Sulfate formation during heavy winter haze events and the potential contribution from heterogeneous SO<sub>2</sub> + NO<sub>2</sub> reactions in the Yangtze River Delta region, China

Huang, Ling; An, Jingyu; Koo, Bonyoung; Yarwood, Greg; Yan, Rusha; Wang, Yangjun; Huang, Cheng; Li, Li

doi:https://doi.org/10.5194/acp-19-14311-2019

Articles | Volume 19, issue 22

https://doi.org/10.5194/acp-19-14311-2019

© 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-19-14311-2019

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

Articles | Volume 19, issue 22

Research article

|

27 Nov 2019

Research article |

| 27 Nov 2019

Sulfate formation during heavy winter haze events and the potential contribution from heterogeneous SO₂ + NO₂ reactions in the Yangtze River Delta region, China

Ling Huang, Jingyu An, Bonyoung Koo, Greg Yarwood, Rusha Yan, Yangjun Wang, Cheng Huang, and Li Li

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Final revised paper (published on 27 Nov 2019)
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Preprint (discussion started on 29 Apr 2019)
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Status: closed

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

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RC1: 'Review of Huang et al. (2019)', Anonymous Referee #1, 25 May 2019
- RC2: 'Technical correction to peer-review report', Anonymous Referee #1, 25 May 2019
- AC2: 'Reply to Reviewer #1', Ling Huang, 24 Aug 2019
RC3: 'Comment on acp-2019-202', Anonymous Referee #2, 27 May 2019
- AC1: 'Reply to Reviewer #2', Ling Huang, 24 Aug 2019
- AC3: 'Reply to Reviewer #2', Ling Huang, 24 Aug 2019

Peer-review completion

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

AR by Ling Huang on behalf of the Authors (29 Aug 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Sep 2019) by Hang Su

RR by Anonymous Referee #2 (12 Sep 2019)

RR by Anonymous Referee #1 (16 Sep 2019)

Suggestions for revision or reasons for rejection

Review of revised version of Huang et al. (2019)

The authors has gone a long way improving their manuscript, by conducting additional model runs, calculations, and adding new discussions. Indeed, the paper in its current form provides much more results and insights than in its original form. With notable contributions to the modeling community by adding pH dependence of SO2+NO2 reaction beyond the work of Zheng et al. (2015) and making comparisons to modeling results in other places and studies, the paper is a useful addition to the literature. Nevertheless, I still feel that the paper needs further improvements in another round of revision, by refining the method of parameterization, and ‘calibrate’ the conclusions derived from the results so that they align better with the presented results.

Specifically, the use of “γ” from Wang et al. (2016) to back calculate model parameters is problematic and needs to be rethought about. Wang et al. (2016) derived an empirical “γ” from ambient observations, assuming that all the sulfate was from the SO2+NO2 source. This is a big assumption that has obvious issues. As demonstrated by the model results, SO2+NO2 is by no means the sole contributor to enhanced sulfate transitioning from clean to polluted periods. Thus, in my first review, I recommended deriving their own “γ” using observations and modeling results in Shanghai. The assumption behind this approach is that the enhanced sulfate not explained by the model, i.e., the difference between observed and modeled sulfate in standard model without the new SO2+NO2 source, is solely contributed by the new source. A similar approach was taken by Cheng et al. (2016). The rebuttal of this idea because of ‘lacking all necessary observed data’ is not convincing at all to me, because modeled and observed data should be equivalent in such context. It almost appears to suggest that the authors deems a modeled value in Shanghai not as credible as an observed value in Beijing. If that were true, what would be the purpose of modeling Shanghai? Furthermore, the first-order approach used by Wang et al. (2016) served their goal well to roughly estimate the magnitude and significance of a newly discovered source. However, such an empirical “γ” value by itself is by no means more robust or trustworthy than the authors’ modeled + observed results in Shanghai. A more rigorous approach to estimating “γ” using ‘local’ relevant data, observed or modeled, is definitely warranted.

Regarding the conclusion, given the uncertainties found by the authors, i.e., the relatively low level of transition metals compared to Shao et al. (2019), the biased low pH compared to observed (Figure 8), I would suggest the authors rewrite their conclusion and abstract, and even the title, to emphasize the uncertainty of the role of SO2+NO2 reaction (perhaps all sources, for example, the modeled OH might be uncertain as well), rather than emphasizing the importance of SO2+NO2, which is not supported by its magnitude or accuracy.

Minor comments:

The spatial resolution of the MEIC inventory is clearly not 12 km in Figure S1. Please check and correct.

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ED: Reconsider after major revisions (18 Sep 2019) by Hang Su

AR by Ling Huang on behalf of the Authors (02 Oct 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Oct 2019) by Hang Su

RR by Anonymous Referee #1 (16 Oct 2019)

ED: Publish as is (25 Oct 2019) by Hang Su

AR by Ling Huang on behalf of the Authors (27 Oct 2019) Manuscript

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Short summary

Severe haze events characterized by extremely high concentrations of particulate matter occurred frequently in the Yangtze River Delta (YRD) region, China. Rapid sulfate production during these severe haze episodes was observed via atmospheric measurements but air quality models tend to underestimated sulfate. Our study suggests that the SO₂+NO₂ heterogeneous reactions could be potentially important for sulfate formation in the YRD region and ammonia emissions need to be carefully estimated.

Sulfate formation during heavy winter haze events and the potential contribution from heterogeneous SO2 + NO2 reactions in the Yangtze River Delta region, China

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Sulfate formation during heavy winter haze events and the potential contribution from heterogeneous SO₂ + NO₂ reactions in the Yangtze River Delta region, China