the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Retrieval of refractive index and water content for the coating materials of aged black carbon aerosol based on optical properties: a theoretical analysis
Abstract. Water content in the coatings of aged black carbon (BC) aerosol can be reflected through complex refractive index. In this study, the retrieval of refractive index and water content for the non-absorbing coatings of BC aerosol during the hygroscopic growth (RH=0–95 %) based on scattering and absorption properties is theoretically investigated. Optical properties of morphologically realistic fractal BC aerosols are simulated using the Multiple Sphere T-matrix method (MSTM), the optical equivalent refractive index of coating material is retrieved based on the Mie theory, and the water content in coatings is further retrieved using effective medium theory. Results show that the scattering property has the best performance in retrieving refractive index and water content. The retrieval errors of the refractive index of heavily-aged BC aerosols are less than 10 % at high RHs, while partially-coated and thinly-coated BC have larger errors. The retrieved water contents are similar to those of refractive index and the errors range from 2 % to 63 % for heavily-coated BC. This study provides a helpful optical method to obtain the water content of BC coatings.
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RC1: 'Comment on egusphere-2024-1000', I. Pérez, 02 May 2024
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This study is a theoretical analysis about the influence of water content of coatings on complex refractive index of aged black carbon. Three models are used, which are closed-cell model, partially coated model and coated-aggregate model. Varied simulations were made since different values of the most noticeable parameters involved were selected. For instance, the influence of relative humidity at different wavelengths, or particle radius was investigated. Consequently, the paper may be accepted for publication in Atmospheric Chemistry and Physics after the introduction of some minor changes.
The main inconvenience that authors should correct is the lack of citations in the results section. Some references should be introduced to indicate that these results are not isolated and can be compared with those from previous analyses. This comparison is useful to discuss the results of this research.
Moreover, a link with real situations, for instance, real cases with high concentration of black carbon and high relative humidity where this theory could be applied, should be encouraged. Similar examples should reveal that presented calculations respond to real conditions.
Minor remarks.
Figure-1 caption should be revised and corresponding labels should be introduced.
Dots after “Figure” in figure captions should be suppressed (from Figure 2 to Figure 9).
Some dots after “Figure” and figure number in text should be suppressed. For instance, L. 188, L. 208, L. 220, L. 239.
L. 214. Introduce one space between “(b)” and “and”.
References should follow the journal style.
Citation: https://doi.org/10.5194/egusphere-2024-1000-RC1 -
CC1: 'Partly coated soot is partly collapsed', J. C. Corbin, 04 Jun 2024
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This study aims to compute the optical properties of morphologically realistic soot--water mixtures. The authors have done a nice job of summarizing the results of MSTM calculations. The modelled particles represent 3 different morphologies: pure soot, partly coated, and fully encapsulated. (These are termed CCM, PCM, and CAM). I would like to suggest that the authors modify their PCM to represent partial compaction.
Multiple studies have observed that partial compaction occurs for partially coated soot. These studies have recently been reviewed in Corbin, Modini, and Gysel (https://doi.org/10.1080/02786826.2022.2137385) and in Sipkens and Corbin (https://doi.org/10.1016/j.carbon.2024.119197). The former study describes the physics of this restructuring and the latter study quantifies the relationship of coating to compaction. I recommend that the authors modify their PCM model to reflect the fact that almost all laboratory and field studies have observed that partly coated soot is partly collapsed.
Citation: https://doi.org/10.5194/egusphere-2024-1000-CC1
Data sets
Optical equivalent CRI of coated BC at different RH Jia Liu, Cancan Zhu, Donghui Zhou, and Jinbao Han https://doi.org/10.13140/RG.2.2.21765.36321
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