Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: roles of regional transport and heterogeneous reactions of SO<sub>2</sub>

Du, Huiyun; Li, Jie; Chen, Xueshun; Wang, Zifa; Sun, Yele; Fu, Pingqing; Li, Jianjun; Gao, Jian; Wei, Ying

doi:https://doi.org/10.5194/acp-19-9351-2019

Articles | Volume 19, issue 14

https://doi.org/10.5194/acp-19-9351-2019

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

Special issue:

In-depth study of air pollution sources and processes within...

https://doi.org/10.5194/acp-19-9351-2019

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

Articles | Volume 19, issue 14

Research article

|

22 Jul 2019

Research article |

| 22 Jul 2019

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: roles of regional transport and heterogeneous reactions of SO₂

Huiyun Du, Jie Li, Xueshun Chen, Zifa Wang, Yele Sun, Pingqing Fu, Jianjun Li, Jian Gao, and Ying Wei

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Preprint (discussion started on 27 Nov 2018)
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Status: closed

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

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RC1: 'comments on acp-2018-1189', Anonymous Referee #1, 17 Dec 2018
RC2: 'Review', Anonymous Referee #2, 16 Jan 2019
- AC1: 'Authors' reply and the marked-up manuscript', Jie Li, 17 Mar 2019

Peer-review completion

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

AR by Jie Li on behalf of the Authors (13 Apr 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Apr 2019) by James Allan

RR by Anonymous Referee #1 (19 Apr 2019)

RR by Anonymous Referee #2 (25 Apr 2019)

Suggestions for revision or reasons for rejection

The authors have addressed most of my previous comments. However, several parts of the new text are hard to understand and should be clarified. In addition, there are several instances where language should be improved; I listed a few examples below.

Scientific comments

l. 35: Remove ‘these changes would affect regional radiation and climate’ as these consequences are not discussed in the manuscript.

l. 95-97: ‘The heterogeneous reaction parameters are rarely related to the key parameters such as mixing state and aerosol water contents in previous studies.’ - This sentence is not clear. Do you mean that there is not much data available that describe the parameters for heterogeneous reactions as a function of aerosol composition and water content? Please add a reference that shows these dependencies and lack of data.
I suggest rewording ‘For many heterogeneous reactions, comprehensive data sets for the reaction parameters as a function of aerosol composition and water content are not available.’

l. 132: Please specify the aqueous processes that are included. Is it only the oxidation reactions of S(IV) by O3, H2O2, methyl hydroperoxide and peroxyacetic acid? Or does it also include additional reactions, e.g. the redox chemistry of metal ions - as your response to my previous review implies?

l. 134: ‘are related with aerosol water’. I suggest adding some more details of the calculation of SO2 as it is not intuitive that an uptake coefficient depends on the aerosol water content. For example:
‘Assuming that the upper limit of γ𝑆𝑂2 does not exceed the uptake coefficient on dust surfaces, the upper limit of γ𝑆𝑂2 is 10-4 for AWC > 300 g m-3 and its lower limit is 10-6 if AWC < 10 g m-3. More details can be found in Li et al., (2018).’

l. 217: ‘heterogeneous chemistry to sulfate’- do you mean ‘heterogeneous formation of sulfate’?

l. 329: How is ‘aging degree’ quantified? There might be several measures that can be used to describe how aged a particle is, such as the coating thickness of BC or the oxidation degree of OA. However, to my knowledge, there is no universal model parameter that describes the ‘aging degree’.

l. 368: ‘mechanisms of PA…formation’. ‘Formation’ implies that these aerosols are chemically formed; however, PA (primary aerosols) are directly emitted and do not undergo any formation processes.

l. 393: I had already asked in my previous review about the classification of PA and OM. It should be clarified that PA only includes primary inorganic aerosol (perhaps name it PIA) as you clarified now that OM includes both primary and secondary organic aerosol.

l. 407 and l. 409: Specify: …contributing up to 30% and 19% to total PM2.5 levels?

l. 613: This sentence is hard to understand now. Do you mean the following?
- ‘RBC in Beijing during the episodes was higher than that of OTHER urban regions (Collier et al., 2018)’?
- At high pollution levels, RBC was close to that in remote regions (Wang et al., 2017a)

l. 617-621: This text seems contradictory:
‘In episodes with high humidity (Ep1), the average contributions of gas and aqueous chemistry, heterogeneous chemistry, and primary sulfate were comparable.’

‘…heterogeneous chemistry played a relatively crucial role under high pollution levels during Ep1.’

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Technical comments

l. 28: ‘…was the major form of SO42− regional transport’ is unclear. Do you mean ‘was the major source of SO42-‘?

l. 44/45: ‘has been experiencing’ or ‘has experienced’

l. 114: Detailed analysis of…

l. 356: ‘non-organic’ should be ‘inorganic’

l. 443: ‘convinced’ seems to be a wrong word here; ‘supported’ might fit better.

l. 505: ‘…had undergone a greater degree of aging’ sounds awkward. It should be, for example, ‘had undergone more ageing’ or ‘had reached a higher degree of ageing’

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ED: Publish subject to minor revisions (review by editor) (26 Apr 2019) by James Allan

AR by Jie Li on behalf of the Authors (06 May 2019) Author's response Manuscript

ED: Publish as is (08 May 2019) by James Allan

AR by Jie Li on behalf of the Authors (16 May 2019) Manuscript

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Short summary

Regional transport and heterogeneous reactions play crucial roles in haze formation. Using a chemical transport model, we found that chemical transformation of SO₂ along the transport pathway from source regions to Beijing was the major source of sulfate. Heterogeneous chemistry had a stronger effect under high humidity and high pollution levels. Aerosols underwent aging during transport which altered the aerosol size and the degree of aging.

Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: roles of regional transport and heterogeneous reactions of SO2

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Modeling of aerosol property evolution during winter haze episodes over a megacity cluster in northern China: roles of regional transport and heterogeneous reactions of SO₂