Spatial-temporal heterogeneity of carbon dioxide concentration in Beijing, Tianjin, and Hebei based on interpretable theory

Abstract

With rapid urbanization, the Beijing-Tianjin-Hebei (BTH) region has experienced intensifying greenhouse effects due to increases in global carbon dioxide (CO₂) concentrations. Therefore, studying the spatial and temporal heterogeneity of CO₂ concentrations and understanding the causes of regional climate change have become crucial. Although previous studies have focused on calculating regional carbon sources and sinks, explicit and directly interpretable analyses targeting CO₂ concentrations per se remain limited. Based on multi-source satellite data, this study systematically analyzed changes in the spatiotemporal distribution of CO₂ concentrations in the BTH region and its dynamic relationship with environmental factors from 2003 to 2021 using long short-term memory network and interpretability theory models. The results showed that CO₂ exhibits a high value area with spatiotemporal flux that shifts from northwest to southeast and has a seasonally fluctuating growth rate of 2.29 ppm/year. Nightlight (NTL) data were highly correlated with the CO₂ concentration (0.98), whereas the correlation coefficient between the two centers of gravity was 0.57, indicating a moderate effect on CO₂ concentration increases and spatial changes. Moreover, the normalized vegetation index (NDVI) (0.92) was most strongly correlated with interannual changes in CO₂, followed by precipitation (0.51), temperature (0.44), and solar radiation (0.14), and the contributions of diurnal variations in these parameters to the spatiotemporal characteristics of CO₂ are ordered temperature (6.79) > NDVI (6.36) > solar radiation (2.20) > precipitation (1.66). Overall, this study enhances our understanding of the spatiotemporal characteristics of CO₂ concentrations in the BTH region and reveals the driving effects of different factors, especially with regard to natural factors that present nonlinear change characteristics. Moreover, our findings have theoretical and practical significance for reducing CO₂ concentrations and mitigating greenhouse effects in the BTH region and other industrial city clusters.