Simulated impacts of direct radiative effects of scattering and absorbing aerosols on surface layer aerosol concentrations in China during a heavily polluted event in February 2014

We quantified aerosol direct radiative effects on surface layer concentrations of aerosols during a heavily polluted event in the North China Plain (NCP, 35.4 degrees N-41.2 degrees N, 113.3 degrees E-119.3 degrees E) during 21-27 February 2014, using the chemistry version of the Weather Research and Forecasting (WRF-Chem) Model. Comparisons of model results with observations showed that the WRF-Chem model reproduced the spatial and temporal variations of meteorological variables reasonably well, but overestimated average PM2.5 concentration by 21.7% over the NCP during 21-27 February. The simulated direct radiative effects of total, absorbing, and scattering aerosols reduced the planetary boundary layer (PBL) heights by 111.4m, 35.7m, and 70.7m, respectively, averaged over NCP and 21-27 February. The direct radiative effects of total aerosols induced increases in aerosol concentrations by 11.5% for SO42-, 29.5% for NO3-, 29.6% for NH4+, 28.7% for organic carbon (OC), 26.7% for black carbon (BC), and 20.4% for PM2.5, respectively, averaged over the NCP during 21-27 February 2014. The increase in PM2.5 concentration averaged over the NCP and the haze event was 29.6g m(-3) (16.8%) due to radiative effect of scattering aerosols, as a result of the decreases in PBL height and changes in secondary aerosol production rates. The corresponding increase in PM2.5 concentration owing to absorbing aerosols was 2.1g m(-3) (1.0%), resulting from the offsetting impacts of changes in PBL height, wind near the surface, and chemical processes.