Assessment the Aging Process and Radiative Impact of Black Carbon in the Two-Way Coupled WRF-CMAQ Modeling System

A two-way coupled meteorology-chemistry model (WRF-CMAQ) with developing and implement the BC aging module was employed to simulate the aging process and radiative impacts of black carbon (BC). In order to improve the estimation of BC radiative impact, the BC aging module was developed based on aerosol microphysics mechanisms. The resulting aging rate of fresh BC was around 5 hours with strong vertical and diurnal variations which was higher in polluted area. The biases in simulated light absorption by BC were reduced from 134% to 55% after implement the aging module into the model which significantly improve the simulation performance of the BC radiative impacts. Meanwhile, the significantly weaker wet scavenging and enhanced BC were found from the BC aging process, compared to the default CMAQ with internal mixing state.

The large emission of sulfate-nitrate and secondary organic aerosol precursors resulted in the higher aging rate through condensation and coagulation. However, during some heavy pollution episodes in China, organics or nitrates dominates over sulphate and become the major component of the coating material. Hence, future studies on the BC aging from OM and nitrate will be conducted based on the currently BC aging module. Based on available in situ measurements for BC particles, the parameterization of BC aging process and then comprehensive assessment of the radiative impact on air quality and climate change of black carbon is conducted together with modeling study, considering the size distribution, hygroscopicity, morphology and mixing state of BC-containing particles. Application of our newly developed parameterization of fixed BC aging module to online WRF-CMAQ model will provide more reliable estimates of the spatial distribution of BC and radiative effects at regional scale.