Surface PM2.5 mass concentrations during the dry season over northern Thailand: Sensitivity to model aerosol chemical schemes and the effects on regional meteorology

Biomass burning emissions (agriculture and forest) are one of the major contributors to air pollution over Thailand during the hot-dry season (March-April) and aerosols from biomass burning can adversely affect the weather and produce health effects (respiratory disease, heart disease etc.). The present study investigated the sensitivity of aerosol chemistry schemes (Goddard Chemistry Aerosol Radiation and Transport, GOCART; Model for Simulating Aerosol Interactions and Chemistry, MOSAIC) on spatio-temporal distributions of simulated PM2.5 (particle sizes <2.5 mu m) mass concentrations. Also, the study looked into the impact of PM2.5 on meteorology during an intense biomass burning period (15 March - 15 April 2019) using an online regional chemical transport model, Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). PM2.5 mass concentrations were observed over the northern regions of Thailand varying from 40 to 240 mu g m- 3. The simulations using GOCART and MOSAIC aerosol scheme were able to capture the spatio-temporal variations of PM2.5 mass concentrations in general. However, it underestimated the observation magnitudes by about 24% and 27%, respectively. In addition, the sensitivy of EDGAR-HTAP (Emission Database for Global Atmospheric Research collaboratively with the task force for Hemispheric Transport of Air Pollution) and CAMS-GLOB-ANT (Copernicus Atmosphere Monitoring Service Global) anthropogenic emission inventories on PM2.5 mass were investigated using the model. The simulated aerosol mass concentrations from EDGAR-HTAP found more realistic emissions when compared to CAMS-GLOB-ANT in most of the regions. The discrepancy in the simulation of aerosol mass concentrations could be attributed to uncertainties in the emission inventories, weak representation of secondary aerosol compositions, as well as the overestimation of wind speed and wet scavenging in the model. The study also investigated the influence of aerosols on meteorology by comparing a simulation with aerosolradiation-interaction to a simulation without aerosol-radiation-interaction in the atmosphere during the time period. Significant changes in meteorological parameters were observed over regions having higher aerosol mass concentrations with a reduction of about 26% in solar insolation, 3.9% in near surface temperature, 21% in planetary boundary layer height and an increase of 13% in relative humidity.