Measurement and analysis of the comprehensive emission intensity and coupling coordination relationship of carbon dioxide emissions and pollutant emissions in the Yangtze River Delta Urban Agglomeration

Investigating the characteristics and coupling coordination relationship of carbon dioxide (CO2) emissions and pollutant emissions at the urban-agglomeration scale, is helpful for analyzing how urbanization and the environment interact. This paper measured the comprehensive emission intensity of CO2 and pollutant emissions in the Yangtze River Delta Urban Agglomeration (YRDUA) and explored the spatiotemporal characteristics of the comprehensive emission intensity using the Theil index and cold-hot spot analysis. Further, we constructed a coupling coordination model for CO2 emissions and pollutant emissions to calculate their coupled coordination degree. The dynamic evolution trend of the coupling coordination level was examined using spatiotemporal analysis and kernel density estimation. The results showed that: (1) The comprehensive emission intensity shows a trend of first increasing and then decreasing, with a characteristic change from a "two polarization" distribution in 2011 to a "centralized" distribution in 2018 and then to a "two polarization" distribution in 2020. (2) The difference in comprehensive emission intensity across cities in the YRDUA has been decreasing and is negatively correlated with economic growth. Additionally, Tongling, Maanshan, and Jiaxing were primary hotspots of the YRDUA. (3) The trend of the coupling coordination level of CO2 and pollutant emissions showed a significant increase. The level of coupling coordination in Shanghai, Nanjing, Wuxi, Changzhou, Suzhou, Hangzhou, Ningbo, and Jiaxing was higher than in the YRDUA on average, while it was lower in other cities during the study period, indicating that there is still much room for improvement in CO2 and pollution reduction in the YRDUA.