Filter-based absorption enhancement measurement for internally mixed black carbon particles over southern China

• Published in: The Science of the total environment Vol. 762; p. 144194
• Main Authors: Fu, Yuzhen, Peng, Xiaocong, Guo, Ziyong, Peng, Long, Lin, Qinhao, Li, Lei, Li, Mei, Chen, Duohong, Zhang, Guohua, Bi, Xinhui, Wang, Xinming, Sheng, Guoying
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 25-03-2021
• Subjects: Absorption enhancement; Aethalometer; Black carbon; Mixing state; Absorption enhancement; Aethalometer; Mixing state; Black carbon
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.144194

The effect of the mixing state of black carbon (BC) on light absorption is of enduring interest due to its close connection to regional/global climate. Herein, we present concurrent measurements of both BC absorption enhancement (Eabs) and the chemical mixing state in southern China. Eabs was obtained by simultaneous measuring the light absorption coefficient using an aethalometer before and after being heated. The observed Eabs was categorized into non- (Eabs ≤ 1.0), slight (1.0 < Eabs ≤ 1.2), and higher (Eabs > 1.2) enhancement groups, and it was compared to the mixing state of elemental carbon (EC) particles detected by a single particle aerosol mass spectrometer (SPAMS). The individual EC-containing particles were classified into four types, including EC with sodium and potassium ion peaks (NaK-EC), long EC cluster ions (Cn+/−, n ≥ 6) with sulfate (EC-Sul1), short EC cluster ions (Cn+/−, n < 6) with sulfate (EC-Sul2), and EC with OC and sulfate (ECOC-Sul). NaK-EC and EC-Sul2 are the dominant EC types. Slight enhancement group is mainly explained by the photochemical production of ammonium sulfate and organics on EC-Sul2 during afternoon hours. In contrast, the higher Eabs is primarily attributed to the enhanced mixing of ammonium chloride with NaK-EC during morning hours, without photochemistry. The characterization of source emissions indicates that NaK-EC is likely from coal combustion and is associated with a relatively higher amount of ammonium chloride. To our knowledge, this is the first report to state that EC particles associated with ammonium chloride have a relatively higher Eabs.
[Display omitted]
•Both BC absorption enhancement (Eabs) and mixing state were measured in real-time.•The morning Eabs peak is explained by primary emission.•Secondary composition contributes to the afternoon Eabs peak.•Internally mixed ammonium chloride is more responsible for the higher Eabs.