Variability of NO<sub>2</sub> concentrations over China and effect on air quality derived from satellite and ground-based observations

Fan, Cheng; Li, Zhengqiang; Li, Ying; Dong, Jiantao; van der A, Ronald; de Leeuw, Gerrit

doi:https://doi.org/10.5194/acp-21-7723-2021

Articles | Volume 21, issue 10

https://doi.org/10.5194/acp-21-7723-2021

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

Special issue:

Satellite and ground-based remote sensing of aerosol optical,...

https://doi.org/10.5194/acp-21-7723-2021

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

Articles | Volume 21, issue 10

Research article

|

20 May 2021

Research article |

| 20 May 2021

Variability of NO₂ concentrations over China and effect on air quality derived from satellite and ground-based observations

Cheng Fan, Zhengqiang Li, Ying Li, Jiantao Dong, Ronald van der A, and Gerrit de Leeuw

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Final revised paper (published on 20 May 2021)
Preprint (discussion started on 05 Nov 2020)

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

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RC1: 'my comments', Anonymous Referee #1, 29 Dec 2020
RC2: 'Review of ACP 2020 1101', Anonymous Referee #2, 02 Jan 2021
AC1: 'Comment on acp-2020-1101', Cheng Fan, 01 Feb 2021

Peer-review completion

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

AR by Cheng Fan on behalf of the Authors (01 Feb 2021) Author's response Author's tracked changes

ED: Referee Nomination & Report Request started (02 Feb 2021) by Stefania Gilardoni

RR by Anonymous Referee #1 (18 Feb 2021)

RR by Anonymous Referee #2 (02 Mar 2021)

Suggestions for revision or reasons for rejection

The authors have made an excellent job both in addressing and replying both reviewers' comments as well as altering their manuscript to now better demonstrate the status of air quality over East China. I highly commend them on that. Having said that, I am still concerned about the presentation of their findings.

1. I would expect to first see the back-in-time discussion for the NO2 levels, i.e. Section 3.1.2, on OMI, and then what happened during 2020 and COVID, by TROPOMI, i.e. Section 3.1.1. It makes more of a natural flow of information this way, especially since you do not have back-in-time analysis for the AQI/surface concentrations.

2. Figure 4 shows OMI NO2 up to and including months of year 2020, these should be excluded since you do not plan to discuss them. Overall the quality of the graph is poor, make sure all labels increase in size, are made bold, and so on.

Furthermore, when a trend is calculated from such a seasonally-varying species as is NO2, the time series has to be de-seasonalised beforehand. This is not explicitly mentioned in the text. I strongly suggest that you first de-seasonalise and then provide trends in the relevant Table.

3. Since in the rest of the text you show weekly timeseries for the AQI/surface concentrations for the COVID weeks, I strongly recommend you also show, in the TROPOMI section, similar timeseries. If not, again your results appear to be "un-connected' i.e. you first have one satellite giving you the 10 year NO2 trend, then another giving you what went on during COVID for the 2020 weeks, then you have surface concentrations of NO2 and other species, plus AQI, only for the COVID 2020 weeks. I am not suggesting that you compare TROPOMI NO2 to the surface concentrations, this task is a paper on its own. You should however show if similar patterns appear. These patterns cannot be seen from Fig. 3 & Fig A1 which are demonstrational only.

Overall, from the time series provided, I note that the AQI is mostly influenced by PM2.5, rather than the variation on NO2.

Technical: throughout the text there are references to a Figure/Table in the supplement, I assume this was a typo error? Figure A1 should be made with a colour bar the reflects differences, i.e. going from blue to white -which means 0- and then to red. Figure A2 is of low quality and should be improved.

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ED: Reconsider after major revisions (03 Mar 2021) by Stefania Gilardoni

AR by Cheng Fan on behalf of the Authors (11 Mar 2021) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (23 Mar 2021) by Stefania Gilardoni

AR by Cheng Fan on behalf of the Authors (24 Mar 2021) Manuscript

Short summary

Emission control policy in China has resulted in the decrease of nitrogen dioxide concentrations, which however leveled off and stabilized in recent years, as shown from satellite data. The effects of the further emission reduction during the COVID-19 lockdown in 2020 resulted in an initial improvement of air quality, which, however, was offset by chemical and meteorological effects. The study shows the regional dependence over east China, and results have a wider application than China only.

Variability of NO2 concentrations over China and effect on air quality derived from satellite and ground-based observations

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Variability of NO₂ concentrations over China and effect on air quality derived from satellite and ground-based observations