A chamber study of the influence of boreal BVOC emissions  and sulfuric acid on  nanoparticle formation rates  at ambient concentrations

Dal Maso, M.; Liao, L.; Wildt, J.; Kiendler-Scharr, A.; Kleist, E.; Tillmann, R.; Sipilä, M.; Hakala, J.; Lehtipalo, K.; Ehn, M.; Kerminen, V.-M.; Kulmala, M.; Worsnop, D.; Mentel, T.

doi:https://doi.org/10.5194/acp-16-1955-2016

Articles | Volume 16, issue 4

https://doi.org/10.5194/acp-16-1955-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

The Pan European Gas-Aerosols Climate Interaction Study...

https://doi.org/10.5194/acp-16-1955-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 4

Research article

|

22 Feb 2016

Research article |

| 22 Feb 2016

A chamber study of the influence of boreal BVOC emissions and sulfuric acid on nanoparticle formation rates at ambient concentrations

M. Dal Maso, L. Liao, J. Wildt, A. Kiendler-Scharr, E. Kleist, R. Tillmann, M. Sipilä, J. Hakala, K. Lehtipalo, M. Ehn, V.-M. Kerminen, M. Kulmala, D. Worsnop, and T. Mentel

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Final revised paper (published on 22 Feb 2016)
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Preprint (discussion started on 11 Dec 2014)

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Status: closed

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

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RC C11883: 'Comments', Anonymous Referee #1, 05 Feb 2015
RC C11910: 'reviewer report', Anonymous Referee #2, 05 Feb 2015
AC C13027: 'Reply to reviewers comments', Miikka Dal Maso, 22 Apr 2015

Peer-review completion

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

AR by Miikka Dal Maso on behalf of the Authors (06 Jul 2015) Author's response

ED: Referee Nomination & Report Request started (20 Jul 2015) by Nikolaos Mihalopoulos

RR by Anonymous Referee #2 (01 Aug 2015)

RR by Anonymous Referee #3 (14 Sep 2015)

Suggestions for revision or reasons for rejection

The authors describe the results of a laboratory study focusing on the formation of new particles during the irradiation of mixtures of biogenic vapors and sulphur dioxide. The main strengths of the work is the use of plant emissions instead of just one or two biogenic hydrocarbons, the measurements of sulphuric acid concentrations, and the detection of very small particles (down to 1.6 nm) with a PSM. However, the main result of the study (the dependence of the new particle formation rate on the biogenic VOC emission rate and not on the corresponding concentration) is puzzling and its extrapolation to the atmosphere through a simple model problematic. These major issues and a number of minor ones are discussed below.

Experimental design: The design of the experiments appears to be weak. One of the most important reactants in the system (sulphur dioxide) was not controlled but it was due to impurities. This raises the possibility that other “impurities” may be responsible for the counterintuitive results. For example, small concentrations of amines have been shown by some of the authors to enhance particle formation rates by several orders of magnitude. Could other emissions by the plants or soil be responsible for the difficult to explain findings of the study?

Extrapolation to ambient conditions. Even if the proposed parameterization is applicable to the experimental set-up used by the authors, its use for atmospheric simulations is clearly problematic. The actual nucleation rate in the atmosphere will not be proportional to the biogenic VOC emission rate, but rather to the corresponding VOC concentrations. As a result it will be affected by atmospheric mixing, availability of oxidants, sunlight intensity, the condensation sink because these affect the relationship between emission rates and concentrations of the species participating in nucleation. I strongly disagree with the suggestion that equations 11 or 12 can be used in atmospheric models. This section should probably be deleted as it is not essential for the rest of the paper and its conclusions.

Discrepancies between a-pinene and full plant chamber experiments. The differences in the results of the experiments with a-pinene from the rest are also puzzling. They do not support the major conclusion of the paper (given the atmospheric abundance and reactivity of a-pinene). They also appear to be inconsistent with the existence of significant amounts of ELVOCs in the a-pinene SOA reported by some of the authors. It is difficult to believe that the organic products of the other monoterpenes would be that much more efficient in forming new particles compared to a-pinene. These results also appear to contradict the conclusion of Ehn et al. (Nature, 2014) that the a-pinene ELVOC products “can enhance, or even dominate, the formation and growth of aerosol particles over forested regions”.

Mixing scales of reaction chamber. One of the potential explanations of the counter-intuitive results of the study is that the reaction chamber is not well mixed and that particle formation takes place mainly near the entrance of the feed streams. Have the authors explored the corresponding mixing dynamics and the spatial homogeneity of particle formation in their reactor? Particle and vapor measurements next to the feed entrances of the reactor would help.

Uncertainty analysis. The authors argue that the uncertainty in the measurements is the cause of the lack of correlation between the expressions based on concentrations and those on fluxes. However, they do not actually show this. This detailed uncertainty calculation is necessary to support this very important argument.

Additional information. A table with the experimental information including concentrations and emission rates of VOCs, OH concentrations, condensational sink during nucleation, etc. for each experiment is needed. There should also be some discussion for the relevance of these conditions (e.g., especially OH and condensational sink) for the atmosphere. This is critical for a parameterization based on fluxes that bypasses these important variables.

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ED: Reconsider after major revisions (22 Sep 2015) by Nikolaos Mihalopoulos

AR by Miikka Dal Maso on behalf of the Authors (03 Nov 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Nov 2015) by Nikolaos Mihalopoulos

RR by Anonymous Referee #3 (08 Dec 2015)

ED: Reconsider after minor revisions (Editor review) (21 Dec 2015) by Nikolaos Mihalopoulos

AR by Miikka Dal Maso on behalf of the Authors (31 Dec 2015) Author's response Manuscript

ED: Publish as is (14 Jan 2016) by Nikolaos Mihalopoulos

AR by Miikka Dal Maso on behalf of the Authors (24 Jan 2016) Author's response Manuscript

Short summary

In this paper, we present the first direct laboratory observations of nanoparticle formation from sulfuric acid and realistic BVOC precursor vapour mixtures performed at atmospherically relevant concentration levels. We found that the formation rate was proportional to the product of sulphuric acid and biogenic VOC emission strength, and that the formation rates were consistent with a mechanism in which nucleating BVOC oxidation products are rapidly formed and activate with sulfuric acid.