Chemical and isotopic composition of secondary organic aerosol generated by <i>α</i>-pinene ozonolysis

Meusinger, Carl; Dusek, Ulrike; King, Stephanie M.; Holzinger, Rupert; Rosenørn, Thomas; Sperlich, Peter; Julien, Maxime; Remaud, Gerald S.; Bilde, Merete; Röckmann, Thomas; Johnson, Matthew S.

doi:https://doi.org/10.5194/acp-17-6373-2017

Articles | Volume 17, issue 10

https://doi.org/10.5194/acp-17-6373-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-17-6373-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 10

Research article

|

29 May 2017

Research article |

| 29 May 2017

Chemical and isotopic composition of secondary organic aerosol generated by α-pinene ozonolysis

Carl Meusinger, Ulrike Dusek, Stephanie M. King, Rupert Holzinger, Thomas Rosenørn, Peter Sperlich, Maxime Julien, Gerald S. Remaud, Merete Bilde, Thomas Röckmann, and Matthew S. Johnson

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Interactive discussion

Status: closed

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

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SC1: 'Some comments on this paper', Satoshi Irei, 24 Feb 2016
- AC1: 'Reply to S. Irei', Carl Meusinger, 02 Aug 2016
RC1: 'Comments', Anonymous Referee #1, 06 Apr 2016
RC2: 'Review of Meusinger et al.', Anonymous Referee #2, 15 Apr 2016
AC2: 'Author's reply to reviewers', Carl Meusinger, 02 Aug 2016

Peer-review completion

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

AR by Carl Meusinger on behalf of the Authors (02 Aug 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Aug 2016) by Maria Cristina Facchini

RR by Anonymous Referee #2 (02 Sep 2016)

RR by Anonymous Referee #1 (12 Sep 2016)

ED: Reconsider after major revisions (13 Sep 2016) by Maria Cristina Facchini

AR by Carl Meusinger on behalf of the Authors (07 Nov 2016) Manuscript

ED: Referee Nomination & Report Request started (11 Nov 2016) by Maria Cristina Facchini

RR by Anonymous Referee #1 (24 Nov 2016)

ED: Reconsider after major revisions (04 Dec 2016) by Maria Cristina Facchini

AR by Carl Meusinger on behalf of the Authors (13 Jan 2017) Manuscript

ED: Referee Nomination & Report Request started (16 Jan 2017) by Maria Cristina Facchini

RR by Anonymous Referee #3 (10 Feb 2017)

Suggestions for revision or reasons for rejection

This paper describes measurements of secondary organic aerosol (SOA) using two techniques – thermal desorption proton transfer reaction mass spectrometry (PTR-MS) and isotope-ratio mass spectrometry (IR-MS) – to better understand key properties of the aerosol, as well as the general processes underlying SOA formation. The authors use a novel approach for examining the source of the isotopic fragmentation, position-specific isotopic analysis (PSIA) of the parent VOC (a-pinene), and the primary conclusion is that carbon-to-carbon isotopic differences in the parent can describe much (if not all) of the observed isotopic fractionation in SOA formation. This is an interesting and novel result, and to my knowledge the first time this effect has been discussed in the context of atmospheric chemistry or SOA; it may be very helpful in the interpretation of data on 13C-ratios of ambient organic aerosol. It is thus certainly an appropriate topic for ACP. Below are comments that need to be addressed prior to publication.

Most importantly, the PTR-MS and IR-MS results seem largely unconnected. In particular, the PTR-MS results are barely referred to in the entire discussion section, which focuses entirely on the isotopic measurements. (The only exception is a brief mention on p. 16, lines 12-14.) Thus, in the paper’s current form, the reason for including the PTR-MS data in this paper is quite unclear. Either the discussion of how the PTR-MS data relate to the IR-MS results needs to be expanded dramatically (i.e., with detailed discussions about how individual ions, or inferred reaction pathways), or else the PTR-MS part of the paper should be left out completely.

Other comments

Throughout: PTR data are described in terms of “ion concentrations”; this is the incorrect term to use, since the mass concentrations (ng/m3) refer to the parent molecule, not the ion.

P. 9, line 12: An introductory sentence on the basic approach for PSIA (13C NMR) would be helpful here. (It’s well described in the SI.)

P. 11, line 18: I assume fragmentation “in the oven” refers to thermal decomposition of the molecules upon heating; this is the same effect as described later (lines 23-28). Probably this sentence should focus on decomposition within the PTR-MS only.

P. 11, line 23-28: This effect has been shown to be important in a couple recent papers (Hilfiker-Lopez et al, 2016 ES&T 50:2200, Isaacman-VanWertz et al. ES&T 50:9952); those should be cited here.

Figure 4 and accompanying text (P. 12, lines 14-21): This argument is not very convincing based on the data presented. The authors argue that these peaks are from the same molecule, but since the mass spectrum is from a complex mixture, it’s not clear why this must be the case. It is mentioned (in the SI only) that the ions exhibit similar thermograms, but these aren’t shown anywhere. To make this argument that the ions are from a single species, these thermograms need to be provided, and also shown to be substantially more similar than most other pairs of ions.

Figure 4: Panel b provides almost no information and should probably be omitted. The very large peaks appear to me to be siloxanes.

Section 3.3: Differences in values need to be discussed relative to the uncertainty/error inherent in the isotopic ratio measurements. Might any of these differences observed be related to limitations on precision/accuracy of the technique?

Figure 6: Panels a and b present results from different back filters. These should be made consistent (ideally both showing B1b and C2b).

Figure 6c: This adds relatively little information in the paper, except for showing that the two techniques (IR-MS and PTR-MS) are qualitatively consistent. This could go in the SI; alternatively, the integrated, calibrated signal could give a “total carbon” measurement, which could help understand why the PTR-MS and SMPS loadings were so different.

P. 13, line 21: The butanol-cyclohexane differences are quite large. The possible reasons for these should be discussed somewhere.

P. 14 line 13 (and P. 5 line 9): It is probably worth mentioning explicitly this is a different “lot” of the same chemical, from the same supplier.

Figure 7: The use of a heat map is unusual here, since there are just ten individual values; the interpolations/extrapolations inherent in a heat map are meaningless in this case.

P. 15, line 18: Is this true even for the Alfa Aesar sample, which has a considerably different isotopic distribution than the others?

P. 16, line 14: Some discussion of oligomerization would be useful here. Oligomerization can bring volatile carbon from the gas phase to the particle phase; and therefore it could offset some of the fractionation arising from fragmentation to small volatile species. Might that be occurring in this case?

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ED: Reconsider after major revisions (10 Feb 2017) by Maria Cristina Facchini

AR by Carl Meusinger on behalf of the Authors (21 Mar 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (22 Mar 2017) by Maria Cristina Facchini

RR by Anonymous Referee #3 (18 Apr 2017)

ED: Publish subject to technical corrections (20 Apr 2017) by Maria Cristina Facchini

AR by Carl Meusinger on behalf of the Authors (28 Apr 2017) Author's response Manuscript

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Short summary

Isotope studies can constrain budgets of secondary organic aerosol (SOA) that is pivotal to air pollution and climate. SOA from α-pinene ozonolysis was found to be enriched in ¹³C relative to the precursor. The observed difference in ¹³C between the gas and particle phases may arise from isotope-dependent changes in branching ratios. Alternatively, some gas-phase products involve carbon atoms from highly enriched and depleted sites, giving a non-kinetic origin to the observed fractionations.