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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-600
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 29 Jun 2018

Research article | 29 Jun 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Effects of brown coatings on the absorption enhancement of black carbon: a numerical investigation

Jie Luo, Yongming Zhang, Feng Wang, and Qixing Zhang Jie Luo et al.
  • State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui 230026, China

Abstract. Using the numerically exact multiple sphere T-matrix (MSTM) method, we explored the effects of brown coatings on absorption enhancement (Eabs) and the lensing effects (Eabs_lensing) of black carbon (BC) at different wavelengths (λ). Eabs increases with the absorption of coatings, while an opposite trend is observed for Eabs_lensing. A much wider range of Eabs is observed for BC with brown coatings compared to that with non-absorbing coatings. Eabs can reach approximately 5.4 for λ=0.35μm given a typical size distribution. In addition, previous studies have focused on the lensing effects of coatings but neglected the blocking effects of absorbing coatings. Eabs_lensing can be below 0.5 at ultraviolet spectral region for BC with brown coatings, which indicates that the absorption of internal BC is diluted by approximately 0.5 times due to the blocking effects of outer coatings, and we named the blocking effect of absorbing coatings "sunglasses effect". Hence, it is imperative to take the blocking effects of outer coatings into consideration for estimation of total aerosol absorption. Cabs of thickly-coated BC is underestimated by core-shell sphere model for all wavelengths while the underestimation becomes negligible as kBrC turns very large. Eabs and Eabs_lensing are insensitive to the size distribution for thinly-coated BC, and the uncertainties caused by the size distribution have differences of less than 2.6% and 6%, respectively. However, the effects of size distribution on Eabs and Eabs_lensing are rather obvious for thickly-coated BC. In addition, the uncertainties in Eabs and Eabs_lensing caused by Df are less than 9%. Eabs seems to be essentially wavelength-independent for thickly-coated BC with non-absorbing coatings but rather wavelength-dependent for thickly-coated BC with brown coatings.

Jie Luo et al.
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Jie Luo et al.
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Short summary
The absorption enhancement and lensing effect of black carbon with brown coatings are investigated. The enhancement factor induced by lensing effect of thickly coated BC can be less than 1 due to the blocking effect of brown coatings at UV wavelengths, and we named this phenomenon “sunglasses effect” for the first time. The applicability of core-shell sphere model was investigated. The effects of the size distribution, fractal dimension and wavelength dependency are also explored.
The absorption enhancement and lensing effect of black carbon with brown coatings are...
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