Preprints
https://doi.org/10.5194/egusphere-2024-1155
https://doi.org/10.5194/egusphere-2024-1155
14 May 2024
 | 14 May 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Technical note: Numerical quantification of the mixing states of partially-coated black carbon based on the single-particle soot photometer: Implication for global radiative forcing

Jie Luo, Miao Hu, Jibing Qiu, Kaitao Li, Hao He, Yuping Sun, and Xiulin Geng

Abstract. In this work, we have performed a series of numerical investigations on the mixing states of partially-coated black carbon (BC) based on the single-particle soot photometer (SP2). First, we calculated the scattering signal returned from partially-coated BC based on the SP2 measurement, and then the mixing states were determined using Mie theory, where the difference between the determined and "true" mixing states can represent the uncertainties of the SP2 measurement. We found that the SP2 measurement can provide good estimates for small, heavily coated BCs and shows better performance for fully coated BCs. However, the microphysical properties of BCs have a significant impact on the accuracy of the SP2 measurement; sometimes deviations of about -22 % to 28 % were observed for the determined particle-to-core size ratio (Dp/Dc). When considering a size distribution, the error in the effective radius is generally within about -17 % to 8.8 %. We also investigated the effects of Mie-based models using the SP2 determined and volume-mean Dp/Dc on the radiative effects of partially-coated BC. We found that both Mie models based on the volume mean and SP2 determined mixing states overestimate the absorption enhancement (Eabs) and direct radiative forcing (DRF) of BC. The Mie model based on the SP2 measurement does not necessarily provide worse estimates of radiative properties, although some errors occur in the determination of the mixing states, since the fraction of the coated core (F) in the particle scale is an important factor affecting Eabs and DRF. Sometimes the inaccurate measurements of the mixing states by SP2 would offset the influence of F. Moreover, our results based on the Mie model considering F can significantly improve the estimates for the absorption and DRF of partially-coated BC, although the morphology also has some influence. Therefore, we suggest adding a parameter F to model the radiative effect of BC in climate modeling even when a Mie-based model is used.

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Jie Luo, Miao Hu, Jibing Qiu, Kaitao Li, Hao He, Yuping Sun, and Xiulin Geng

Status: open (until 25 Jun 2024)

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Jie Luo, Miao Hu, Jibing Qiu, Kaitao Li, Hao He, Yuping Sun, and Xiulin Geng
Jie Luo, Miao Hu, Jibing Qiu, Kaitao Li, Hao He, Yuping Sun, and Xiulin Geng

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Short summary
In this work, we first calculate the scattering signal returned from partially-coated black carbon based on the SP2 measurement, and then the mixing states were retrieved using Mie theory, and the difference between the retrieved and "true" mixing states can be the uncertainties of the SP2 -Represent measurement. In addition, the effects on the direct radiative forcing are also evaluated.