Three-Dimensional Structural and Diurnal Dynamics of NO2 and HCHO by UAV Hyperspectral in Bangkok.

Fine-scale characterization of urban air pollution remains constrained by observational limitations. Here we used UAV-based hyperspectral remote sensing to conduct multitemporal and multialtitude measurements in Bangkok. High-temporal-resolution observations resolve pronounced diurnal signatures of traffic emissions: NO2 peaks in the morning under stable boundary layer conditions, whereas HCHO peaks in the afternoon, consistent with secondary photochemical production. At 100 m resolution, UAV measurements capture sharp spatial gradients and resolve localized concentration enhancements, enabling precise identification of pollution hotspots. Three-dimensional observations further show that vertical variability is not governed by simple attenuation but by structural reorganization: NO2 decreases rapidly with altitude, accompanied by strong gradient damping, whereas HCHO maintains coherent spatial patterns across height. This contrast indicates distinct three-dimensional organization regimes for primary and secondary species. By simultaneously delivering high temporal, spatial, and vertical resolution, UAV observations provide unprecedented constraints on fine-scale urban pollution structure. These results establish UAV platforms as an effective complementary tool for three-dimensional atmospheric monitoring and for constraining urban atmospheric chemistry models.