Preprints
https://doi.org/10.5194/egusphere-2024-1000
https://doi.org/10.5194/egusphere-2024-1000
15 Apr 2024
 | 15 Apr 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Retrieval of refractive index and water content for the coating materials of aged black carbon aerosol based on optical properties: a theoretical analysis

Jia Liu, Cancan Zhu, Donghui Zhou, and Jinbao Han

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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Jia Liu, Cancan Zhu, Donghui Zhou, and Jinbao Han

Status: open (extended)

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  • RC1: 'Comment on egusphere-2024-1000', I. Pérez, 02 May 2024 reply
Jia Liu, Cancan Zhu, Donghui Zhou, and Jinbao Han

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

Jia Liu, Cancan Zhu, Donghui Zhou, and Jinbao Han

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Short summary
The hydrophilic coatings of aged black carbon (BC) particles absorb moisture during the hygroscopic growth process, but it is difficult to characterize how much water is absorbed under different relative humidities (RHs). In this study, we propose a method to obtain the water content in the coatings based on the equivalent complex refractive index retrieved from optical properties, and this method is verified from theoretical inspect. This method performs well for thickly coated BC at high RHs.