Observing atmospheric formaldehyde (HCHO) from space: validation and
intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B,
OMPS) with SEAC<sup>4</sup>RS aircraft observations over the southeast US

Zhu, Lei; Jacob, Daniel J.; Kim, Patrick S.; Fisher, Jenny A.; Yu, Karen; Travis, Katherine R.; Mickley, Loretta J.; Yantosca, Robert M.; Sulprizio, Melissa P.; De Smedt, Isabelle; González Abad, Gonzalo; Chance, Kelly; Li, Can; Ferrare, Richard; Fried, Alan; Hair, Johnathan W.; Hanisco, Thomas F.; Richter, Dirk; Jo Scarino, Amy; Walega, James; Weibring, Petter; Wolfe, Glenn M.

doi:https://doi.org/10.5194/acp-16-13477-2016

Articles | Volume 16, issue 21

https://doi.org/10.5194/acp-16-13477-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-16-13477-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 21

Research article

|

01 Nov 2016

Research article |

| 01 Nov 2016

Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC⁴RS aircraft observations over the southeast US

Lei Zhu, Daniel J. Jacob, Patrick S. Kim, Jenny A. Fisher, Karen Yu, Katherine R. Travis, Loretta J. Mickley, Robert M. Yantosca, Melissa P. Sulprizio, Isabelle De Smedt, Gonzalo González Abad, Kelly Chance, Can Li, Richard Ferrare, Alan Fried, Johnathan W. Hair, Thomas F. Hanisco, Dirk Richter, Amy Jo Scarino, James Walega, Petter Weibring, and Glenn M. Wolfe

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Final revised paper (published on 01 Nov 2016)
Supplement to the final revised paper
Preprint (discussion started on 14 Mar 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Zhu et al. (2016)', Anonymous Referee #1, 05 Apr 2016
- AC1: 'Responses to Reviewer #1', Lei Zhu, 07 Jul 2016
RC2: 'Review of “Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC4RS aircraft observations over the Southeast US” by Zhu et al.', Anonymous Referee #2, 07 Apr 2016
- AC2: 'Responses to Reviewer #2', Lei Zhu, 07 Jul 2016
RC3: 'Review of Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC4RS aircraft observations over the Southeast US', Anonymous Referee #3, 20 Apr 2016
- AC3: 'Responses to Reviewer #3', Lei Zhu, 07 Jul 2016

Peer-review completion

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

AR by Lei Zhu on behalf of the Authors (07 Jul 2016) Manuscript

ED: Referee Nomination & Report Request started (06 Aug 2016) by Rainer Volkamer

RR by Anonymous Referee #2 (11 Aug 2016)

RR by Anonymous Referee #1 (12 Aug 2016)

Suggestions for revision or reasons for rejection

Second Review of Zhu et al.

Specific issues:

Page 3 Lines 9-10. You imply that direct satellite validation profiles are not useful, as the noise in the satellite data is high. This is not really true is it? One can still average validation profiles coincident with satellite observations, to mitigate for noise in the retrievals.

Page 3, lines 28-29: The gridded HCHO errors on the de Smedt et al (2008) correspond to GOME & SCIAMACHY averages, which have sample less frequently than the sensors in this study. Please give the appropriate errors for OMI, GOME-2 (A/B) and OMPS – as asked for originally.

Page 3, lines 31-32. Why was data only in the range -0.5 to 10 x1016 molecules/cm2 used?

Page 5, lines 6-7. It would be more accurate to say “Diurnal variability in the HCHO columns over this regions is expected from models to be less than 10%, assuming a correctly simulated diurnal photochemical cycle…” (or similar).

Page 5, lines 18-20. Okay, you construct mean HCHO columns to reduce “noise” (here I assume you mean in the retrieval). However, I still think computing the ‘aircraft’ HCHO columns for each flight and their spatial extent, and comparing that to the satellite data that lie within the aircraft footprint, should be a first step. OMI has good coverage, so you should still get a sufficient number of observations to average. Even if the comparison is ‘bad’ as you indicate, it would still be useful to show it maybe in the supplementary materials (& if the approach is poor then it of course adds credibility to your chosen method).

Page 5, lines 20+. The uncertainty in the conversion using the mean HCHO profile has not been quantified. Assuming the mean observed HCHO profile, is a good approach, but it still needs some error associated with it (yes, the error maybe small but it needs to be in the paper). This was asked for in the previous review & should have been included in the revised manuscript, but for some reason the authors have not done it.

Section 4. Again I still think computing consistent AMFs using GEOS-Chem would be a useful exercise and would help to identify and explain the retrieval differences, but it shouldn’t limit publication.

One final point: There are several places were you have written “HCHO columns serve as a useful proxy isoprene emissions” (or similar). It should be something like “our analysis/results show that HCHO columns may serve as a useful proxy isoprene emissions over this region” – although we already knew this based on the works of Palmer et al and Millet et al.!

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ED: Reconsider after minor revisions (Editor review) (01 Sep 2016) by Rainer Volkamer

AR by Lei Zhu on behalf of the Authors (11 Sep 2016) Author's response Manuscript

ED: Publish as is (18 Oct 2016) by Rainer Volkamer

AR by Lei Zhu on behalf of the Authors (18 Oct 2016) Manuscript

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Short summary

HCHO column data are widely used as a proxy for VOCs emissions, but validation of the data has been extremely limited. We use accurate aircraft observations to validate and intercompare 6 HCHO retrievals with GEOS-Chem as the intercomparison platform. Retrievals are interconsistent in spatial variability over the SE US and in daily variability, but are biased low by 20–51 %. Our work supports the use of HCHO column as a quantitative proxy for isoprene emission after correction of the low bias.

Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC4RS aircraft observations over the southeast US

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Interactive discussion

Peer-review completion

Observing atmospheric formaldehyde (HCHO) from space: validation and intercomparison of six retrievals from four satellites (OMI, GOME2A, GOME2B, OMPS) with SEAC⁴RS aircraft observations over the southeast US