Chemical weather forecast over the Yangtze River Delta region: Application of WRF-Chem

An operational system was built based on WRF-Chem model for the chemical weather forecast over the Yangtze River Delta (YRD) region. WRF-Chem is a fully coupled `online´ regional chemistry/transport model jointly developed by the National Center for Atmospheric Research (NCAR), National Oceanic and Atmospheric Administration (NOAA) etc. The model includes on-line calculations of dynamics, transport, dry and wet deposition, gas-phase and aerosol chemistry, radiation and photolysis, and surface emissions. The Streets emission inventory was implemented and fined in resolution by using TM (Thematic Mapper) land-use data. For the application, the model was updated by introducing the effect of aerosol on photolysis due to the high aerosol concentration over the YRD region. The operational system supplies regional distribution and station temporal variation products including O3, SO2, NOx (NO, NO2), CO, volatile organic compounds (VOCs) and aerosol (PM10, PM2.5, EC) etc. The observational data at five sites over Shanghai was used to evaluate the performance of the system. The results show that 1) the introduction of aerosol effect on photolysis distinctly increases ozone forecast, and 2) the numerical forecast has good performance in both concentration and temporal variability of ozone and aerosol, although it needs to be improved for very high concentration episodes. The operational system will greatly benefit the chemical weather forecast over the YRD region.