The effects of necking on the optical properties of coated black carbon aggregates

Necking substantially improves the representation of black carbon (BC) morphology. However, recent studies placed more focused on bare BC particles and overlooked that the realistic BC emitted from biomass burning are often thickly coated. This paper investigates the effect of necking on the coated BC optical properties and applies the modified cylindrical connector model for necking and the parameter-tunable algorithm for coating. Results indicate that necking enhances the scattering matrix elements, and its effect increases with coating thickness and fractal dimension. Necking contributes a 10 %–30 % increase in absorption and scattering cross-sections, which is crucial for assessment of the radiative effects of the BC fraction in wildfire smoke. Additionally, necking provides a better explanation for high linear depolarization ratios observed in wildfire smoke. For low fractal dimension cases, necking reduces the lidar ratio. Conversely, necking has a minimal influence on single-scattering albedo.