The Situation of Global Dimming in the Regional Major Cities of Thailand: Shedding Light on a Growing Concern

The reduction in surface solar radiation known as "Global Dimming" has significant repercussions for both human and ecological well-being. There is a need for further empirical evidence to better understand the extent of Global Dimming in Southeast Asia, particularly in Thailand. This study aims to examine Surface Solar Radiation (SSR) and Aerosol Optical Thickness (AOT) trends and their relationships before the 1990s and post-1990s using ground station data and satellite images to investigate land use of five provinces: Bangkok, Chiang Mai, Songkla, Rayong, and Kon Khen. AOT does not rise significantly annually, but in the central region during the summer, it increases with a significance level of 0.05, and March is the most significant monthly change. SSRavg trend was unchanged before the 1990s. After the 1990s, SSRavg decreased significantly in the central, northern, and eastern regions, with a significance level of 0.01, especially in winter. AOT correlates positively with surface temperature and negatively with SSR intensity and relative humidity. AOT is positively correlated with built-up cover types and negatively correlated with forest cover types (R2 values of 0.708). These findings reveal that Thailand is entering a global dimming; hence, managing land cover could lessen air pollution and help future preventative efforts.