Using GECKO-A to derive mechanistic understanding of secondary organic aerosol formation from the ubiquitous but understudied camphene

Afreh, Isaac Kwadjo; Aumont, Bernard; Camredon, Marie; Barsanti, Kelley Claire

doi:https://doi.org/10.5194/acp-21-11467-2021

Articles | Volume 21, issue 14

https://doi.org/10.5194/acp-21-11467-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-11467-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 14

Research article

|

30 Jul 2021

Research article |

| 30 Jul 2021

Using GECKO-A to derive mechanistic understanding of secondary organic aerosol formation from the ubiquitous but understudied camphene

Isaac Kwadjo Afreh, Bernard Aumont, Marie Camredon, and Kelley Claire Barsanti

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Final revised paper (published on 30 Jul 2021)
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Preprint (discussion started on 11 Sep 2020)
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Interactive discussion

Status: closed

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

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RC1: 'Anonymous Review', Anonymous Referee #1, 21 Oct 2020
- AC1: 'Reply on RC1', Isaac Afreh, 04 Feb 2021
RC2: 'Review of Afreh et al., 2020', Anonymous Referee #2, 18 Nov 2020
- AC2: 'Reply on RC2', Isaac Afreh, 04 Feb 2021

Peer-review completion

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

AR by Isaac Afreh on behalf of the Authors (01 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (09 Mar 2021) by Delphine Farmer

RR by Anonymous Referee #1 (24 Mar 2021)

RR by Anonymous Referee #3 (03 Apr 2021)

Suggestions for revision or reasons for rejection

I share the same concern as the Reviewer #2 pointed out that the modeling results are likely not representative of the actual atmosphere scenarios without carefully accounting for the autooxidation chemistry of peroxy radicals and their self/cross-reactions as a widespread source of highly oxidized monomeric and dimeric products (HOMs) that significantly contribute to the SOA formation in the monoterpene system. Recent kinetic studies have demonstrated that this autooxidation pathway could effectively operate and affect the product distributions from the ozonolysis of a-pinene at relatively short RO2 bimolecular lifetimes, e.g., in the presence of ~ppb levels of NO (Lyer et al. Nature Communications 2021). This level of NOx as an upper bound below which the RO2 isomerization outcompete their bimolecular reactions with NO/RO2/HO2 is relevant to the conditions vastly encountered in most regions of the U.S. and also those conditions measured in fire plumes. While I understand, as the authors stated, that full consideration of HOM formation/dimerization is not possible at this time, I suggest, however, a number of sensitivity tests need to be at least performed to evaluate the uncertainties arising from this missing chemical mechanism in the simulations. My understanding that such tests are feasible based on previous published GECKO-A studies, see a couple of examples below.
1. The authors could refer to McVay et al. ACP (2015) in terms of adding the RO2 isomerization channel to the original GECKO mechanism. Recent published RO2 isomerization kinetics in a-pinene ozonolysis (e.g., Kurteń et al., JPCA, 2015; Zhao et al., PNAS, 2018) could be adapted to assess the relevance of the autooxidation chemistry under conditions simulated in this study and how this chemistry could change the product distribution and consequently the SOA yields and composition.
2. La et al. ACP (2016) incorporated a heterogeneous reaction pathway in the GECKO simulations of the SOA formation from photooxidation along-chain alkanes. For this study, it is important to test how the particle-phase dimerization such as the peroxyhemiacetal formation from the poly-peroxides that are largely present in the HOMs molecules (see kinetics in e.g., Bakker-Arkema and Zimemann 2020) could alter the SOA mass and composition.

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ED: Publish subject to minor revisions (review by editor) (14 Apr 2021) by Delphine Farmer

AR by Isaac Afreh on behalf of the Authors (27 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (05 May 2021) by Delphine Farmer

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Short summary

This is the first mechanistic modeling study of secondary organic aerosol (SOA) from the understudied monoterpene, camphene. The semi-explicit chemical model GECKO-A predicted camphene SOA yields that were ~2 times α-pinene. Using 50/50 α-pinene + limonene as a surrogate for camphene increased predicted SOA mass from biomass burning fuels by up to ~100 %. The accurate representation of camphene in air quality models can improve predictions of SOA when camphene is a dominant monoterpene.