The absorption Ångstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization

Zhang, Xiaolin; Mao, Mao; Yin, Yan; Tang, Shihao

doi:https://doi.org/10.5194/acp-20-9701-2020

Articles | Volume 20, issue 16

https://doi.org/10.5194/acp-20-9701-2020

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

https://doi.org/10.5194/acp-20-9701-2020

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

Articles | Volume 20, issue 16

Research article

|

19 Aug 2020

Research article |

| 19 Aug 2020

The absorption Ångstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization

Xiaolin Zhang, Mao Mao, Yan Yin, and Shihao Tang

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Final revised paper (published on 19 Aug 2020)
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Preprint (discussion started on 26 Mar 2020)

Interactive discussion

Status: closed

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

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RC1: 'Review of The absorption Angstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization by Zhang et al.', Anonymous Referee #1, 20 Apr 2020
- AC2: 'Author comment on Anonymous Referee #1', Xiaolin Zhang, 02 Jun 2020
RC2: 'Review of “The absorption Angstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization” by X Zhang et al.', Anonymous Referee #2, 01 May 2020
- AC3: 'Author comment on Anonymous Referee #2', Xiaolin Zhang, 02 Jun 2020
AC1: 'Author comments on "The absorption Angstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization"', Xiaolin Zhang, 02 Jun 2020

Peer-review completion

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

AR by Xiaolin Zhang on behalf of the Authors (02 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Jun 2020) by Manvendra Krishna Dubey

RR by Anonymous Referee #2 (28 Jun 2020)

Suggestions for revision or reasons for rejection

I think the paper presents highly valuable results and the findings are definitely worth publication. The author did a reasonable job addressing the reviewers' comments and the paper is more readable now. I still think the paper would benefit from some editorial work to improve readability and correct grammar issues; in particular, in the newly added sentences.
Just a few examples (but many more are present):
1. In the abstract: "more large BC particle..." do the authors mean "BC particles with larger coating" or "a larger number of BC coated particles" or something else? From the paper it seems quite plausible that they mean "BC particles with larger coating", but as it is the sentence can be confusing for the reader as they start reading through the paper. A very similar issue with the sentence "if there are plenty of small coated BC particles...", and "...for smaller coated volume fraction of BC"; does "smaller" refer to the fraction of BC or for BC particles that are smaller in size? Again the interpretation becomes evident after reading the rest of the paper but more clarity since the beginning would help readability.
2. "...the absorbing organics, named brown carbon (BrC), absorbs radiation" maybe should be "the absorbing organics... absorb"?
3. "Therefore, in ambient measurements, large AAE is considered to be that aerosols originate from dust or biofuel/biomass burning, while small AAE near 1.0 is understood to be that aerosols are BC-rich particles due to the burning of fossil fuel", maybe "Therefore, in ambient measurements, large AAE is considered to indicate that aerosols originate from dust or biofuel/biomass burning, while small AAE near 1.0 is understood to indicate that aerosols are BC-rich particles due to the burning of fossil fuel"
4. "It is observed that BC particles can externally attached to, partially coated in, or fully encapsulated in coatings [China et al., 2013, 2015]. This study considers BC aggregate core with a spherical coating, following the coated BC models built by Zhang et al. [2018], and the sketch maps of three typical coated BC structures considered (i.e., externally attached, partially coated and fully coated) are portrayed in Figure 1." maybe reword as "It is observed that BC particles can be externally attached to, partially coated in, or fully encapsulated by coatings [China et al., 2013, 2015]. This study considers a BC aggregate core with a spherical coating, following the coated BC models built by Zhang et al. [2018]. The sketch maps of three typical coated BC structures considered here (i.e., externally attached, partially coated, and fully coated) are portrayed in Figure 1."
5. "The AAE of coated BC aggregates is also slightly sensitive to BC Df, and the sensitivity shows weaker as Dp/Dc or F become larger." maybe could be rephrased as: "The AAE of coated BC aggregates is also slightly sensitive to the Df of BC, and the sensitivity becomes weaker as Dp/Dc or F increase."
6. "This is probably due to that the absorption of BC coated by BrC with core-shell Mie model show slower increase with decreased wavelength than that of coated BC with realistic particle geometry." maybe could be rephrased as: "This is probably because the absorption of BC coated by BrC calculated from the core-shell Mie model shows a slower increase with decreased wavelength than that calculated using realistic particle geometry."
7. The sentence "coating. It should be noticed that no one has ever definitively separated BrC from organic carbon, and to a certain extent, the concept of f here may be treated as that the cases of BrC with imaginary parts of refractive indices less than those of Kirchstetter et al. [2004] are considered due to a range of BrC refractive indices being provided [Schuster et al., 2016]." is very confusing, please consider rewording it and maybe breaking it down into two sentences.
8. Line 27, page 8: "small coated BC" again does this indicate small BC particles that are coated or BC particles that have a thin (small) coating?
9. "The correlation coefficient for parameterizing with three variables (i.e., f , / p c DD, and F ) is mildly smaller than that with one variable (i.e., each of f , / p c DD, and F ), and". I am confused by this sentence, I would guess that the more parameters one uses the higher the correlation coefficient should be, so "is mildly smaller" seems weird... but maybe I am misunderstanding the sentence here. I would consider revising this sentence to make it clearer.
10. Line 10 page 11: "more large coated BC" see previous comments on these kinds of expressions.

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ED: Publish subject to minor revisions (review by editor) (28 Jun 2020) by Manvendra Krishna Dubey

AR by Xiaolin Zhang on behalf of the Authors (30 Jun 2020) Author's response Manuscript

ED: Publish as is (17 Jul 2020) by Manvendra Krishna Dubey

AR by Xiaolin Zhang on behalf of the Authors (18 Jul 2020)

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Short summary

The understanding of the absorption Ångstrom exponent (AAE) of aged black carbon (BC) particles affected by their microphysics is numerically evaluated. With key sensitive microphysical parameters, a simple parameterization of the AAE of coated BC with a size distribution is proposed. It is found that BC coated by thin brown carbon with more large particles shows an AAE smaller than pure BC particles. Our findings improve the understanding and application of the AAE of BC with brown coatings.