Key drivers to heterogeneity evolution of black carbon-containing particles in real atmosphere

The evolution of black carbon (BC) particles during atmospheric aging led to the complexity of their environmental and climate effect assessment. This study simultaneously measured the heterogeneous distribution of multi-level microphysical properties of BC-containing particles (i.e., BC mass concentration, coating amounts, and morphology) by a suite of state-of-the-art instruments, and investigated how atmospheric processing influence these heterogeneities. Our field measurements show that the mixing states of atmospheric BC-containing particles exhibit a clear dependence on BC core diameters. The particles with small BC core sizes (80-160 nm) are coated and reshaped more rapidly in real atmosphere, with coating-to-BC mass ratios (M_R) and non-spherical fractions of 5.1 ± 1.2 and 61 ± 19 %, respectively. Conversely, the particles with large core sizes (240-320 nm) are thinly coated and fractal, with M_R and non-spherical fractions of 4.0 ± 0.3 and 74 ± 15 %, respectively. Furthermore, primary emissions result in low heterogeneity in coating amount but great heterogeneity in morphology between BC-containing particles of different sizes, while photochemical processing would enhance heterogeneity in coating amount but weaken the heterogeneity in morphology. Overall, our field measurement of multi-level microphysical properties highlights that BC core size and atmospheric processing are the key factors that drive the heterogeneity evolution of BC-containing particles in real atmosphere.