Fast particulate nitrate formation via N<sub>2</sub>O<sub>5</sub> uptake aloft in winter in Beijing

Wang, Haichao; Lu, Keding; Chen, Xiaorui; Zhu, Qindan; Wu, Zhijun; Wu, Yusheng; Sun, Kang

doi:https://doi.org/10.5194/acp-18-10483-2018

Articles | Volume 18, issue 14

https://doi.org/10.5194/acp-18-10483-2018

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

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https://doi.org/10.5194/acp-18-10483-2018

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

Articles | Volume 18, issue 14

Research article

|

23 Jul 2018

Research article |

| 23 Jul 2018

Fast particulate nitrate formation via N₂O₅ uptake aloft in winter in Beijing

Haichao Wang, Keding Lu, Xiaorui Chen, Qindan Zhu, Zhijun Wu, Yusheng Wu, and Kang Sun

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Final revised paper (published on 23 Jul 2018)
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Preprint (discussion started on 11 Jan 2018)
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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Referee cpmment', Anonymous Referee #1, 19 Mar 2018
RC2: 'Review of Large particulate nitrate formation from N2O5 uptake in a chemically reactive layer aloft during wintertime in Beijing', Anonymous Referee #2, 20 Mar 2018
- AC2: 'Response to Referee #2', Keding Lu, 22 Apr 2018
AC1: 'Response to Referees #1', Keding Lu, 22 Apr 2018

Peer-review completion

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

AR by Keding Lu on behalf of the Authors (22 Apr 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (04 May 2018) by Mei Zheng

RR by Anonymous Referee #3 (03 Jun 2018)

Suggestions for revision or reasons for rejection

COMMMEMTS on manuscript entitled “Large particulate nitrate formation from N2O5 uptake in a chemically reactive layer aloft during wintertime in Beijing” by H. Wang et al., 2017

General comments:
Kinetics and mechanisms of nitrate formation are of great concern in our society, and the manuscript has reported considerable Ox (O3+NO2) loss in the nocturnal residual layer in winter Beijing, immediately indicates potential nitrate formation in that nocturnal residual layer in winter Beijing, since the dominate sink of Ox is known to be nitrate formation. The authors also construct a model and run several sensitivity tests to illustrate that the N2O5 uptake is mainly responsible for the Ox loss and thus the inorganic nitrate formation stands out. Therefore, I would recommend publication of this manuscript on ACP on condition that specific weakness（see below）is resolved.

Specific comments:
1. The main premise for your analysis on the air mass evolution (or inorganic nitrate formation) overnight is that you have measured the same air mass in the evening measurement and the next morning measurement. However, dilution, exchange and mixing of the air mass cannot be ruled out considering the non-zero wind speed. How would the uncertainties originated from physical changes of the air mass affect your analysis and those many conclusions?
2. If the story of Ox loss and inorganic nitrate formation in the nocturnal residual layer in winter Beijing in one of your measurements is credible regardless of question #1, I did not see why you could safely extrapolate the story of the specific case study to (1). the winter nights since no gradient of NO, NO2 and O3 has been spotted in your measurements. (2) general situation of Beijing (3) the 50 ug m-3 contribution due to (1) and (2), and also that the structure of nocturnal boundary layer is not characterized anywhere in your study.
3. Constraint or comparison of your model to your measurements of Ox would help
4. Need great improvement in English writing. Here only the comments on the first page (line1-line31) of the manuscript are listed:
Line 1: consider “fast/rapid formation” or “big formation rate”
Line 2: define “chemical reactive layer”
Change “during wintertime in Beijing” to “in winter Beijing”
Line 13: is not “dominant”
Line 16: measurement of what?
Line 18: change to “due to N2O5 concentration of near zero controlling by high NO emission and NO concentration”
Line19: No will not “limiting the production of N2O5”
Larger or large, higher or high (if being specific on altitude like > 150 m, just delete “high”)
Line 20: Large or larger (Large is not a proper adj. for formation or missing)
Line 21: define “production potential”
Line 22: higher or high
Line 23: delete “significantly”
Line 24-27: a conclusion drawn from nowhere, hard to follow
Line 28：higher or high
Line 30: define “reactive air masses”
Line 28-31: “haze formation”, “formation and development of the reactive air masses” is not the topic of this study. Also, be specific on how are you going to improve the “chemical-transport model” based on the contribution of your study?

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RR by Anonymous Referee #4 (05 Jun 2018)

Suggestions for revision or reasons for rejection

General comments:

As noted by the other reviewers of this manuscript, the paper presents new results on the formation of nitrate aerosol by N2O5 uptake at modest altitudes above surface level during winter in Beijing. The result is important since ozone titration by NOx at surface level makes the production rate at the surface zero. The paper quantifies the production rate in an altitude range up to 250 m above the surface and is thus a valuable contribution to the literature.

The authors quantify uncertainties in their analysis due to NO3 reactivity and ClNO2 production, both of which are unmeasured. They do not quantify the uncertainty due to partitioning between gas phase HNO3 and particulate nitrate. This aspect should be addressed, even if it is simply to state by way of assumption that all nitrate formed from N2O5 uptake goes to the particle phase rather than the gas phase. If the authors have other information to indicate that partitioning (other literature) they should state this explicitly.

Otherwise the manuscript should be published subject to the following minor comments and grammatical corrections.

Specific comments:

Line 26: remove the word “easily”

Line 27: The result for gamma(N2O5) is specific to the very large aerosol surface area present in Beijing during these events. The sentence in the abstract should note this so as not to imply that a gamma value of 2x10-3 is generally the point at which other regions would become insensitive to this parameter.

Line 28: Suggest replacing “could be” with “is”. At the author’s discretion.

Line 43: replace “severely limited” with “very low in concentration”

Line 162 and equation 5: The idea behind the definition of s(t) is fairly clear, but the form of equation 5 is not. Further explanation of the form of the equation is required.

Figure 2: The scale for O3 in the upper panel goes to 100 ppbv, while the O3 itself only goes to 25 ppbv. The scale should show the actual variability in O3.

Line 235: The choice of kNO3 is arbitrary and is intended to simply represent a high value. The word arbitrary should appear in the sentence, i.e., “… kNO3 was set to an arbitrary and relatively high value of …”

Line 268: Do the authors mean to refer to December 19 rather than December 18?

Line 277: Is NO greatly diminished, or zero? Nonzero O3 at night implies zero NO if the mixing ratio of O3 is sustained for any length of time.

Line 303: Omit the word “about”

Line 306: “rapid” in place of “quick”

Line 314: What relationship between Ox and pNO3- has been used to calculate the Ox equivalence in Figure 6? Have the authors assumed a 1:1 relationship, or have they used the Ox equivalent in pNO3, which is larger than 1? See: Brown et al., Nocturnal odd-oxygen budget and its implications for ozone loss in the lower troposphere. Geophys. Res. Lett., 2006. 33: p. L08801.

Line 332: Can the authors compare the 28 micrograms m-3 figure to the day over day change in nitrate mass during haze events in Beijing? In other words, what is the daily growth in nitrate mass during either this event or during typical events, and how much is explained by this 28 microgram m-3 per night rate?

Line 334: To what feature are the authors referring in stating a morning peak of 60 micrograms m-3 on Dec 20? This feature is not apparent in Figure 1.

Line 346: Correct English grammar. Use a period and new sentence rather than a comma. The second part of the sentence should read: “Low N2O5 uptake coefficients correspond to several types of aerosols, such as …”

Line 352: Logic of sentence is incorrect. The ClNO2 yield is not the variable that maximizes the conversion capacity of N2O5, as the sentence implies. Rephrase as: “The conversion capacity of N2O5 uptake to pNO3 is maximized for a given, fixed value of the ClNO2 yield”

Line 363: It is not clear what is intended by the phrase “valid NOx loss.” The authors should clarify or search for other wording.

Line 364: “the N2O5 uptake coefficient” rather than “N2O5 uptake”

Line 369: remove the word “was”

Line 373: “become insensitive to gamma(N2O5).” Then start a new sentence “This region is defined as …”

Line 387: Sentence needs improved English grammar. The meaning of “during the heating period” is not clear. Does this refer simply to colder weather during the winter season?

Line 394: This result of 2.5 ppbv refers to a model, not a measured value. This should be made clear.

Line 397: “As the error of pNO3 formation simulation was subject to” should be replace by “Since the modeled pNO3 formation is sensitive to”

Line 399: The reference is to Figure 8, not Figure 7

Line 415: replace “evidenced” with “found evidence for”

Line 718, figure caption 7: “via N2O5 uptake” rather than “on N2O5 uptake”, “NO2 and O3 were set to”, “Sa was set”, “reaction time was set “

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ED: Publish subject to minor revisions (review by editor) (09 Jun 2018) by Mei Zheng

Dear authors,
There are four reports so far with two previous reports and two current reports. After reviewing your revised manuscript, the current two referees suggest to publish after minor revisions. Please respond to their comments carefully.

One of the previous referee has a major concern and the referee feels that it is not directly responded in your previous revised manuscript . Please include your response to this following comment and revise the manuscript accordingly.
"The topic of the heterogeneous process of NOx is of interest to the community, and the vertical measurements of chemical composition in winter haze are particularly valuable. My main concern, however, on the present work is that the model was poorly constrained by observations and had to reply on too many assumptions. The vertical measurements only included O3, NO, and NO2 which enabled calculation of NO3 production, but several key parameters, such as N2O5, VOCs and aerosol surface area density, for loss of NO3, N2O5 production and subsequent loss to nitrate were not measured, making it very difficult, if not impossible, to evaluate nighttime reactions of NOx and for nitrate formation. In addition, the analysis was only based on one profile measured in the early evening, and too many assumptions in the model calculations were not well justified. All these make it very difficult to judge the validity of the conclusions drawn from the analysis. The authors are advised to carefully consider and reduce these uncertainties which could lead to large bias and possible errors."

Another concern by the referee is that the referee tends to agree with these many conclusions in this manuscript based on general judgement, but not the evidences the author has provided. Therefore, please put more effort in validation of the main conclusion, which is about Ox loss and inorganic nitrate formation in one night observation, and should avoid to extraplate one observation to all Beijing nights.

Please address the above comments and revise your manuscript based on these comments. If you have any questions, please let me know.

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AR by Keding Lu on behalf of the Authors (27 Jun 2018) Author's response Manuscript

ED: Publish as is (09 Jul 2018) by Mei Zheng

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Short summary

The vertical measurement of NO_x and O₃ was carried out on a movable carriage on a tower during a winter heavy-haze episode in urban Beijing, China. We found that pNO₃^- formation via N₂O₅ uptake was significant at high altitudes (e.g., > 150 m), which was supported by the lower total oxidant (NO₂ + O₃) level at high altitudes than at ground level. This study highlights the fact that pNO₃^- formation via N₂O₅ uptake may be an important source of pNO₃^- in the urban airshed during wintertime.

Fast particulate nitrate formation via N2O5 uptake aloft in winter in Beijing

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Fast particulate nitrate formation via N₂O₅ uptake aloft in winter in Beijing