First high-resolution tropospheric NO<sub>2</sub> observations from the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS)

Xi, Liang; Si, Fuqi; Jiang, Yu; Zhou, Haijin; Zhan, Kai; Chang, Zhen; Qiu, Xiaohan; Yang, Dongshang

doi:https://doi.org/10.5194/amt-14-435-2021

Articles | Volume 14, issue 1

https://doi.org/10.5194/amt-14-435-2021

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

https://doi.org/10.5194/amt-14-435-2021

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

Articles | Volume 14, issue 1

Research article

|

21 Jan 2021

Research article |

| 21 Jan 2021

First high-resolution tropospheric NO₂ observations from the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS)

Liang Xi, Fuqi Si, Yu Jiang, Haijin Zhou, Kai Zhan, Zhen Chang, Xiaohan Qiu, and Dongshang Yang

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Final revised paper (published on 21 Jan 2021)
Preprint (discussion started on 24 Jul 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of amt-2020-225', Anonymous Referee #1, 24 Aug 2020
- AC1: 'Authors’ Response to Comments from anonymous referee #1', Liang Xi, 17 Oct 2020
RC2: 'referee comment on Xi et al 2020 (AMT 2020-225)', Anonymous Referee #2, 07 Sep 2020
- AC2: 'Authors’ Response to Comments from anonymous referee #2', Liang Xi, 17 Oct 2020

Peer-review completion

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

AR by Liang Xi on behalf of the Authors (19 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Oct 2020) by Andreas Richter

RR by Anonymous Referee #2 (02 Nov 2020)

RR by Anonymous Referee #1 (09 Nov 2020)

Suggestions for revision or reasons for rejection

Overall, this manuscript has expanded upon details as asked by the initial review, however there are still some lingering issues that need addressing or correction.

Line 133: Can the authors quantify in the text the radiance threshold applied?

Equation 1 is valid for a total VCD, but not tropospheric VCD as is referred to below this equation. .The stratospheric slant column must also be subtracted from the dSCD. In lines Line 167-170, it is stated that the stratospheric column cancels out during flight from the reference but in the comment back to the reviewers it was quantified as a difference up to 8e14 due to the changes in the slant path through the atmosphere, which is not stated in the text. This is an impact and should either be added to this product or by quantified in the error estimate. It is a change of 23% over the time period of the flight...

Line 195: State the range of AOD measurements from MODIS for this flight day.

Line 228: Inconsistencies are expected because one is radiance and the other is surface reflectance. They aren’t the same thing thought they should be similar in spatial pattern. I don’t see differences that would be caused by time differences with how it is displayed here. The one detail that does stick out though is that roadway isn’t visible in the radiance measurements even though UVHIS should be higher resolution than Landsat, so can this be explained just by the color bar range choice? Perhaps but the unweighted averaging within the grid as discussed in Section 4.4? It would be nice to have a sentence or two about this.

Line 278: The authors refer to this ‘weaker’ plume, but it has a higher column density than the last described plume.

Is the noise in Figure 11 primarily attributable to surface reflectivity?

Line 297: This is not correct. Areas with NO2 sources can vary dramatically with time. This is a sample size of 2. Emissions from sources aren’t always constant and their footprints can change dramatically due to meteorology as well. In the case of region B, the variability is almost just as large as it is in region a (maybe even more so). The only consistent region is region C.

Line 315: The authors refer to AMF of 2 and AMF of 1.8 for the reference in the same sentence for the reference. This is confusing. I think we need the AMF for TROPOMI in this case to convert 1e15 VCD to its SCD then divide by the AMF from UVHIS.

Line 365: This comment is in relation to the low bias by UVHIS and high bias by mobile DOAS. It seems that the mobile DOAS would probably be more sensitive to near surface pollution than the aircraft. Is the assumption of the a priori profile a reason for the aircraft being lower than the mobile DOAS and is there an optimal profile between the two that would result in the two being closer to 1:1. I am not suggesting to redo all work with a new a priori but perhaps doing the sensitivity test like was done on the airborne work on the mobile DOAS and see if that is a plausible cause for the biases. Then reflect on that in the text.

Last sentence in Section 6: We haven’t been given reason to believe that the spatial footprint of the mobile DOAS is smaller than the UVHIS pixels. Therefore, this sentence is not a valid reason for these results. The above comment seems more plausible.

Line 20 + final paragraph in Section 6: It is nice to see this improvement in the correlation between Fig 14 a and b. Is the correlation different because of the time difference between measurements or because of the location near the steel factory? It seems more likely to focus on is the difference in time between measurements in the text rather than focusing on the location near the steel plant. This should be detailed in the caption of Figure 14 as well.

Editorial Comments
Title has a misspelled word: Imaing = imaging

Line 44: Change ‘lower’ to ‘coarser’

Delete Lines 120-122. These details are on the next page and fit better there.

Line 215: Delete Other RTM parameters used in the AMF calculations are also provided in Fig. 7. Because there are no other parameters shown that I can see.

Line 236: ‘estimated’ PBL height.
Should section 4.4 go before 4.3 or even before 4.1 because geolocation and other steps would have to be performed before AMF analysis to link it to surface reflectivity and other attitude parameters?

Line 264: refer to Figure 10.

Line 310: the mobile DOAS system hasn’t been introduced yet so it seems inappropriate to bring up here.

Table 3 and Table 5: In the text, please explain what the intensity offset is.

Figure 4, 10, 12, and 13: Please make the numbers indicating the point sources larger. They’re hard to read.

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ED: Publish subject to minor revisions (review by editor) (13 Nov 2020) by Andreas Richter

Dear Liang Xi,

I have now received the second round of reviews and as you will see, both reviewers have comments and one of them provides a list of detailed suggestions.

In addition to the reviewer's comments, I also have some requests and suggestions:

* in the manuscript, you state in line 289 that "the NO2 sources in Feicheng are mainly related to traffic and concentrated along the S104". I frankly cannot see that in the figure and suggest to remove this statement.

* in the caption of Figure 10, you write "NO2 emission". Please replace by "NOx emission" as emissions are usually in the form of NO, not NO2

* when introducing the car-DOAS measurements, please add that the retrieval window in the UV differs from the one used for the airborne observations

* please add acknowledgements and data sources for TROPOMI and LANDSAT 8 data

* in the introduction, it would be good to also make reference to some other imaging DOAS instruments that have been flown for NO2 measurements:

Lamsal, L. N., S. J. Janz, N. A. Krotkov,K. E. Pickering, R. J. D. Spurr,M. G. Kowalewski, C. P. Loughner,J. H. Crawford, W. H. Swartz, and J. R. Herman (2017), High-resolution NO2 observations from the Airborne Compact Atmospheric Mapper: Retrieval and validation, J. Geophys. Res.Atmos., 122, 1953–1970, doi:10.1002/2016JD025483.

Nowlan, C. R., Liu, X., Leitch, J. W., Chance, K., González Abad, G., Liu, C., Zoogman, P., Cole, J., Delker, T., Good, W., Murcray, F., Ruppert, L., Soo, D., Follette-Cook, M. B., Janz, S. J., Kowalewski, M. G., Loughner, C. P., Pickering, K. E., Herman, J. R., Beaver, M. R., Long, R. W., Szykman, J. J., Judd, L. M., Kelley, P., Luke, W. T., Ren, X., and Al-Saadi, J. A.: Nitrogen dioxide observations from the Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument: Retrieval algorithm and measurements during DISCOVER-AQ Texas 2013, Atmos. Meas. Tech., 9, 2647–2668, https://doi.org/10.5194/amt-9-2647-2016, 2016.

Schönhardt, A., Altube, P., Gerilowski, K., Krautwurst, S., Hartmann, J., Meier, A. C., Richter, A., and Burrows, J. P.: A wide field-of-view imaging DOAS instrument for two-dimensional trace gas mapping from aircraft, Atmos. Meas. Tech., 8, 5113-5131, doi:10.5194/amt-8-5113-2015, 2015.

General, S., Pöhler, D., Sihler, H., Bobrowski, N., Frieß, U., Zielcke, J., Horbanski, M., Shepson, P. B., Stirm, B. H., Simpson, W. R., Weber, K., Fischer, C. and Platt, U.: The Heidelberg Airborne Imaging DOAS Instrument (HAIDI) – a novel imaging DOAS device for 2-D and 3-D imaging of trace gases and aerosols, Atmos. Meas. Tech., 7(10), 3459–3485, doi:10.5194/amt-7-3459-2014, 2014.

As there still are a large number of small grammatical problems in the text, it would be good to give it another round of proofreading.

Please consider all comments and suggestions when preparing a revised version of your manuscript.

Best regards,

Andreas Richter

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AR by Liang Xi on behalf of the Authors (20 Nov 2020)

ED: Publish as is (27 Nov 2020) by Andreas Richter

AR by Liang Xi on behalf of the Authors (28 Nov 2020) Author's response Manuscript

Post-review adjustments

AA: Author's adjustment | EA: Editor approval

AA by Liang Xi on behalf of the Authors (15 Jan 2021) Author's adjustment Manuscript

EA: Adjustments approved (15 Jan 2021) by Andreas Richter

Short summary

In this paper, we present a novel airborne imaging differential optical absorption spectroscopy (DOAS) instrument: the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS), which is developed for trace gas monitoring and pollution mapping. In the first demonstration flight on 23 June 2018, the UVHIS instrument clearly detected several NO₂ emission plumes transporting from south to north. UVHIS NO₂ vertical columns are well correlated with ground-based mobile DOAS observations.

First high-resolution tropospheric NO2 observations from the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS)

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Interactive discussion

Peer-review completion

Post-review adjustments

First high-resolution tropospheric NO₂ observations from the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS)