An evaluation of global organic aerosol schemes using airborne observations

Pai, Sidhant J.; Heald, Colette L.; Pierce, Jeffrey R.; Farina, Salvatore C.; Marais, Eloise A.; Jimenez, Jose L.; Campuzano-Jost, Pedro; Nault, Benjamin A.; Middlebrook, Ann M.; Coe, Hugh; Shilling, John E.; Bahreini, Roya; Dingle, Justin H.; Vu, Kennedy

doi:https://doi.org/10.5194/acp-20-2637-2020

Articles | Volume 20, issue 5

https://doi.org/10.5194/acp-20-2637-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-2637-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 5

Research article

|

04 Mar 2020

Research article |

| 04 Mar 2020

An evaluation of global organic aerosol schemes using airborne observations

Sidhant J. Pai, Colette L. Heald, Jeffrey R. Pierce, Salvatore C. Farina, Eloise A. Marais, Jose L. Jimenez, Pedro Campuzano-Jost, Benjamin A. Nault, Ann M. Middlebrook, Hugh Coe, John E. Shilling, Roya Bahreini, Justin H. Dingle, and Kennedy Vu

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Final revised paper (published on 04 Mar 2020)
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Preprint (discussion started on 06 May 2019)
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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: 'Review of Pai et al, An evaluation of global organic aerosol schemes using airborne observations', Anonymous Referee #1, 30 May 2019
- AC1: 'Response to Anonymous Referee 1', Sidhant Pai, 12 Aug 2019
RC2: 'Review of Pai et al. (2019)', Anonymous Referee #2, 03 Jun 2019
- AC2: 'Response to Anonymous Referee 2', Sidhant Pai, 12 Aug 2019
SC1: 'Short comments of Pai et al. (2019)', Ruqian Miao, 01 Jul 2019
- AC3: 'Response to Comment', Sidhant Pai, 12 Aug 2019

Peer-review completion

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

AR by Sidhant Pai on behalf of the Authors (22 Aug 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Oct 2019) by Neil M. Donahue

RR by Anonymous Referee #1 (22 Oct 2019)

Suggestions for revision or reasons for rejection

The authors have made reasonable efforts to address the concerns of the reviewers, while largely restricting themselves to modifying the paper text rather than performing new analysis. One of their key figures (Fig. 5) is still quite confusing. They have, however, made substantial and valuable additions to the supplementary materials, with a great deal of additional explanation.

The authors’ restricting themselves to only publicly accessible datasets is a somewhat artificial justification for limiting the scope of the study, considering that the author list includes the PIs responsible for the collection of a high fraction of all AMS datasets currently in existence. Of course, the close collaboration of experimental and modeling PIs is necessary even when only publicly available data is used, but it was a little disappointing the authors did not at least include the results of WINTER 2015. Nevertheless, I appreciate that significant effort has gone into the study already and I think it is reasonable for the authors to follow this up in subsequent papers.

Overall I consider the paper a valuable and interesting contribution to the literature and I recommend accepting it subject to the minor comments below.

Minor comments:

Figure 4 shows very large differences between complex and simple schemes in China, and I did not find a dedicated discussion of the reasons for this. Yet the complex and simple schemes are well correlated, and both overestimate OA, in the outflow region (if we assume Korea is the outflow region). At line 626 you might expand on your existing comments, perhaps referring specifically to this and emphasising the large uncertainties associated with IVOCs which some authors suggest could be responsible for more SOA than the Pye and Seinfeld (2010) treatment would suggest – for example, see Zhao et al, Sci Rep 2016.

Figure S1, S4 please say in the caption what the colors represent, or remove them.

Fig 6,10,S2 I still think the authors should use red for sulfate and other colors which do not form part of the AMS scheme, such as purple, for their various organic schemes.

Initially I found the sentence “ISOA and Org-Nit are generated exclusively through the aqueous uptake pathway and do not include any ‘non-aqueous’ OA” confusing, because I read ‘aqueous uptake’ to mean ‘uptake by cloud water, then cloud processing’. And Fisher et al use the term ‘uptake’ but not ‘aqueous uptake’. Of course there is no cloud processing here– the pH of the droplets considered by Marais et al more or less precludes them being activated. But it would be good to make this clearer in the text.

The lab study of Brégonzio-Rozier et al (ACP 2016) cited by Marais et al as a justification for not considering aqueous formation of SOA from isoprene via cloud processing found a very small mass yield of in-cloud isoprene SOA. However, if I interpret their Figure 1 correctly, they did observe a strong enhancement compared to conditions that were first very dry, and then at 80% RH, suggesting that cloud processing could be important compared to ‘aqueous uptake’ in some conditions -I think it’s too early to tell. I realise cloud-processing of SOA is still hugely uncertain and hard to parameterize, but perhaps the authors might briefly mention and discuss the body of research on in-cloud SOA? In-cloud SOA would presumably correlate with aqueous uptake, so I guess it is possible that when the authors find improved performance by replacing VBS with aqueous uptake for isoprene, they are in fact compensating, to some extent, for in-cloud production?

In the SI, it would be good to clarify that the C5-LVOC lumped product, despite its name, still doesn’t partition via the VBS, instead via aqueous uptake. This is clear from the text further down, as C5-LVOC features in the long list of stuff that forms non-volatile aerosols irreversibly, but nevertheless, retaining the name C5-LVOC is potentially confusing.

Would it be possible to include a version of Figure 5 which excludes the upper troposphere as a supplementary figure, so that the surprising classification of the southeastern US as remote can be further clarified, and the different altitudes can be compared?

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RR by Anonymous Referee #2 (14 Nov 2019)

ED: Publish subject to minor revisions (review by editor) (26 Nov 2019) by Neil M. Donahue

AR by Sidhant Pai on behalf of the Authors (05 Dec 2019) Author's response Manuscript

ED: Publish as is (03 Jan 2020) by Neil M. Donahue

AR by Sidhant Pai on behalf of the Authors (12 Jan 2020) Author's response Manuscript

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Short summary

Aerosols in the atmosphere have significant health and climate impacts. Organic aerosol (OA) accounts for a large fraction of the total aerosol burden, but models have historically struggled to accurately simulate it. This study compares two very different OA model schemes and evaluates them against a suite of globally distributed airborne measurements with the goal of providing insight into the strengths and weaknesses of each approach across different environments.