Characterization of organic aerosol across the global remote troposphere: a comparison of ATom measurements and global chemistry models

Hodzic, Alma; Campuzano-Jost, Pedro; Bian, Huisheng; Chin, Mian; Colarco, Peter R.; Day, Douglas A.; Froyd, Karl D.; Heinold, Bernd; Jo, Duseong S.; Katich, Joseph M.; Kodros, John K.; Nault, Benjamin A.; Pierce, Jeffrey R.; Ray, Eric; Schacht, Jacob; Schill, Gregory P.; Schroder, Jason C.; Schwarz, Joshua P.; Sueper, Donna T.; Tegen, Ina; Tilmes, Simone; Tsigaridis, Kostas; Yu, Pengfei; Jimenez, Jose L.

doi:https://doi.org/10.5194/acp-20-4607-2020

Articles | Volume 20, issue 8

https://doi.org/10.5194/acp-20-4607-2020

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

https://doi.org/10.5194/acp-20-4607-2020

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

Articles | Volume 20, issue 8

Research article

|

21 Apr 2020

Research article |

| 21 Apr 2020

Characterization of organic aerosol across the global remote troposphere: a comparison of ATom measurements and global chemistry models

Alma Hodzic, Pedro Campuzano-Jost, Huisheng Bian, Mian Chin, Peter R. Colarco, Douglas A. Day, Karl D. Froyd, Bernd Heinold, Duseong S. Jo, Joseph M. Katich, John K. Kodros, Benjamin A. Nault, Jeffrey R. Pierce, Eric Ray, Jacob Schacht, Gregory P. Schill, Jason C. Schroder, Joshua P. Schwarz, Donna T. Sueper, Ina Tegen, Simone Tilmes, Kostas Tsigaridis, Pengfei Yu, and Jose L. Jimenez

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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 Hodzic et al.', Anonymous Referee #1, 09 Oct 2019
- AC1: 'Responses to Reviewer #1', Alma Hodzic, 04 Feb 2020
RC2: 'Review of Hodzic et al.', Anonymous Referee #2, 27 Oct 2019
- AC2: 'Responses to Reviewer #2', Alma Hodzic, 04 Feb 2020
RC3: 'ATom OA Review', Anonymous Referee #3, 14 Nov 2019
- AC3: 'Responses to Reviewer #3', Alma Hodzic, 04 Feb 2020

Peer-review completion

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

AR by Alma Hodzic on behalf of the Authors (04 Feb 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Feb 2020) by Sergey A. Nizkorodov

RR by Anonymous Referee #2 (27 Feb 2020)

Suggestions for revision or reasons for rejection

The authors have done considerably work to address the points raised in review, substantially improving the manuscript. A few points remain to be addressed prior to publication:

1. A2.3: A likely explanation for the overestimate of POA in models (when treated as NV) is that emissions of POA were likely overestimated (i.e. SV emissions reported as POA when estimated under high loading conditions, Robinson et al., 2007), so one possible solution for these models is the need to re-balance this (downgrade POA emissions, increase SV SOA sources). It would be nice to see this history (i.e. the incorrect assumption that emissions were all NV) acknowledged in Section 4.4.

2. A2.5: The updated tables are clearer, but given that these appear in SI, I suggest that the authors include in the text either the standard deviation or range of values averaged to obtain 1.5 and 1.48 in lines 1950 and 1952.

3. A2.5: It remains unclear exactly how equation 1 was applied to the data. I believe that the authors applied the average POA/BC EFs that were discussed in Section 3.2 to ALL data, but the text “an emission ratio appropriate to the airmass origin..” on L2301 seems to suggest that there is some sort of back trajectory to identify the origin of air masses applied to determine the EF. Please clarify this process in the text.

4. A2.5: The authors state that they could not perform a similar analysis on model output to test the approach of equation 1 because they do not have model output for BC from various emission sectors – I presume that what they mean here is that they would need fBB from the model. It seems that the authors could have chosen to output this information as part of the SV-POA simulation that they performed during review process. Given that the authors have not verified their method with model data, they should explicitly acknowledge that the validity of their analysis approach has not been tested with simulated data, and that future work should verify this approach.

5. A2.6: The authors have not sufficiently described the inorganic aerosol simulations in the model description section (2.1), including a description of relevant thermodynamic schemes (highlighting which models did not include nitrate and ammonium) and emissions input and schemes (i.e. sea salt and dust). Without such a description, the results of Section 4.6 should not be included as the reader has not been provided sufficient basis for assessing these schemes.

6. A2.16: Are the authors suggesting that the spatial distribution and observed OA magnitudes are the same between ATom-1 and ATom-2?? Visual inspection of Figure 2 and S1 suggest that these are quite different, and thus the original review comment that Figure S1 should be included in the main text should be re-considered.

7. A2.13: Could the authors explain the logic of why photolytic removal is not included for isoprene-SOA in the text?

8. A2.21: the text “correlates quite well with other gas-phase BB tracers” is not justified in the current manuscript. Please provide plots for the SI, or a reference that shows this (or remove this statement).

9. Line 1934: “documented later” suggests observational confirmation, whereas the POA estimate here is a derived quantity with substantial uncertainties. Recommend this language be modified to “suggested by later analysis..”

10. Line 1965: Please discuss in the text how the new numbers from Andreae 2019 compares to other numbers from literature shown in Table S1

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ED: Publish subject to minor revisions (review by editor) (06 Mar 2020) by Sergey A. Nizkorodov

AR by Alma Hodzic on behalf of the Authors (07 Mar 2020) Author's response Manuscript

ED: Publish as is (15 Mar 2020) by Sergey A. Nizkorodov

AR by Alma Hodzic on behalf of the Authors (16 Mar 2020) Manuscript

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Short summary

Organic aerosol (OA) is a key source of uncertainty in aerosol climate effects. We present the first pole-to-pole OA characterization during the NASA Atmospheric Tomography aircraft mission. OA has a strong seasonal and zonal variability, with the highest levels in summer and over fire-influenced regions and the lowest ones in the southern high latitudes. We show that global models predict the OA distribution well but not the relative contribution of OA emissions vs. chemical production.