Absorption enhancement and shielding effect of brown organic coating on black carbon aerosols

Abstract

This study explores how the mixing structures and coating compositions of black carbon (BC) particles influence their light absorption, focusing on liquid-liquid phase separation (LLPS), which separates organic and inorganic phases and redistributes BC from the inorganic core (Icore) to the organic coating (Ocoating). Using transmission electron microscopy and 3D-modeling, we found that the BC core’s position significantly impacts its light absorption. A BC core embedded within the Icore shows stronger light absorption at wavelengths below 600 nm compared to the same core in the Ocoating. When Ocoating is considered as brown carbon (BrC), it reduces BC core’s light absorption at 350 nm due to shielding effect, but its overall impact on the entire BC particle is minimal (–3.0% ± 1.6%). The result indicates that in LLPS particles, the BrC coating primarily enhances light absorption, emphasizing the need to consider both mixing structures and coating compositions of BC in atmospheric models.