Understanding the seasonal dynamics of surface PM2.5 mass distribution and source contributions over Thailand

The escalating levels of aerosols have emerged as a significant concern for climate extremes in the Southeast Asian regions, particularly accentuated during El Nino Years. In this study, we utilized a combination of atmospheric measurements and modeling to investigate the seasonal and geographical distribution of PM 2.5 mass concentrations and its primary contributors across Thailand during La Nina (2017) and El Nino (2019) years. Our findings revealed the highest daily mean surface PM 2.5 mass concentration during the summer season across most regions, followed by winter, and the lowest levels during the rainy season. Notably, a significant shift in daily mean PM 2.5 mass was observed from 2017 to 2019 across all seasons, with a pronounced increase of 70.9% over northern Thailand during the summer, attributed to heightened biomass burning (BB) contributions. In terms of source attribution for PM 2.5 mass, the primary contributors in 2017 were BB at 34.3%, followed by anthropogenic emissions (AE) at 32.4%, and natural emissions (NE) at 30.1%. However, in 2019, the BB contribution surged to 47.4% nationwide. During El Nino years, BB played a significant role in shaping concentrations during summer and winter, while NE dominated the rainy season. An important implication of our findings is the significant potential for reducing daily and annual mean PM 2.5 mass levels throughout Thailand by effectively reducing BB emissions.