Effects of Aerosol Radiative Feedback during a Severe Smog Process Based on WRF-Chem Simulations

The effects of aerosol-radiation feedback on meteorology and air quality over eastern China during a severe smog event in December 2013 are simulated using the fully coupled online Weather Research and Forecasting/Chemistry model. Three simulation scenarios that include different aerosol configurations are applied to distinguish aerosol radiative effects. Results of these experiments indicate that the simulated shortwave radiation at the surface, 2 m temperature and planetary boundary layer (PBL) height all reduce over the polluted areas during the smog event due to direct, semi-direct, and indirect radiation effects of aerosols. A lower PBL height is unfavorable for the dispersion of water vapor and pollutants, which makes the fog structure more stable and deteriorates the smog event. Furthermore, the aerosol radiation effects (direct, semi-direct and indirect effect) prolong the duration of the smog event and the pollutants can reach higher levels. Looking at the chemical species, it is found that the aerosol direct and semi-direct radiation effects lead to increases in PM_2.5 concentration, extinction coefficients, NO_x concentration and decreases in O₃ concentration; meanwhile, the aerosol indirect radiation effect further increases PM_2.5 concentrations and extinction coefficient but decreases NO_x and O₃ concentration. In general, the aerosol radiative effects deteriorate the air pollution event by promoting the development of smog.