A new aerosol flow reactor to study secondary organic aerosol

Pereira, Kelly L.; Rovelli, Grazia; Song, Young C.; Mayhew, Alfred W.; Reid, Jonathan P.; Hamilton, Jacqueline F.

doi:https://doi.org/10.5194/amt-12-4519-2019

Articles | Volume 12, issue 8

https://doi.org/10.5194/amt-12-4519-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-12-4519-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 8

Research article

|

23 Aug 2019

Research article |

| 23 Aug 2019

A new aerosol flow reactor to study secondary organic aerosol

Kelly L. Pereira, Grazia Rovelli, Young C. Song, Alfred W. Mayhew, Jonathan P. Reid, and Jacqueline F. Hamilton

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Final revised paper (published on 23 Aug 2019)
Supplement to the final revised paper
Preprint (discussion started on 07 Feb 2019)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee's report', Anonymous Referee #3, 08 Mar 2019
- AC1: 'Author response', Kelly Pereira, 22 May 2019
RC2: 'Comments on “Novel Aerosol Flow Reactor to Study Secondary Organic Aerosol” by Pereira et al', Anonymous Referee #4, 09 Mar 2019
- AC1: 'Author response', Kelly Pereira, 22 May 2019
RC3: 'Pereira et al. review', Anonymous Referee #1, 13 Mar 2019
- AC1: 'Author response', Kelly Pereira, 22 May 2019

Peer-review completion

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

AR by Kelly Pereira on behalf of the Authors (22 May 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 May 2019) by Mingjin Tang

RR by Anonymous Referee #3 (10 Jun 2019)

RR by Anonymous Referee #1 (15 Jun 2019)

Suggestions for revision or reasons for rejection

In the revised paper, the authors have addressed some of the issues that the reviewers raised. However, I do not think that it is sufficiently improved relative to the AMTD version to be accepted for publication. Neither of my major comments is satisfactorily responded to.

Regarding the UV field, the authors acknowledged that more lamps would greatly help and it would not be difficult to install them. Then the authors should use a design with more lamps as the base CFR design in this study. Or at a minimum, they should clearly acknowledge in the abstract and conclusions that most space in the current CFR design is photochemically dark (“not sufficient to provide uniform light distribution within the reactor” in the revised paper is misleading as a uniform light distribution in reactors is virtually impossible), propose a better lamp layout and discuss its possible improvements compared to the current design. In my comments to the AMTD paper, I already stated that the CFR in the current design is not really an effective setup producing large quantities of SOA. Even under atmospherically irrelevant conditions, PAM and PEAR can still be generally more efficient in producing SOA because their effective photochemically active volumes are larger than that of the CFR. Also, it has been shown that the condensation of gases on OA particles may be kinetically limited in OFRs, but this is not important unless the condensation sink is very low (Palm et al., 2016; Ahlberg et al., 2017; Eluri et al., 2018). A longer residence time of 25 min in the CFR cannot make a major difference in the quantity of SOA produced. Thus, the arguments that the authors used to show that the CFR has advantages in producing large quantities of SOA are not valid.

The authors acknowledged that they did not aim to use the CFR to produce atmospherically relevant SOA. Then the scientific significance of this paper is seriously limited. While I agree that the relationship between the chemical composition and physicochemical properties of SOA is not affected by its atmospheric relevance, a reactor that can only explore this relationship in a part of the composition/property space that is far from atmospherically relevance has very limited usefulness. As I said in my review of the AMTD paper, the conditions under which the CFR were run were remarkably different (orders of magnitude away) from the atmospherically relevant conditions. To my knowledge, there is not any easy solution that can efficiently produce mg of SOA that can serve as ambient SOA surrogate. If the authors can use the CFR to achieve this goal, that will be a real novelty and should be detailed in this paper. Otherwise, the authors should clearly acknowledge that the CFR is unable to produce ambient surrogate SOA when producing SOA in large quantities.

Other comments:
Response 1 to Referee 4: if experiments are run with ppmv of precursors, they are very likely atmospherically irrelevant. Then the only goal of these experiments is to make as much SOA as possible. It is unclear to me why “memory effects” should be considered as a problem. In other words, I am wondering why “memory effects” should be taken more seriously than atmospheric irrelevance, as to me both are types of inabilities to explore certain parts of SOA chemical composition space. Besides, I do not think that a custom-built PAM itself is expensive.

Response to my “Table 1” comment: I do not understand this response. If the authors wished to conduct low-NOx experiments, simply injecting no NO would work, since NO is not necessary for photochemical production of OH in the CFR.

References:
Ahlberg, E., Falk, J., Eriksson, A., Holst, T., Brune, W. H., Kristensson, A., Roldin, P. and Svenningsson, B.: Secondary organic aerosol from VOC mixtures in an oxidation flow reactor, Atmos. Environ., 161, 210–220, doi:10.1016/j.atmosenv.2017.05.005, 2017.
Eluri, S., Cappa, C. D., Friedman, B., Farmer, D. K. and Jathar, S. H.: Modeling the formation and composition of secondary organic aerosol from diesel exhaust using parameterized and semi-explicit chemistry and thermodynamic models, Atmos. Chem. Phys., 18(19), 13813–13838, doi:10.5194/acp-18-13813-2018, 2018.
Palm, B. B., Campuzano-Jost, P., Ortega, A. M., Day, D. A., Kaser, L., Jud, W., Karl, T., Hansel, A., Hunter, J. F., Cross, E. S., Kroll, J. H., Peng, Z., Brune, W. H. and Jimenez, J. L.: In situ secondary organic aerosol formation from ambient pine forest air using an oxidation flow reactor, Atmos. Chem. Phys., 16(5), 2943–2970, doi:10.5194/acp-16-2943-2016, 2016.

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ED: Reconsider after major revisions (16 Jun 2019) by Mingjin Tang

AR by Kelly Pereira on behalf of the Authors (23 Jul 2019) Author's response Manuscript

ED: Publish as is (23 Jul 2019) by Mingjin Tang

Short summary

We present the design and operation of a newly built continuous-flow reactor (CFR), which can be used as a tool to gain considerable insights into the composition and physical state of secondary organic aerosol (SOA). The CFR was used to generate large quantities of SOA mass, allowing the use of highly accurate techniques that are not usually accessible. We demonstrate how this unique approach can be used to investigate the relationship between SOA formation and physiochemical properties.