County-Level Synergy Analysis Between Air Pollution and CO2 Emissions

Cities in the air pollution transmission corridor of Beijing-Tianjin-Hebei, also known as the "2 + 26" cities, face considerable challenges regarding air pollution control and carbon reduction (APCR). However, few studies have explored the county-level synergy between CO2 emissions and air pollution. In this study, we take 327 counties in the "2 + 26" cities as the study area, introduce bivariate and trivariate synergistic indicators (BSI and TSI) to quantify the synergistic characteristics of air pollution and CO2 emissions from 2016 to 2019, and comprehensively analyze their spatial variation and aggregation characteristics. The results revealed that: (1) The annual average concentration of PM2.5 in counties under the jurisdiction of municipalities and provinces has a downward trend year by year, while the annual average concentration of O-3 continues to increase, and the total amount of CO2 emissions continues to rise. (2) The number of counties with significant PM2.5-O-3 synergies increased considerably from 2016 to 2019, whereas more than 95% of the counties in Beijing and Tianjin showing large low-value aggregation areas of BSICO2-PM2.5 and low-value aggregation areas of BSICO2-O3. (3) In each year from 2016-2019, more than 64% of counties have TSI values less than 2, the average TSI value of counties fluctuates, and changes between 1.83-2, and the distribution of high-value aggregation areas of TSI values is also more dispersed, all of which reflect the characteristics of the weak trivariate synergistic effect in the counties. The results furnish empirical data and policy recommendations for the synergistic governance of APCR at the county level.