Vertical distribution of black carbon and its mixing state in the urban boundary layer in summer

Liu, Hang; Pan, Xiaole; Lei, Shandong; Zhang, Yuting; Du, Aodong; Yao, Weijie; Tang, Guiqian; Wang, Tao; Xin, Jinyuan; Li, Jie; Sun, Yele; Cao, Junji; Wang, Zifa

doi:https://doi.org/10.5194/acp-23-7225-2023

Articles | Volume 23, issue 12

https://doi.org/10.5194/acp-23-7225-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-23-7225-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 12

Research article

|

30 Jun 2023

Research article |

| 30 Jun 2023

Vertical distribution of black carbon and its mixing state in the urban boundary layer in summer

Hang Liu, Xiaole Pan, Shandong Lei, Yuting Zhang, Aodong Du, Weijie Yao, Guiqian Tang, Tao Wang, Jinyuan Xin, Jie Li, Yele Sun, Junji Cao, and Zifa Wang

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Final revised paper (published on 30 Jun 2023)
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Preprint (discussion started on 16 Jan 2023)
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Interactive discussion

Status: closed

RC1:
'Comment on acp-2022-736', Anonymous Referee #2, 22 Feb 2023

General Comments:
This manuscript analyzed the vertical distribution of concentration, mixing state, Dp/Dc, and optical properties of black carbon based on a meteorology tower (0-240 m) using AE33, SP2 and PAX. Four types of vertical profiles were found, and uniform type and gradual decrease type dominate. The differences between the ground and the residual layer were also compared, and the results would improve our understanding of the vertical distribution of BC and its mixing state. However, there are some issues that need major revision. In particular, there are many demonstrations without supporting data.

Major comments:
(1) English expression needs further improvement, which is not bad but needs to be re-checked carefully. Some sentences are not clear enough.
(2) A detail introduction of the vertical measurements of BC and its mixing state is missing. although the authors note that there are limited measurements, their results should be included for intact.
(3) Some conclusions are not supportive enought. for instance, the authors mentioned that the boundary layer in summer is relatively high. Then, how much does 0-240 m take up in the boundary layer? In addition, The variation in the boundary layer leads to such vertical profile type changes in Fig.3, but without showing the variations of boundary layer data. It is necessary to include boundary layer height throughout the day to support the discussion.
(4) "In fact, the several gradual decrease cases observed during the daytime generally occurred on cloudy days when the radiation was relatively weak." I donot find such data in Fig.3. Supporting data should be provided.

Specific comments:
1. Line 37: The expression of “the area” is not good. “the surrounding atmosphere” may be better.
2. Line 42: Change “study” to “studies”.
3. Line 50: “Shiraiwa et al. (2010) found that BC’s absorption ability after coating could reach two times greater than BC without coating.” The relationship between BC’s absorption ability and coating depends on many factors, the description here is not appropriate since the atmospheric conditions or particle properties are missing.
4. Line 59: What properties of BC has been measured? Concentration? Please describe clearly.
5. Line 88: Please describe clearly again. The sentence should be “The concentration of pollutant gases (…), the concentration and mixing state of BC, and optical properties (…) of aerosol were measured…”.
6. Section 2.2: Eabs is calculated at a wavelength of 550 nm, but the Dp used in the calculation of Eabs is calculated at a wavelength of 1064 nm. Does this lead to higher uncertainty in the calculation of Eabs? Please describe it with more details.
7. It is mentioned that the core-shell assumption will lead to overestimation of light absorption. Is the light absorption shown in the result section corrected?
8. Line 139: Reword to “…, which is consistent with…”.
9. Lines 148-150: As mentioned above, June 25 is an ozone pollution day with a maximum hourly mixing ratio of 124 ppb. From figure 1, the ozone mixing ratio is about 40 ppb on July 5. Is this the ozone pollution day?
10. Lines 174-175: From figure S12, the concentration of O3 increase with increasing height in the vertical profile at 18:00 on July 2, which is not consistent with the description here.
11. Line 178: Including a reference here would be helpful.
12. Lines 203-206: Please check carefully. The figure does not match with the text here. Figure S9 is not the vertical distribution on July 9. Moreover, the vertical distribution at 11:00 on July 9 is not sudden increase type in concentration of BC like the vertical profile at 11:00 on July 11. And, how do you figure out that the sudden increase in this case is due to solid fuel burning? Is there any other evidence here?
13. Lines 208-209: Reword to “…the vertical profiles of BC, including its concentration and mixing state,…”.
14. Lines 250-251: The figure does not match with the text again. From figure 4, the vertical profile of Dp/Dc at 23:00 slightly increase with height above 160 m. So the following explanation might be incorrect?
15. Line 262: Reword to “…than that in the residual layer.”
16. Line 263: It is better to change “more coatings” to “thicker coating”.
17. Lines 268-269: Note the preciseness of the data here. The MMD described here is inconsistent with that shown in the figure S7.
18. Lines 275-276 and 279: It should be “at 23:00 on June 27,…”.
19. Line 304: Reword to “…at the top of the boundary layer during the daytime…”.
20. Line 343: Dp/Dc represents the relative thickness of the coating of BC-containing particle. But, Dp/Dc is the diameter ratio of BC-containing particle to BC core, which is not shell to core.
21. The conclusion section is really tedious, mostly repeating the results. I suggest the authors focus on new findings.

Citation: https://doi.org/10.5194/acp-2022-736-RC1
- AC1: 'Reply on RC1', Hang Liu, 22 Mar 2023
  
  Please see the attachment.
  
  Citation: https://doi.org/10.5194/acp-2022-736-AC1
RC2:
'Comment on acp-2022-736', Anonymous Referee #3, 13 Mar 2023

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-736/acp-2022-736-RC2-supplement.pdf

Citation: https://doi.org/10.5194/acp-2022-736-RC2
- AC2: 'Reply on RC2', Hang Liu, 22 Mar 2023
  
  Please see the attachment.
  
  Citation: https://doi.org/10.5194/acp-2022-736-AC2

Peer review completion

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

AR by Hang Liu on behalf of the Authors (22 Mar 2023) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (12 May 2023) by Ottmar Möhler

AR by Hang Liu on behalf of the Authors (15 May 2023) Author's response Manuscript

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Short summary

We provide the average vertical profiles of black carbon (BC) concentration, size distribution and coating thickness at different times of the day in an urban area based on 112 vertical profiles. In addition, it is found that BC in the residual layer generally has a thicker coating, higher absorption enhancement and hygroscopicity than on the surface. Such aged BC could enter into the boundary layer and influence the BC properties in the early morning.