Measurement report: Fast photochemical production of peroxyacetyl nitrate (PAN) over the rural North China Plain during haze events in autumn

Qiu, Yulu; Ma, Zhiqiang; Li, Ke; Huang, Mengyu; Sheng, Jiujiang; Tian, Ping; Zhu, Jia; Pu, Weiwei; Tang, Yingxiao; Han, Tingting; Zhou, Huaigang; Liao, Hong

doi:https://doi.org/10.5194/acp-21-17995-2021

Articles | Volume 21, issue 23

https://doi.org/10.5194/acp-21-17995-2021

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

https://doi.org/10.5194/acp-21-17995-2021

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

Articles | Volume 21, issue 23

Measurement report

|

09 Dec 2021

Measurement report |

| 09 Dec 2021

Measurement report: Fast photochemical production of peroxyacetyl nitrate (PAN) over the rural North China Plain during haze events in autumn

Yulu Qiu, Zhiqiang Ma, Ke Li, Mengyu Huang, Jiujiang Sheng, Ping Tian, Jia Zhu, Weiwei Pu, Yingxiao Tang, Tingting Han, Huaigang Zhou, and Hong Liao

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Final revised paper (published on 09 Dec 2021)
Supplement to the final revised paper
Preprint (discussion started on 23 Jun 2021)
Supplement to the preprint

Interactive discussion

Status: closed

RC1:
'Comment on acp-2021-359', Anonymous Referee #1, 14 Jul 2021
General Comments:

The authors provided an analysis for the sources of abrupt PAN enhancement at Shangdianzi (SDZ) station on Oct 20 and Oct 25, 2020. The influences from regional transport were evaluated using CO as an inert tracer; the contributions from various precursors are then calculated based on observations. The authors found CH3CHO oxidation by OH is the major pathway of PAN formation at the SDZ site. I recommend the paper for publication after consideration of the points below.

Specific Comments:

Improvements in the language are suggested.

As shown in the title, the scientific importance of this paper relies on the validity of the conclusion to represent rural North China Plain during the cold season haze events. However, it is unclear whether the analysis based on a single station during pollution events (3 days) has enough representation.

Lines 236-251: More details should be provided for the calculation in this section. The Phys is calculated with dCO/dt * PAN/CO in Eq. 2. However, I assume Eq. 2 should consider PAN and CO along the transport pathway, particularly, the source domain, instead of SDZ site itself.

Section 3.4: The authors indicated that the contribution from CH3CHO oxidation by OH is larger than that from other precursors. I am wondering whether the total contributions from precursors can explain the observed PAN enhancement, quantitatively?

Technical Comments:

Line 130-136: improvement in the language is suggested as continuous “In addition” and “Here” are used.

Line 146: It seems Zhu et al. 2018 is not southern coast region.

Line 163: which were 10.6 and 7.7 times those during clean days.

Line 213: the increases of PAN on pollution days impossibly caused by direct PAN transport.

Lines 214-215: rephrase this sentence: “Here, direct transport impact is restricted to PAN that has been formed in other regions, but exclusive of PAN precursors”.

Line 228: what is “urban city”?

Lines 240-241: rephrase this sentence: “It should be noted that the calculation of physical transport impact aims at PAN that has been formed outside of the SDZ site”.
Citation: https://doi.org/10.5194/acp-2021-359-RC1
- AC1: 'Reply on RC1', Z.Q. Ma, 08 Sep 2021
  
  We thank the reviewer’s very helpful suggestions which we believe greatly improve our manuscript. Please see our response in the supplement.
  
  Citation: https://doi.org/10.5194/acp-2021-359-AC1
RC2:
'Comment on acp-2021-359', Anonymous Referee #2, 16 Jul 2021
This manuscript investigated the occurrence of PAN, typical VOCs, PM_2.5, HONO and various trace gases during cold season haze events in the North China Plain, to elucidate the cause of rapid increase of PAN. The article was well written with pre-established methodology. The authors provide some useful information about the formation of wintertime PAN. Overall this manuscript should be accepted after the authors address the issues below.

Title: I don’t think it is a representative results for cold-season, exactly in autumn, based on the limited observation data.

Highlight the new findings of this study. The authors should demonstrate the creative results, especially to differentiate those in previous studies. I think, studies on the occurrence of PAN have been widely obtained. The authors should introduce more studies about them, and discuss the formation mechanisms of PAN, especially in autumn.

Analytical method appeared adequate; however some key procedural and QA/QC details on the observation of PAN, typical VOCs, HONO and various trace gases are missing. Please provide more detailsin the manuscript.

The authors mentioned that, “Formaldehyde (HCHO) photolysis dominates the daytime HOx production thus contributing to fast photochemistry of PAN”. Limited VOCs species were measured in this study. How about the contributions of other VOCs species? Other studies had found that acetaldehyde was regarded as the most important precursor of PAN during winter in Beijing, could you explain it?

For production rates of HOx and PA under different pollution level, do you compare them with OBM-MCM analysis?

The authors are suggested to discuss the impact of environmental factors (including temperature, wind speed and SLP, etc) on the pollution characteristics of PAN.
Citation: https://doi.org/10.5194/acp-2021-359-RC2
- AC2: 'Reply on RC2', Z.Q. Ma, 08 Sep 2021
  
  We are grateful for the reviewer’s invaluable comments. We have carefully addressed all the comments. Please see our response in the supplement.
  
  Citation: https://doi.org/10.5194/acp-2021-359-AC2
RC3:
'Comment on acp-2021-359', Anonymous Referee #3, 02 Aug 2021
General comments:

This paper explored enhancements in PAN over the North China Plain at the Shangdianzi (SDZ) site for two October days. After meteorological analysis, the authors determined that direct PAN transport was impossible given the timing of prevailing southerlies and used CO as a tracer to confirm. Local enhancements in photochemistry were determined to be the source of enhanced PAN. Authors used observations of various precursor species to calculate respective contributions and found that oxidation of acetaldehyde by the hydroxyl radical was the main pathway for PAN formation at the SDZ site.

I recommend this paper for publication given the following minor edits:

Specific comments:

The title suggests generalizability to all cold-season haze events, though 3 October days were examined. Additional observation/analysis is necessary in order to determine generalizability to all cold-season pollution events with PAN enhancements. Revision to the wording of the title is suggested.

The authors concluded that conditions were anomalously warm and wet for days of study, though title suggests "cold-season". As a reader, I question whether results are generalizable to "cold-season" days when anomalously warm and wet conditions are not present.

Figure 3b -- it is unclear as to what "clean days" refers to.

Improvements in grammar and language are suggested.

Technical comments:

Line 116 - listed chemical species naming is not consistent with respect to chemical formula and English name use.

Line 185 - lack of consistency in naming wind directions. "Southwesterly" should be used rather than "Northwestern". "Southwesterly" should be followed by "winds" to be complete (i.e. Southwesterly winds)

Line 186 - sentence reads “..the SDZ site was in the south of a strong” should read “...the SDZ was to the south of a strong..”

Line 187 - sentence reads “The southwesterly on 10/25 was caused by a weak high-pressure system with anticyclone in the southeast” should read “the southwesterly winds on 10/25 were caused by a weak high-pressure system with an anticyclone in the southeast.”

Line 195 - “meridian” should be “meridional”

Line 217 - Wind direction naming consistency -- “southern wind” should be changed to “northerly wind” if this is what is meant.

Lines 240-245 are not interpretable by the reader because the meaning of (Chem + Phys), (Chem), (Phys), were not clearly defined.

Line 335 - “while our results was based on” should be “while our results were based on”

Line 358, 395 - wind direction naming consistency needed.
Citation: https://doi.org/10.5194/acp-2021-359-RC3
- AC3: 'Reply on RC3', Z.Q. Ma, 08 Sep 2021
  
  We appreciate the positive feedback from the reviewer. All the concerns have been addressed in the supplement.
  
  Citation: https://doi.org/10.5194/acp-2021-359-AC3

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Z.Q. Ma on behalf of the Authors (08 Sep 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (19 Sep 2021) by Eleanor Browne

RR by Anonymous Referee #1 (23 Sep 2021)

ED: Reconsider after major revisions (02 Oct 2021) by Eleanor Browne

Dear Authors,
Thank you for your consideration of the referee comments. The revisions largely address the referee comments. Before accepting this manuscript for publication however, I think that a few additional points require consideration.

Main comment
Further elaboration on the modeling using PAN/CO ratios is required in the manuscript. The equations from Section S1 should be moved to the main text along with a brief explanation. Additionally, further information is required about how the PAN and CO concentrations are selected for the model. It seems to me that the PAN/CO ratio used in the calculation should be the ratio from the urban environment. Please provide a brief discussion on why you think the PAN/CO ratio selected is appropriate to represent the urban environment. A brief discussion on biases and limitations of this calculation are also warranted.

How consistent is the chemical production rate calculated using the PAN/CO method to that calculated using the PA radical production rates? This would require an estimation of the PA radical loss to obtain the PA radical concentration. It would also require NO2 concentrations, for which the measurement may be influenced by PAN. Nevertheless, I think a rough comparison would be instructive and would support the PAN/CO method.

Minor comments
1. Several references to the cold season still remain in the manuscript (e.g. lines 19. 75. 349, and others). Please edit to clarify that it is autumn.
2. There are several locations where I think the manuscript overstates aspects of the work. For instance, line 25 “proving is too strong a word and in line 30 “fully explain” is not appropriate given the type of model used. Similar comments apply to line 92 (“suggest” may be more appropriate than “explain”), line 101 (“perfect” should be deleted), line 245 (“exclude” should probably be replaced with something along the lines of “deemed to be unlikely”).
3. Line 139: I believe that model of NOx analyzer may detect some PAN as NO2. Given the focus of the manuscript, it may be useful to remind the reader of this.
4. Line 160: Although the concentrations are in table S2, it would be helpful for the reader if you provide representative ranges for the different locations you are discussing.
5. Line 184: The reduction in photolysis rates is not evident from the data provided in the figures or the tables. Please include this data either in the main text or in the SI.
6. Figure 3a (northwesterly winds line 201) seems inconsistent with Fig. 1b (northeasterly/southwesterly lines 101-102). Is this due to the averaging used or the height? Please clarify.
7. Line 213/Figure 4: The temperature on 10/20 appears to be lower than the temperature on the preceding days. Furthermore, from Fig. 4f there appears to be extremely little variability in the mean or median temperature between the clean days and either 10/20 or 10/25. It suggests that the result of a positive temperature anomaly is not statistically significant. Further discussion/clarification is warranted.
8. Lines 375-378: The comparison of photolysis rates is not particularly meaningful without further information about the different measurements. What times of year are the measurements? Are these all compared at the same time of day? Does the HCHO concentration or the photolysis rate drive the differences?

Technical
1. Line 46: These compounds are oxidation products of various NMHCs. Please correct the wording.
2. Line 49: OH is the primary oxidant during the day, not necessarily the primary radical. Please revise.
3. Line 123: Please make sure all relevant gases are listed. The use of “etc” suggests that perhaps they are not. For instance, is MGLY measured? The calculations in section 3.4 suggest that it was.
4. Line 124: Please provide the length of the inlet.
5. Line 127/Table S1: The time resolution of the PTR measurements is inconsistent. Please fix.
6. Line 199: Please define SLP at its first use.
7. Line 237: I believe this should be 12:00 pm (noon), not 12:00 am (midnight).
8. Line 286: Photolysis rates should be given as J and then subscript species name.
9. Line 310: The sentence implies that Figure 4e shows wind direction, but instead it shows wind velocity. Please make the text and figures consistent.
10. Line 330: I think “calculated” rather than “observed” is a better choice since HOx production is calculated and not measured.
11. Line 333: I think you mean to say that the production rate of OH from HO2+NO is higher than the HOx sink from HO2+HO2. The current wording though implies that HO2+HO2 also produces HOx. Please clarify. Similarly in Table S3, the “production rate” column labeling is misleading/confusing. Production rate of what? I think HO2+HO2 is a loss rate.
12. Please label reactions in the supplement differently from the main text so that the reader isn’t confused as to which R1 you refer.

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AR by Z.Q. Ma on behalf of the Authors (04 Nov 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (05 Nov 2021) by Eleanor Browne

AR by Z.Q. Ma on behalf of the Authors (12 Nov 2021) Author's response Manuscript

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Short summary

Photochemical pollution over the North China Plain (NCP) is attracting much concern. Our observations at a rural site in the NCP identified high peroxyacetyl nitrate (PAN) concentrations, even on cold days. Increased acetaldehyde concentration and hydroxyl radical production rates drive fast PAN formation. Moreover, our study emphasizes the importance of formaldehyde photolysis in PAN formation and calls for implementing strict volatile organic compound controls after summer over the NCP.