Simulation of the Steady Mixing State of Black Carbon With a Two-Dimensional Sectional Model

Black carbon (BC) strongly absorbs solar radiation and has a warming effect on the earth-atmosphere system. BC experiences continuous aging, making its optical properties a great uncertainty due to the complex mixing state. To address this issue, we developed a sectional model which is capable of tracking both the aerosol size and the BC core size. This model was applied to simulate BC aging process. The atmospheric observational data from a slightly polluted case was employed to drive the model. It is shown that BC's characteristics tend to reach a steady state within 12 hr. Our analysis reveals that, in the steady state, the size distribution of BC-containing particles demonstrates a notable characteristic: the particle size distribution decreases exponentially as the particle size increases. This exponential relationship provides a simplified yet accurate representation of the complex BC mixing state. This steady-state size distribution of BC-containing particles is validated across diverse atmospheric conditions.