Achieving the “Dual Targets” of CO2 emission reduction and air quality improvement for Chinese cities

China is facing the challenges of both climate change and air pollution. To tackle the challenges, China has set specific goals, such as the CO2 emission peak target by 2030 and the "Beautiful China" target by 2035, to reduce greenhouse gases and air pollutant emissions. Cities in China play an important role as they are the fundamental units to implement reduction policies. In this dissertation, we investigate the pathway for Chinese cities to achieve the dual targets of CO2 emission reduction and air quality improvement. This work is divided into the following five chapters: an overview (Chapter 1), three chapters of original research (Chapters 2 – 4), conclusions and future work (Chapter 5).We first make a comprehensive assessment of air quality and CO2 emission changes from 2015 to 2019 for 335 Chinese cities, using the city-level data of PM2.5 and O3 concentrations and CO2 emissions. We select important regions for air pollution control in China and categorize all cities into different classes according to their development levels. Then we compare the changes of air quality and CO2 emission by region or city class. We find that PM2.5 concentrations decrease remarkably from 2015 to 2019 due to mandatory city-level PM2.5 reduction targets, especially in the Beijing-Tianjin-Hebei and Yangtze River Delta regions. Nonetheless, O3 concentrations increase in 91% of Chinese cities and CO2 emissions increase in 69% of the cities. The changes in CO2 emissions are significantly lower in developed cities compared to developing cities, which is mainly driven by the reduction in energy intensity and the improvement in energy structure. Our findings indicate a lack of synergy in air quality improvement and CO2 emission reduction in China under the current policy framework. To tackle the challenges of both air pollution and CO2 mitigation, we suggest that cities set mandatory city-level CO2 emission reduction targets and reinforce energy-related measures in future policies. To address the inconsistency in current CO2 and air pollutants emission inventories, we then develop a unified emission inventory including both emissions. We also identify the co-hotspots of both CO2 and air pollutants emissions at a high spatial resolution (1 � 1 km2). Using Guangzhou city as a case, we find that the stationary combustion sector and the transportation sector are the main contributors to CO2 and air pollutants emissions, together accounting for 95%, 67%, and 93% of total CO2, SO2, and NOx emissions. The co-hotspots analysis shows that more than 66% of total CO2 and air pollutants emissions are originated from the top 10% emission grids. Our findings enable accurate identification of high-emission grids, which improve the precision and effectiveness in the collaborative control of CO2 and air pollutants. Lastly, we propose a pathway for Chinese cities to reach the dual targets of CO2 emission reduction and air quality improvement. Using Yantai city as a case, we develop an integrated assessment model that couples the emission projection, air quality, and health assessment. We find that strict energy-related measures can help Yantai meet the national annual PM2.5 standard of 35 �g/m3 by 2030 and achieve the carbon neutrality goals by 2060. Energy-related measures contributed to 53% and 79% of PM2.5 reduction in 2035 and 2060, exhibiting an increasing potential in improving air pollutants emissions compared to the advanced end-of-pipe controls. We find that the future health benefit from improved air quality will likely compensate for the abatement cost of implementing energy measures, with a net monetized benefit of 1.9 billion Chinese yuan in 2060. Our findings could provide a reference for Chinese cities to deal with the dual challenges in the future. Overall, we find a lack of synergy in air quality improvement and CO2 emission reduction in China under the current policy framework. The unified emission inventory and co-hotspots analysis provide a basis to design collaborative control strategies. The proposed dual targets pathway can guide Chinese cities to address both challenges in future policy design