Ozone seasonal evolution and photochemical production regime in the polluted troposphere in eastern China derived from high-resolution Fourier transform spectrometry (FTS) observations

Sun, Youwen; Liu, Cheng; Palm, Mathias; Vigouroux, Corinne; Notholt, Justus; Hu, Qihou; Jones, Nicholas; Wang, Wei; Su, Wenjing; Zhang, Wenqiang; Shan, Changong; Tian, Yuan; Xu, Xingwei; De Mazière, Martine; Zhou, Minqiang; Liu, Jianguo

doi:https://doi.org/10.5194/acp-18-14569-2018

Articles | Volume 18, issue 19

https://doi.org/10.5194/acp-18-14569-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Quadrennial Ozone Symposium 2016 – Status and trends...

https://doi.org/10.5194/acp-18-14569-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 19

Research article

|

11 Oct 2018

Research article |

| 11 Oct 2018

Ozone seasonal evolution and photochemical production regime in the polluted troposphere in eastern China derived from high-resolution Fourier transform spectrometry (FTS) observations

Youwen Sun, Cheng Liu, Mathias Palm, Corinne Vigouroux, Justus Notholt, Qihou Hu, Nicholas Jones, Wei Wang, Wenjing Su, Wenqiang Zhang, Changong Shan, Yuan Tian, Xingwei Xu, Martine De Mazière, Minqiang Zhou, and Jianguo Liu

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Final revised paper (published on 11 Oct 2018)
Supplement to the final revised paper
Preprint (discussion started on 18 Dec 2017)

Interactive discussion

Status: closed

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

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- Supplement

SC1: 'HCHO/NO2', Jason Schroeder, 20 Dec 2017
- AC1: 'Response to short comments (SCs) from the scientific community', Youwen Sun, 22 May 2018
RC1: 'referee's comments', Anonymous Referee #1, 05 Feb 2018
- AC2: 'Response to referee #1', Youwen Sun, 28 Jun 2018
RC2: 'Manuscript review', Anonymous Referee #2, 05 Feb 2018
- AC3: 'Response to referee #2', Youwen Sun, 28 Jun 2018
RC3: 'Interesting, but very long', Anonymous Referee #3, 08 Apr 2018
- AC4: 'Response to referee #3', Youwen Sun, 28 Jun 2018

Peer-review completion

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

AR by Youwen Sun on behalf of the Authors (28 Jun 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Jun 2018) by Stefan Reis

RR by Anonymous Referee #4 (27 Jul 2018)

Suggestions for revision or reasons for rejection

Ozone seasonal evolutionand photochemical production regimein polluted troposphere in eastern China derived from high resolution FTS observations
By Y. Sun and collegues

Following the referee’s remarks, the revised version has been strongly reorganized as compared to the initial version. As the authors state, (1) they have updated all retrievals with new Sa deduced from standard deviation of a dedicated WACCM run from 1980 to 2020, (2) they have organized the paper’s structure, with focus on new results, and retaining only the most pertinent figures, (3) they omitted comparisons with the correlative data, i.e., OMI, GEOS-Chem and WRF-Chem data, (4) the reoriented the papers focus on photochemical ozone regime. In my view, this responded to the major referee remarks, and makes the paper rather different from the initial one. I think, the paper shows now interesting results on data at a specific site and an interesting discussion of the ozone formation regime that can be deduced from the data. However, there is a major difficulty, because from reading the paper I think that the O3 product is not specific for PBL O3, which would be needed for the current analysis. So I would think the paper is in principle worthwhile for publication in ACP, but only if this major issue is resolved or correctly addressed. Also figures should be better explained and a general rereading by a native speaker would be needed.

In Section 3, it is not clear to me, what exactly are the altitude ranges of the partial columns that are the basis for the paper, and whether they are for the case of ozone pertinent, that is focusing on lower tropospheric ozone.
For instance, it is stated in section 3 : “In this study, we have chosen the same upper limit for the tropospheric columns for all gases, which is about 3 km lower than the mean value of the tropopause (~15.1 km).” If I understand right, this means that 0 – 12 km partial columns are considered. But looking at figures S2 and S3, such columns would be sensitive to O3 values up to 15 km. Following figure S3, wouldn’t it be wiser to analyse a 0 – 8km partial column being most sensitive between 0 and 6-8 km ? This would allow being more sensitive to lower tropospheric ozone.
Anyway, it seems that O3 partial columns used here are heavily influenced, if not dominated by free tropospheric (FT) ozone located between, say, 2 – 8 km height. Note that it would be useful to dispose of boundary layer height values allowing to state where the FT begins. This important, if not dominant, FT part for ozone needs to be clearly stated in the paper, while in the current version, it is suggested that the analysed product is representative for PBL O3. If authors think that their product has not only some fractional, but dominant information from the PBL, then please explain and prove it much better. Note that this applies for ozone, for NO2 and HCHO, the PBL sensitivity is stronger because both compounds are concentrated there.
If this suspected FT sensitivity is real, then the analysis needs to be taken into account in the following analysis. While PBL ozone can be strongly regionally controlled, FT ozone is prone to intercontinental or even hemispheric transport, including stratosphere – troposphere exchange. This needs to be addressed, and may be , the analysis completed or redirected. This point is really important to be addressed before publication.
Minor remarks :
Abstract :
Introduction:
“Briefly, VOCs first react with the hydroxyl radical (OH) to form a peroxy radical (HO2+ RO2) which increases the rate of catalytic cycling of NO to NO2. O3 is then produced by subsequent reactions between HO2or RO2 and NO that lead to radical propagation (via subsequent reformation of OH). «
Please reformulate :
“Briefly, VOCs first react with the hydroxyl radical (OH) to form a peroxy radical (HO2+ RO2) which increases the rate of catalytic cycling of NO to NO2. O3 is then produced by photolysis of NO2. Subsequent reactions between HO2or RO2 and NO lead to radical propagation (via subsequent reformation of OH). «

Section 4.1 :
“While it failed to determine the secular trend of tropospheric O3 column probably because the time series is much shorter than those in Gardiner et al. (2008),”
This sentence suggests that the O3 trend needs to be positive, but for later years, this is not necessarily the case, especially in the free troposphere.
Section 4.2
“The direction of east origin air masses shifts from the southeast to northeast of Jiangsu Province, and that of local origin air masses shifts from the south to the northwest of Anhui province.”
Please reformulate :
“The direction of air masses originating in the eastern sector shifts from the southeast to northeast of Jiangsu Province, and that of local air masses shifts from the south to the northwest of Anhui province.”

“In contrast, trajectories of local origin air masses in SON/DJF are 20.2% larger than the MAM/JJA ones, indicating a more significant contribution of the air pollution inside Anhui province in SON/DJF.”
You mean, they are more frequent (instead of larger)?
5.1 Meteorological dependency
“The city downtown locates in eastern of the observation site and the majority of the Chinese population lives in the eastern part of China, easterly winds (direction less than 180˚) could generally transport more pollutants to the observe area than westerly winds (direction larger than 180˚), resulting in a higher O3 level.”
This again supposes, that the O3 product is mostly sensitive top PBL O3, which is clearly not proven. This also long range transport, not necessarily only from easterly regions, because trajectories can change directions, should contribute to enhanced O3 columns.

Section 5.2 :
“Pronounced tropospheric CO and NO2 variations were observed but the seasonal cycles are not evident probably because of air pollution which is not constant over season or season dependent.”
This is not clear. For NO2 a winter maximum is found. One reason is that time series are not complete enough especially in the later years.
“Since the sensitivity of PO3to VOCs and NOx is different under different limitation regimes, the relative weaker overall correlations to HCHO (Figure 6 (b)) and NO2 (Figure 6 (c)) indicates that the O3 pollution in Hefei can neither be fully attributed to NOx pollution nor VOCs pollution.”
If O3columns are representative for PBL, then weaker correlation of O3 with NO2 and HCHO are also explained by different lifetimes, hours to 1 day in summer for NO2 and HCHO, several days to weeks for O3. So older O3 enhanced air masses easily loose trace of NO2 or HCHO. Please add this explanation. If they are dominated by FT O3, then a correlation can not be expected anyway. This seems to be the case.

Figure 1:
In figure 1, how is the trend calculated ? how are the points named ‘resampled bootstrap” obtained. Please explain in the text.
Figure 3 :
Monthly average wind speed of 0 does not make sense, as already stated by another referee. It is understood that the average of absolute wind speed is meant. If you cannot calculate it, please withdraw this figure. Also the figure on wind direction on wind direction is not easy to interprete. May be a solution is to calculate frequency distributions.

Figure 4:
If minute average FTS measurements are used, then there should be much more points? Or do you use time averages ?
Figure 5 and Figure 6 : again, what is the measurement period one point corresponds to ?

Supplement:
“FigureS2. Averaging kernels(ppmv/ppmv)of O3, CO, and HCHO (color fine lines), and their area scaled by a factor of 0.2 (black bold line).They are deduced from the spectra recorded in Hefei on March 15, 2016 with a measured ILS.”
Please clarify several points in the figures legend. Each curve is representative for 1 km ? What does the area curve exactly indicate ? what does “ILS” stand for ?

“FigureS3. Partial column averaging kernels(PAVK)(ppmv/ppmv) for O3, CO, and HCHO retrievals. For all gases, large PAVKs in certain altitude range”
Are the PAVK’s obtained by summing up the km wise AVK’s ?

Referee Report: PDF

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RR by Anonymous Referee #3 (21 Aug 2018)

Suggestions for revision or reasons for rejection

The authors have revised the manuscript quite extensively and have addressed many of the concerns raised by the reviewers. The manuscript now has a much clearer message and storyline. The questionable comparisons to other observations and model simulations have been removed from the previous version.

I think that this is now publishable in the ACP special edition, after a few mostly minor revisions.

Generally, the English should be improved throughout the manuscript, especially in the later sections. I assume that much of this will be done in the copy-editing phase.

line 22: I would delete "different". I think "and modelling" also needs to be deleted, because modelling is not really used anymore in the revised version.

lines 30,31 (and 232,233; 452,453): I find this awkward. Why not state the June value 1.5e18? Given the variations and uncertainties 47.6% should probably be 50%. It would also be useful to give these column densities in Dobson Units (DU): 1.5e18 1/cm2 = 56 DU, 1.05e18/cm2 = 39 DU

lines 32 to 35: This sentence does not make sense to me. MAM/JJA is mainly influence by transport whereas MAM/JJA is mostly determined by photochemical production? Please rethink and reword.

line 40: % of what? Probably "of days" or "of cases". Change as appropriate.

line 42: delete "most of the". This has not been shown.

line 222: I would replace "failed to determine the" by something like "the analysis did not indicate a significant"

line 229: delete "it shows that"

lines 237 to 240: Not really true. Izana also shows an early summer maximum in May, at a latitude not too different from Heifei. Somewhere, you should also state that the tropospheric columns at these stations are of the order of 0.7e18/cm2 to 1.1e18/cm2, around 30% lower than at Heifei.

lines 249 to 251: I find this sentence confusing and I suggest to omit it.

line 262, and throughout section 4.2.: In most cases "air pollution" should be replaced by "air masses". The trajectory does not tell you anything about air pollution and its photo-chemical effects. It just tells you where the air masses (might) come from. Everything else is assumptions and plausibility.

line 276: Replace "dominate the contribution" by "contributes". Without a quantitative analysis, you do not know what dominates.

line 277: Replace "masses" by "trajectories".

line 282: replace "smaller" by "less frequent"

line 300: delete "which can be"

lines 308 to 318, Figs. 3 and 4: I am a bit worried/ puzzled about the wind data. Wind direction seems to be all over the place, and wind speeds seems to vary greatly between minutes and hours. Where do these short wind gusts come from? How representative is the local scale weather-station wind for the tropospheric FTIR columns? It might be much better to use larger scale winds, e.g. from the GDAS data? I think the wind data in Figs. 3 and 4 need careful checking, and it may be necessary to change or drop these panels and their discussion.

lines 339, 340: Something wrong with that sentence. Please fix.

lines 368 to 385: I don't think any of this information is needed here, and I find it more confusing than helpful. I suggest to drop this text.

lines 414 to 423: So this study finds a VOC - NOx transition regime at HCHO/NOx ratios between 1.3 and 2.8, whereas previous (in situ based) studies found it at HCHO/NOx ratios between 1 and 2. I think this is pretty good agreement and could be emphasized. You point out that your study is not in-situ, and this could explain some differences. Could you please also add a statement about possible chemical differences?

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RR by Anonymous Referee #5 (11 Sep 2018)

ED: Publish subject to minor revisions (review by editor) (12 Sep 2018) by Stefan Reis

AR by Youwen Sun on behalf of the Authors (24 Sep 2018) Author's response Manuscript

ED: Publish as is (24 Sep 2018) by Stefan Reis

AR by Youwen Sun on behalf of the Authors (25 Sep 2018) Author's response Manuscript

Post-review adjustments

AA: Author's adjustment | EA: Editor approval

AA by Youwen Sun on behalf of the Authors (09 Oct 2018) Author's adjustment Manuscript

EA: Adjustments approved (09 Oct 2018) by Stefan Reis

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Short summary

The seasonal evolution of O₃ and its photochemical production regime in a polluted region of eastern China between 2014 and 2017 was investigated using FTS observations. We observed a broad summer O₃ maximum in Hefei, China, and the ozone production is mainly NO_x limited in spring and summer and is mainly VOC or mixed VOC–NO_x limited in autumn and winter.