[Estimation of Near-surface NO₂ Concentration in Guangdong Province Based on Catboost Model]

Nitrogen oxide （NO_x） is an important air pollutant in the atmosphere, and nitrogen dioxide （NO₂） is one of its main components. The monitoring and estimation of NO₂ concentration is very important for environmental protection and public health. The near-real-time nitrogen dioxide concentration data （NRTI NO₂）, ERA5 meteorological reanalysis data, and DEM data provided by Sentinel-5P atmospheric pollution monitoring satellite were used as estimation variables to estimate the near-surface NO₂ concentration in Guangdong Province based on the Catboost model. The results showed that： ① The Catboost model estimated the near-surface NO₂ concentration with the highest accuracy, with the coefficient of determination （R²）, root mean square error （RMSE）, and mean absolute error （MAE） of the model fit reaching 0.91, 4.89 μg·m^-3, and 3.45 μg·m^-3 and the cross-validated R², RMSE, and MAE reaching 0.90, 4.91 μg·m^-3, and 3.43 μg·m^-3, with good stability on the monthly and quarterly scales. ② The monthly average NO₂ concentration near the surface of Guangdong Province showed a U-shaped trend, with the highest value of 43.8 μg·m^-3 in January and the lowest value of 14.37 μg·m^-3 in July. The seasonal distribution of the near-surface NO₂ concentration was characterized by "high during winter and low during summer and transitional during spring and autumn," and the NO₂ concentration in each season was in the following order： winter （27.53 μg·m^-3） > spring （20.77 μg·m^-3） > autumn （18.77 μg·m^-3） > summer （14.85 μg·m^-3）. ③ From a spatial distribution perspective, areas with high near-surface NO₂ values in Guangdong Province were mainly located in rapidly developing and densely populated areas, while areas with low values were mainly distributed in areas focusing on port economy, agriculture, and new energy sources.