Modeling simulation of aerosol light absorption: the impact of mixing state and aging process

Black carbon has an important effect on global climate change. Uncertainty surrounding the absorption property of BC-containing aerosols still exists. In this study, the optical property of PM_2.5 in Beijing in November 2018 was investigated using Mie theory based on observed and simulated PM_2.5. The results showed that the  absorption coefficient under uniform internal mixing is the highest, followed by core-shell mixing and calculation for external mixing is the lowest. The calculated BC absorption at 630 nm under a mixed mixing state (fraction of internal mixing constraint by observation) was reasonably close to the measured mean value. The simulations of the NAQPMS reproduced the temporal distribution of PM_2.5 and its components in Beijing well. Under the same mixing state, the absorption coefficient can be highly impacted by the simulation of PM_2.5 components. The aging process of BC can be reproduced by advanced microphysical module (APM) in NAQPMS. Then the fraction of aged BC can be used as a proxy for internal mixing proportion, and the absorption coefficient was reasonably reproduced. This study will provide a reference for the three-dimensional model simulation of black carbon aerosol radiation effect.