Physicochemical Properties and Aging Behavior of Black Carbon across Emission Sources Determined by Char and Soot Subgroups

The physicochemical properties and atmospheric aging behavior of black carbon (BC) are critical for assessing its climatic impact, yet how these vary across emission sources remains poorly understood. Here, the relationship between the microphysical properties and aging processes of BC subgroups (Char and Soot) from major emission sources, including biomass burning (BB), diesel vehicle exhaust (DV), and industrial coal combustion (ICC) were investigated at single particle level. Our results revealed that BB emissions contained 84 ± 5% Char, significantly higher than DV/ICC sources (17-30%). The monomer diameter (d_m) and graphitic interplanar spacing of BB-derived BC were twice of those DV- and ICC-derived BC, and the aggregate diameter (d_a) and O/C ratio were approximately 10-fold higher, along with a weaker degree of necking. Based on the high-time-resolution sampling analysis of BB processes, we found that lower combustion efficiency favored Char formation, resulting in the increasing of d_m, d_a, and O/C ratio of BC particle. Moreover, under equivalent aging, Soot-dominated DV-BC aggregates grew 50% in d_a versus only 2% for Char-dominated BB-BC. This work demonstrates that the proportion of Char and Soot determine BC's physicochemical properties and aging behavior in different sources, emphasizing the need for subgroup-specific parametrizations in climate models.