Mixing characteristics of refractory black carbon aerosols at an urban site in Beijing

Liu, Hang; Pan, Xiaole; Liu, Dantong; Liu, Xiaoyong; Chen, Xueshun; Tian, Yu; Sun, Yele; Fu, Pingqing; Wang, Zifa

doi:https://doi.org/10.5194/acp-20-5771-2020

Articles | Volume 20, issue 9

https://doi.org/10.5194/acp-20-5771-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-5771-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 9

Research article

|

14 May 2020

Research article |

| 14 May 2020

Mixing characteristics of refractory black carbon aerosols at an urban site in Beijing

Hang Liu, Xiaole Pan, Dantong Liu, Xiaoyong Liu, Xueshun Chen, Yu Tian, Yele Sun, Pingqing Fu, and Zifa Wang

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Interactive discussion

Status: closed

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

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RC1: 'Review', Anonymous Referee #2, 17 Jun 2019
- AC1: 'Reply to Anonymous Referee #2', Hang LIU, 06 Dec 2019
RC2: 'Review', Anonymous Referee #3, 29 Oct 2019
- AC2: 'Reply to Anonymous Referee #3', Hang LIU, 06 Dec 2019

Peer-review completion

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

AR by Hang Liu on behalf of the Authors (06 Dec 2019)

ED: Referee Nomination & Report Request started (09 Jan 2020) by Thomas Karl

RR by Anonymous Referee #2 (29 Jan 2020)

Suggestions for revision or reasons for rejection

The manuscript has clearly improved in terms of clarity, specially the methodology section through more detailed explanations of the techniques and the experiments performed. The English language has also been improved.
The study combines different approaches to apportion/characterize rBC particles and its mixing state in a measurement site near Beijing during summer, which I consider to be suitable for publication in ACP. However, in my opinion, there are several points that need improvement before final publication, especially in terms of presenting the results in a precise, logical sequence and integrating the different types of analysis. The results subsections appear to be decoupled from each other, which make it difficult to read. This concern could be improved, at first, by reformulating the last paragraph of the introduction (L75-L82) and briefly presenting the organization of the paper. This paragraph could “… provide the readers with the expectation of what they will find out by reading your paper” (Schultz, David M, 1965 – Eloquent Science). Moreover, I think the following aspects need further clarification:
L78: Please specify what are the typical cases and the microphysical properties.

L212-214: You mention a clear diurnal pattern – is it in terms of concentration or MMD? I think the whole discussion (L212-215) could be better illustrated by a diurnal cycle plot. In my opinion, the type of plot does not correspond with the discussion.

L216-217: The same as the comment before. This sentence could be better illustrated by showing the size distributions of before vs. after rain, or similar. The statement cannot be easily observed in Fig 5 or in Fig.3.

L228-230: Is the larger MMD in southerly air masses only due to the different combustion source or is it also related to the aging time in the atmosphere?

L246-252: In my opinion Figure 7 is quite complex and with some excess of information that is not used in the discussion or necessary to prove the main point. I suggest ‘cleaning’ this figure. Moreover, I could not fully understand the colormap (dN/dlogDp) vs. (Dp/Dc, in linear scale). Could you please clarify how did you calculate this? The same applies for the upper panels. I think the “dN/dlogDp” should be a “normalized frequency”, please check. Also consider to give indexes (a), (b) and (c) for each of the panels in Fig. 7.
Figs 3, 5 and 7: please put the x-axis in the same time format and same time range since they all correspond to the same measurement. You should also consider to combine them into one single plot, with the information of the time window of the rain events, the tandem experiment and other events that were used in the analyses. Note that the PM2.5 is presented in all of them.
L252-256: I found these sentences quite confusing.

L255: The authors say Dc/Dp = 1.8 in L255 but Dc/Dp = 1.4 in L248 for the polluted case.

L258-272: You consider the aging process responsible for the increase in Dp/Dc. Could that be related to the advection of aged particles (thickly coated) when the BL is developed? Did you consider discriminating the periods when the site is influenced by northerly or southerly winds?

Minor comments:

Figure 1. The paper is about influence of Beijing outflow on the measurement site. I suggest pointing the city on the map in (a) or outline the city borders in (b). This will be very helpful for the reader.

Figure 4. You present the number size distribution in Fig. 4 but make no reference to that in the text.

L22: The microphysical properties of rBC were also studied.

L94: intense vs. intensive.

L96: To be consistent, use “rBC mass”.

L 106: Put the equation in a separate line and number it.

L 115: Liu et al. (2015)
When presenting your results, always round numbers to appropriate digits. (e.g. L186, L194, L201) (https://en.wikipedia.org/wiki/Significant_figures).
L149: Please rephrase: “where many heavy industries are located”. Moreover, I assume it is not only industries, correct?
L209-210: The term “urban sites” is used 2 times.

L225 and Fig. 5 – As I am not familiar with wind rose plots, I was puzzled when you made the reference to the angle values. Where does your angle scale starts? I would expect the angle of 45 degrees to be heading in a NE direction.

L239: investigation period.

L378: On “A simulation showed that the Eabsaveraged” there is a space missing.

L303: Maybe “mixture” instead of “structure”.

L304: “approaches” instead of “was equal to”.

Avoid starting sentences with symbols or acronyms (e.g. L24, L260, L282, L297, L346).

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ED: Publish subject to minor revisions (review by editor) (07 Feb 2020) by Thomas Karl

AR by Hang Liu on behalf of the Authors (21 Mar 2020)

ED: Publish subject to minor revisions (review by editor) (27 Mar 2020) by Thomas Karl

AR by Hang Liu on behalf of the Authors (06 Apr 2020) Author's response Manuscript

ED: Publish as is (09 Apr 2020) by Thomas Karl

AR by Hang Liu on behalf of the Authors (13 Apr 2020) Author's response Manuscript

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Short summary

The bare black carbon (BC) was in a fractal structure. With coating thickness increasing, BC changed from a fractal structure to a core–shell structure. In the ambient atmosphere, plenty of BC particles were not in a perfect core–shell structure. This study brought attention to the combined effects of morphology and coating thickness on the absorption enhancement of BC-containing particles, which is helpful for determining the climatic effects of BC.