R. Macatangay, National Astronomical Research Institute of Thailand, Thailand

We have developed an experimental atmospheric forecasting system for Indochina and Southeast Asia based on WRF-Chem v. 4.1 for air quality and astronomical applications. The system's configuration has been optimized in northern Thailand based on the study by Bran et al. (submitted). Model output validation has been performed by comparing the model results with available air pollution (e.g. PM2.5 and PBL height), astronomical (e.g. seeing) and meteorological (e.g. precipitable water vapor and relative humidity) data in the region. Operation of the system started in December 2021 (corresponding to the cool dry season in Indochina when air pollution begins to increase and when the astronomical observing season peaks) up to the present. Focusing on northern Thailand, we have seen good model performance when the PM2.5 and PBL height simulations were compared to observations in December 2021, January 2022 and February 2022. However, as the air pollution peaks in March and April 2022, due to increased biomass burning, the discrepancies between the model and the observations increased. We attribute these differences from limitations in the emission inventories used (e.g. fire, anthropogenic and biogenic emissions) underestimating the sulfate and nitrate components of PM2.5. This caused incorrect aerosol-meteorology interactions overestimating the PBL height and therefore underestimating the PM2.5 mass concentrations during March and April 2022. It is therefore endeavored to improve the results by using more updated emission inventories and employing satellite aerosol optical depth data assimilation for the next steps of the system.