S. Ha, MMM/NCARa

This talk introduces a new chemistry option implemented in the Weather Research and Forecasting model data assimilation (WRFDA) system coupled with the WRF-Chem model (Version 4.3.1) to activate aqueous chemistry (AQCHEM) for the assimilation of surface particulate matter (PM) concentrations. The gas-phase mechanism used is the Regional Atmospheric Chemistry Mechanism (RACM), while the inorganic aerosols are treated with the Modal Aerosol Dynamics Model for Europe (MADE), and secondary organic aerosol (SOA) production is parameterized based on the Volatility Basis Set (VBS) approach. The "RACM-MADE-VBS-AQCHEM" scheme used in the weakly coupled data assimilation system facilitates aerosol-cloud-radiation-precipitation interactions through analysis and forecast cycling, accounting for both direct and indirect aerosol effects in the short-term air quality prediction. The new implementation in the three-dimensional variational data assimilation (3D-Var) system was tested with the assimilation of PM2.5 and PM10 concentrations on the ground over the East Asian region through month-long cycling in Spring 2019. It is demonstrated that the use of aqueous chemistry in both analysis and forecast reproduces aerosol wet removal processes in association with the development of clouds, systematically changing the atmospheric composition. The new option with aqueous chemistry in WRFDA is particularly beneficial in air quality forecasting in cloudy conditions, while the simulations without aqueous chemistry overestimate surface PM10 (PM2.5) by a factor of 10 (3).