The dynamic characteristics of multi-media carbon pollution and their spatial influencing factors: A case study of the Greater Bay Area of China

For urban agglomerations that contain multiple interconnected cities, carbon pollution mitigation is particularly challenging due to the complex pollution transfer among environmental media and among cities. Insufficient attention has been paid to the city-level metabolic processes of carbon in diverse physicochemical forms and their spatial interactions, impeding the identification and management of multi-media carbon pollution from the integrated perspective of the whole urban agglomeration. Using the Greater Bay Area of China as a case, this study reveals the dynamic characteristics and spatial influencing factors of multi-media carbon pollution covering 30 consecutive years based on substance flow analysis and a spatial econometric model. We find increasing necessity for controlling carbon pollution in the solid state, which reached 1890 Gg C/a in 2018 and was significantly higher than that in the gaseous (290 Gg C/a) and liquid (730 Gg C/a) state. Cross-media transfer of carbon pollution made an increasingly substantial contribution to total carbon pollution from 14.6% to 20.7%, stressing the need for treatment and harmless disposal of sludge and the control of CH₄ produced from waste landfilling, wastewater treatment, and livestock manure. Relocation of heavily polluting industries and variances at the level of environmental regulation between cities causes spatial transfer of carbon pollution, while the improvement of industrial structure and the advancement of pollution treatment technology have a positive demonstration effect for carbon pollution abatement of the neighboring cities. This study demonstrates the necessity of multi-media and multi-city integrities in carbon pollution mitigation within clustered cities.