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Measuring morphology and density of internally mixed black carbon with SP2 and VTDMA: new insight to absorption enhancement of black carbon in the atmosphere

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Cheng,  Y. F.
Multiphase Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Su,  H.
Multiphase Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Wang,  Z. B.
Multiphase Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Citation

Zhang, Y. X., Zhang, Q., Cheng, Y. F., Su, H., Kecorius, S., Wang, Z. B., et al. (2015). Measuring morphology and density of internally mixed black carbon with SP2 and VTDMA: new insight to absorption enhancement of black carbon in the atmosphere. Atmospheric Measurement Techniques Discussions, 8, 12025-12050. doi:10.5194/amtd-8-12025-2015.


Cite as: https://hdl.handle.net/11858/00-001M-0000-002A-3D4E-A
Abstract
he morphology and density of black carbon (BC) cores in internally mixed BC (In-BC) particles affects their mixing state and absorption enhancement. In this work, we developed a new method to measure the morphology and effective density of BC cores of ambient In-BC particles using a single particle soot photometer (SP2) and a volatility tandem differential mobility analyzer (VTDMA), during the CAREBeijing-2013 campaign from 8 to 27 July 2013 at Xianghe Observatory. The new measurement system can select size-resolved ambient In-BC particles and measure the mobility size and mass of In-BC cores. The morphology and effective density of ambient In-BC cores are then calculated. For In-BC cores in the atmosphere, changes in the dynamic shape factor (χ) and effective density (ρeff) can be characterized as a function of aging process (Dp ⁄ Dc) measured by SP2 and VTDMA. During an intensive field study, the ambient In-BC cores had an average χ of ∼ 1.2 and an average density of ∼ 1.2 g cm−3, indicating that ambient In-BC cores have a near-spherical shape with an internal void of ∼ 30 %. With the measured morphology and density, the average shell ⁄ core ratio and absorption enhancement (Eab) from ambient black carbon were estimated to be 2.1–2.7 and 1.6–1.9 for different sizes of In-BC particles at 200–350 nm. When assuming the In-BC cores have a void-free BC sphere with a density of 1.8 g cm−3, the shell ⁄ core ratio and Eab could be overestimated by ∼ 13 and ∼ 17 % respectively. The new approach developed in this work will help improve calculations of mixing state and optical properties of ambient In-BC particles by quantification of changes in morphology and density of ambient In-BC cores during aging process.