NH<sub>3</sub>-promoted hydrolysis of NO<sub>2</sub> induces explosive growth in HONO

Xu, Wanyun; Kuang, Ye; Zhao, Chunsheng; Tao, Jiangchuan; Zhao, Gang; Bian, Yuxuan; Yang, Wen; Yu, Yingli; Shen, Chuanyang; Liang, Linlin; Zhang, Gen; Lin, Weili; Xu, Xiaobin

doi:https://doi.org/10.5194/acp-19-10557-2019

Articles | Volume 19, issue 16

https://doi.org/10.5194/acp-19-10557-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Multiphase chemistry of secondary aerosol formation under...

https://doi.org/10.5194/acp-19-10557-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 16

Research article

|

21 Aug 2019

Research article |

| 21 Aug 2019

NH₃-promoted hydrolysis of NO₂ induces explosive growth in HONO

Wanyun Xu, Ye Kuang, Chunsheng Zhao, Jiangchuan Tao, Gang Zhao, Yuxuan Bian, Wen Yang, Yingli Yu, Chuanyang Shen, Linlin Liang, Gen Zhang, Weili Lin, and Xiaobin Xu

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

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RC1: 'RC coments', Anonymous Referee #1, 04 Jan 2019
- AC1: 'Reply to reviewer #1', Ye Kuang, 08 Mar 2019
RC2: 'Anonymous Review', Anonymous Referee #2, 21 Jan 2019
- AC2: 'Response to reviewer #2', Ye Kuang, 08 Mar 2019

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

AR by Ye Kuang on behalf of the Authors (08 Mar 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (14 Mar 2019) by Aijun Ding

RR by Anonymous Referee #3 (28 May 2019)

Suggestions for revision or reasons for rejection

I have mixed feeling about this paper. The authors propose a very interesting point that NH3 may promote the heterogeneous production of HONO and thus positively affect the oxidation processes and secondary aerosol formation. If it was true, it provides important inputs for the understandings of the heterogeneous chemistry of NOx and the unknown sources of HONO. However, there are also several major issues regarding the measurement techniques, budget analysis and interpretation of the results. I would like to recommend that this manuscript can be considered for publication after the following concerns being properly addressed.

A major concern is about the measurement of HONO by the IGAC. To my experience, such wet denuder system usually tends to overestimate HONO compared to the other instruments such as LOPAP and DOAS. This may explain why the measured HONO/NO2 ratios in this study are so large, almost one order of magnitude higher than the other studies over the world. Furthermore, this HONO/NO2 ratio should be even underestimated in this study considering the potential overestimation of NO2 (I presume that the Thermo NO2 analyzer should use catalytic converter that may subject significant interference at non-urban sites). A rough check can be made by comparing the measured HONO+NO3-+NO2- against NO2. If catalytic converter was used, the measured “NO2” should include NO2 and some NOz species including HONO, NO3- and NO2-, etc. For most cases, the explosive growth of HONO was dominated by only one data point (e.g. 4th and 14th November). Such results are in general possibly affected by the potential measurement interference for this data point. So the authors are encouraged to thoroughly evaluate the performance of this IGAC system for the HONO measurements. Additional inter-comparison experiments should be helpful for validating the IGAC measurements and exclude the potential interferences during the foggy and high RH conditions.

Another concern is on the HONO budget analysis. The Equation 1 was only valid under the assumption of steady state where production and loss of HONO were in balance. Would such an assumption stand in this study, especially for the morning period and foggy or high RH conditions? The OH concentration is a key factor with large uncertainty in such a budget analysis. The diurnal variation of OH levels used for the calculation should be provided in the supplement. It is not clear why the authors choose different uptake coefficients for the uptake of NO2 on ground (1*10^-6 and 2*10^-5) and aerosol surfaces (10^-4 to 10^-3). The uptake coefficients are highly uncertain and still under debate. How did the selections of OH and uptake coefficients affect the analysis results in this study? Furthermore, large discrepancy exits between the calculated and observed d[HONO]/dt from Figure 5. What’s the possible reason for such discrepancy?

For Equation 8, I suggest to use the partitioning of HNO3 to the aerosol phase to instead the k[NO2][OH]. Using k[NO2][OH] may underestimate the nitrate formation if the ambient HNO3 was abundant. I presume the measurement data of HNO3 should be available from the IGAC system.

Section 4.2: could the authors comment on how NH3 involve in the heterogeneous reactions of NO2? Does particulate ammonium work in the same manner? Is there any other indication that NH3 promotes the heterogeneous HONO production other than the moderate correlation between HONO/NO2 and NH3?

Lines 88-89: delete “for the first time” as wet denuder systems have been widely used in field studies.

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ED: Reconsider after major revisions (30 May 2019) by Aijun Ding

AR by Ye Kuang on behalf of the Authors (11 Jun 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Jun 2019) by Aijun Ding

RR by Anonymous Referee #3 (22 Jul 2019)

ED: Publish as is (27 Jul 2019) by Aijun Ding

AR by Ye Kuang on behalf of the Authors (31 Jul 2019) Author's response Manuscript

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Short summary

The study of HONO, the primary source of OH radicals, is crucial for atmospheric photochemistry and heterogeneous chemistry. Heterogeneous NO₂ conversion was shown to be one of the missing sources of HONO on the North China Plain, but the reaction path is still under debate. In this work, evidence was found that NH₃ was the key factor that promoted the hydrolysis of NO₂, leading to the explosive growth of HONO and nitrate, suggesting that NH₃ emission control measures are urgently needed.

NH3-promoted hydrolysis of NO2 induces explosive growth in HONO

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NH₃-promoted hydrolysis of NO₂ induces explosive growth in HONO