

Articles | Volume 18, issue 3

https://doi.org/10.5194/acp-18-1909-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-18-1909-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 3

Research article

|

09 Feb 2018

Research article |

| 09 Feb 2018

Formation of highly oxygenated organic molecules from aromatic compounds

Ugo Molteni, Federico Bianchi, Felix Klein, Imad El Haddad, Carla Frege, Michel J. Rossi, Josef Dommen, and Urs Baltensperger

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Final revised paper (published on 09 Feb 2018)
Supplement to the final revised paper
Preprint (discussion started on 23 Dec 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee review', Anonymous Referee #1, 06 Jan 2017
- AC1: 'Author’s response: referee 1', Ugo Molteni, 30 Oct 2017
RC2: 'Review of: Formation of highly oxygenated organic molecules from aromatic compounds. By Molteni, U. et al.', Anonymous Referee #2, 24 Jan 2017
- AC2: 'Author’s response: referee 2', Ugo Molteni, 30 Oct 2017
RC3: 'review', Anonymous Referee #3, 27 Jan 2017
- AC3: 'Author’s response: referee 3', Ugo Molteni, 30 Oct 2017

Peer-review completion

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

AR by Ugo Molteni on behalf of the Authors (30 Oct 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Nov 2017) by Sergey A. Nizkorodov

RR by Anonymous Referee #1 (21 Nov 2017)

RR by Anonymous Referee #2 (23 Nov 2017)

Suggestions for revision or reasons for rejection

The language and the tone of voice have improved significantly from the previous version, which to my mind is in order considering the remaining open questions in the mechanistic details of the aromatic oxidation reactions. Now the results are presented more as an important new observation with less mechanistic details, which I think is adequate for the present. Thus, I can recommend this article for publication after few remaining issues, outlined below, have been duly addressed.
One particular, very recent publication would be good to inspect in this context: S. Wang et al. “Formation of Highly Oxidized Radicals and Multifunctional Products from the Atmospheric Oxidation of Alkylbenzenes” Environ Sci. Technol., 2017, 51, 8442. It is a joint theoretical-experimental description of “HOM” formation from alkylbenzenes. It seems there are some slight discrepancies between these studies, which could be worth mentioning in the discussion.
I am still having a bit hard time in understanding the used OH concentrations, and their influence on the oxidation system. The average OH concentration mentioned is 2 x 10^8 cm-3, and this concentration should be enough for at least 3 OH attacks(!), which seems like a hard thing to accomplish in 20 second reaction time – to still yield a measurable product signal. Then in simulation of Appendix C a value approaching 10^12 cm-3 was used for initial OH concentration, although the main text gives the impression that all of the experiments were with the same photolysis source and power. In addition, it is said in the introduction that the OH reaction with aromatic system leads to “highly reactive products to more oxidants”, and that the high reactivity is due to the non-aromatic double bonds. So it leads me wondering could the 140 ppb of ozone in the tube affect the secondary chemistry, if 3 OH attacks is possible too? Moreover, if 140 ppb O3 was obtained at the setting with a concurrent 2 x 10^8 cm-3 OH production, what was the corresponding value in the experiment with 8 x 10^11 cm-3 initial OH? Could this discussion be made more consistent, and also, somehow clarified?

Referee Report: PDF

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ED: Reconsider after major revisions (24 Nov 2017) by Sergey A. Nizkorodov

AR by Ugo Molteni on behalf of the Authors (19 Dec 2017)

ED: Publish subject to technical corrections (25 Dec 2017) by Sergey A. Nizkorodov

AR by Ugo Molteni on behalf of the Authors (01 Jan 2018) Manuscript

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Short summary

Anthropogenic volatile organic compounds often dominate the urban atmosphere and consist to a large degree of aromatics. These compounds are already known as important precursors for the formation of secondary organic aerosol. This study shows how the oxidation of aromatics with an OH radical leads to subsequent autoxidation chain reactions forming highly oxygenated molecules. We hypothesize that these may contribute substantially to new particle formation events detected in urban areas.