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

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 (E-abs) and the chemical mixing state in southern China. E-abs was obtained by simultaneous measuring the light absorption coefficient using an aethalometer before and after being heated. The observed E-abs was categorized into non- (E-abs <= 1.0), slight (1.0 < E-abs <= 1.2), and higher (E-abs > 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 (C-n(+/-), n >= 6) with sulfate (EC-Sul1), short EC cluster ions (C-n(+/-), 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 E-abs 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 E-abs. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The mixing state of black carbon (BC) has a significant impact on light absorption and is closely related to regional/global climate. Different levels of BC absorption enhancement are associated with specific chemical mixing states, such as the presence of ammonium chloride with NaK-EC leading to higher light absorption. Understanding the sources and characteristics of EC particles can provide insights into the mechanisms of light absorption.