Identifying the Fraction of Core–Shell Black Carbon Particles in a Complex Mixture to Constrain the Absorption Enhancement by Coatings
Kang Hu, Dantong Liu, Ping Tian, Yangzhou Wu, Siyuan Li, Delong Zhao, Ruijie Li, Jiujiang Sheng, Mengyu Huang, Deping Ding, Quan Liu, Xiaotong Jiang, Qian Li, Jing Tao
Abstract
The coatings mixing with the refractory black carbon (rBC) may enhance its light absorption (Eabs). Uncertainty largely arises from to what extent the coatings can envelope the rBC, in addition to the particle-resolved diversities for rBC size, coatings, and their combinations. Here, by using in situ characterization of particle morphology for all ambient BC, we propose a single metric to well discriminate the BC populations with and without Eabs, which is the dynamic shape factor (χ) to describe the effect of particle nonsphericity in enhancing the drag force in an electrical field compared to a volume-equivalent sphere (higher χ means more nonspherical). BC with χ ≤ 1.75 can be considered well capsulated by coatings showing Eabs, while χ > 1.75 is not. Given the initial nonsphericity of BC, increasing coatings causes BC to approach more sphericity and more likely encapsulates the rBC, thus exerting Eabs. By applying this scenario, we are able to identify the fraction (F) of the BC mass with Eabs present (likely core–shell) from a complex mixture (linearly correlated with a logarithmic coating/rBC volume ratio (VR), parametrized as F = 0.27 × log(VR) + 0.36), by which the predicted Eabs in bulk can be improved by 36% compared to a core–shell only model, well capturing the transition of the BC mixing state when increasing coatings.