This study examines tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) over Thailand using ground-based Pandora observations in Bangkok and S5P/TROPOMI satellite data at the national scale. Pandora measurements reveal distinct diurnal and weekly cycles, with sharp rush-hour peaks and lower weekend values, reflecting strong anthropogenic influence. Monthly and seasonal analyses show that NO2 is highest in winter and lowest during the monsoon, influenced by the height of the boundary layer, precipitation, and photolysis rates. A comparison of Pandora and S5P/TROPOMI monthly averages shows strong temporal agreement while revealing a consistent low bias in S5P/TROPOMI. A seasonal breakdown shows the highest agreement in summer, moderate agreement in winter, and the poorest performance during the rainy season. At the national scale, the highest NO2 levels are concentrated in central Thailand, especially Bangkok (5.59 × 1015 molec/cm2). Elevated column amounts also appear across the Bangkok Metropolitan Region and the Eastern Economic Corridor, consistent with urban–industrial sources, while Lampang exhibits a distinct hotspot associated with emissions from the Mae Moh power plant. The seasonal variation of aerosol optical depth (AOD) also follows the NO2 pattern, with high AOD corresponding to elevated NO2 levels during winter in central Thailand and during summer in northern Thailand. In contrast, both AOD and NO2 decrease substantially during the rainy season due to enhanced wet deposition and more efficient atmospheric cleansing. These results highlight the dominant influence of traffic, industry, and power generation on Thailand's NO2 burden.
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