Direct radiative effects of black carbon and brown carbon from Southeast Asia biomass burning with the WRF-CMAQ two-way coupled model

Black carbon (BC) and brown carbon (BrC) have been considered light-absorbing components of particulate matter and affect weather and climate. Biomass burning (BB) emission from Southeast Asia (SEA) is a key source of BC and BrC on the planet. In this study, the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) two-way coupled model was used with the Global Fire Emissions Database Version 4, to investigate the direct radiative effect (DRE) of BC and BrC in March 2015 over SEA. The Rapid Radiative Transfer Model for the Global Circulation Model was employed in the WRF-CAMQ to calculate the aerosol optical properties in 14 shortwave spectral bands. Parameterization of the light absorption property of BrC described by Saleh et al. (2014) is coded and embedded into the WRF-CMAQ. The light absorption property of BrC is determined by the BB BC to organic carbon ratio in each grid and each time step, which is more in line with the smog chamber experiments compared to the originally fixed coefficient in the model. Experiments with and without BC/BrC DRE were conducted. Preliminary results show that the monthly mean DRE from BB BC can reach 18.3 W/m² in the Indochina region and 3.0 W/m² in southern China, decreasing the surface temperature by up to 0.2 and 0.1 °C, respectively. The monthly DRE from BB BrC can reach 1.3 W/m² in the Indochina region but only around 0.1 W/m² in southern China. Meanwhile, the maximum instant DRE of BrC can reach 10.0 W/m², which is expected to exert a local synoptic scale influence.