| Summary: | Nitrogen dioxide (NO<sub>2</sub>) is an essential air pollutant related to adverse health effects. A space-time neural network model is developed for the estimation of ground-level NO<sub>2</sub> in this study by integrating ground NO<sub>2</sub> station measurements, satellite NO<sub>2</sub> products, simulation data, and other auxiliary data. Specifically, a geographically and temporally weighted generalized regression neural network (GTW-GRNN) model is used with the advantage to consider the spatiotemporal variations of the relationship between NO<sub>2</sub> and influencing factors in a nonlinear neural network framework. The case study across the Wuhan urban agglomeration (WUA), China, indicates that the GTW-GRNN model outperforms the widely used geographically and temporally weighted regression (GTWR), with the site-based cross-validation R<sup>2</sup> value increasing by 0.08 (from 0.61 to 0.69). Besides, the comparison between the GTW-GRNN and original global GRNN models shows that considering the spatiotemporal variations in GRNN modeling can boost estimation accuracy. All these results demonstrate that the GTW-GRNN based NO<sub>2</sub> estimation framework will be of great use for remote sensing of ground-level NO<sub>2</sub> concentrations.
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