Disparate evolution mechanisms and optical absorption for transboundary soot particles passing through inland and sea pathways

Abstract. Soot particles, as a type of warming aerosols, play a critical role in climate warming. During transport, these particles undergo atmospheric condition-dependent aging processes that influence their microphysical and optical properties. Here, we investigated the variations in morphology, mixing states, sizes, and optical absorption of soot-containing particles and further revealed their evolution mechanisms during two distinct transboundary transport through the inland and sea pathways. Comparing transboundary soot-containing particles transported through the inland and sea pathways, we found more soot cores in the latter individual particles, although their dominant mixing states exhibited a similar transition from partly-coated at 62–67 % by number to embedded structures at 71–72 %. The core-shell size ratio (D_p/D_c) and soot core fractal dimension of embedded soot-containing particles transported through the sea pathway were both greater compared to the inland pathway. These differences were attributed to distinct evolution mechanisms experienced by soot-containing particles during transport: heterogeneous aging processes through the inland pathway and cloud processes through the sea pathway. Optical simulation showed amplified light absorption of soot-containing particles during their transboundary transport. Furthermore, the radiative absorption amplification per unit D_p/D_c change reduced by 72 % due to the entrainment of multiple soot cores within individual particles following the transport pathway change from the inland to the sea. This study suggests varied mixing configurations and radiative absorption of transboundary soot-containing particles driven by different environmental conditions and highlights the necessity of incorporating multicore black carbon mixing structures into climate models.