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DOI	10.5194/acp-20-9701-2020
	The absorption Ångstrom exponent of black carbon with brown coatings: Effects of aerosol microphysics and parameterization
	Zhang X.; Mao M.; Yin Y.; Tang S.
发表日期	2020
ISSN	16807316
起始页码	9701
结束页码	9711
卷号	20 期号:16
英文摘要	The aerosol absorption Ångstrom exponent (AAE) is a crucial optical parameter for apportionment and characterization. Due to considerable inconsistences associated with observations, numerical research is a powerful means to give a better understanding of the AAE of aged black carbon (BC) aerosols. Numerical studies of the AAE of polydisperse BC aggregates with brown coatings using the exact multiple-sphere T-matrix method (MSTM) are performed. The objective of the study is to thoroughly assess the AAE of coated BC influenced by their observation-based detailed microphysics and then provide a new AAE parameterization for application. At odds with our expectations, more large-sized BC particles coated by thin brown carbon can have an AAE smaller than 1.0, indicating that BC aerosols internally mixing with brown carbon can even show lower AAE than pure BC particles. The AAE of BC with brown coatings is highly sensitive to the absorbing volume fraction of the coating, coated volume fraction of BC, shell / core ratio, and particle size distribution with a wide variation, whereas the impacts of BC geometry and BC position within the coating are negligible. The AAE of BC with brown coatings can be larger than 3.0 if there are plenty of small-sized coated BC particles, heavy coating, or a large amount of brown carbon. However, the AAE of BC with non-absorbing coating appears to be weakly sensitive to particle microphysics with values around 1.0 (i.e., 0.7-1.4), suggesting the substantial role of the absorbing volume fraction of the coating in AAE determination. With more realistic BC geometries, our study also indicates that the occurrence of brown carbon may not be confidently determined unless AAE < 1.4. The currently popular core-shell Mie model reasonably approximates the AAE of fully coated BC by brown carbon, whereas it underestimates the AAE of partially coated or externally attached BC and underestimates more for a lower coated volume fraction of BC. In addition, we present a parameterization of the AAE of coated BC with a size distribution on the basis of numerical results, which can act as a guide for the AAE response to the absorbing volume fraction of the coating, coated volume fraction of BC, and shell / core ratio. The proposed parameterization of coated BC AAE generates a decent prediction for moderate BC microphysics, whereas caution should be taken in applying it for extreme cases, such as externally attached coated BC morphology. Our findings could improve the understanding and application of the AAE of BC with brown coatings. © Author(s) 2020.
语种	英语
scopus关键词	absorption; aerosol; aggregate; black carbon; brown carbon; matrix; numerical model; parameterization; particle size; size distribution
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/143930
作者单位	Key Laboratory of Meteorological Disaster, Ministry of Education (KLME), Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD), Joint International Research Laboratory of Climate and Environment Change (ILCEC), Earth System Modeling Center (ESMC), Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science and Technology, Nanjing, 210044, China; School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing, 210044, China; National Satellite Meteorological Center, China Meteorological Administration, Beijing, 100081, China
推荐引用方式 GB/T 7714	Zhang X.,Mao M.,Yin Y.,et al. The absorption Ångstrom exponent of black carbon with brown coatings: Effects of aerosol microphysics and parameterization[J],2020,20(16).
APA	Zhang X.,Mao M.,Yin Y.,&Tang S..(2020).The absorption Ångstrom exponent of black carbon with brown coatings: Effects of aerosol microphysics and parameterization.Atmospheric Chemistry and Physics,20(16).
MLA	Zhang X.,et al."The absorption Ångstrom exponent of black carbon with brown coatings: Effects of aerosol microphysics and parameterization".Atmospheric Chemistry and Physics 20.16(2020).