我国社会经济发展和生态文明建设面临着两大目标约束：碳达峰碳中和目标与美丽中国目标，需要深入推进温室气体治理与环境质量改善。减污降碳协同增效是兑现碳中和承诺和深入打好污染防治攻坚的总抓手，需要充分利用大气污染物与温室气体之间、各类温室气体之间、以及各类政策之间的协同效应，科学高效地实现碳达峰碳中和目标与美丽中国目标。首先，本文研究了大气污染治理对温室气体减排的协同效益。本文首先构建了企业减排策略的理论模型，并在此基础上进行了实证研究。本文利用环境保护“十一五”规划作为准自然实验，基于企业层面污染用能数据与手工收集的市级SO2减排目标数据，评估了二氧化硫排放治理对二氧化碳排放的溢出影响。大气污染治理可以显著降低温室气体排放，大气污染治理对温室气体减排具有明显的协同效益。并且，随着大气污染治理的深入推进、末端治理减排潜力收窄，源头治理对污染减排的作用增大，大气污染治理的协同效益增加。其次，本文研究了二氧化碳与非二氧化碳温室气体协同治理效益。本文基于可计算一般均衡模型，通过比较不同的温室气体治理方式，对二氧化碳与非二氧化碳温室气体协同治理的长期一般均衡影响与社会经济效益进行模拟分析。研究发现，在实现同样的温室气体减排量的情况下，二氧化碳与非二氧化碳温室气体共同治理会降低温室气体治理的边际成本和温室气体减排的经济损失，并且会对不同行业产生异质性影响。最后，本文对政策间的协同效应进行了理论分析与实证研究。本文通过理论模型与实证计量分析，从源头治理与末端治理两方面研究了气候能源政策与大气环境政策之间、不同类型环境政策之间的交互作用和叠加影响。研究发现，多个政策的组合效果并非各个政策独立影响的简单相加：不同类型政策间的相互作用会限制其中约束相对较弱一方的政策影响，并且这种限制作用在不同政策组合下的表现不同，这主要体现在对源头治理与末端治理的影响存在差异。基于本文研究结果，我们从减污降碳协同增效的治理路线、多温室气体协同治理措施、气候能源政策与大气环境政策协同治理方式等方面提出政策建议。

Climate change and air pollution are two major issues of China’s economic development and ecological civilization construction. It is necessary to further promote greenhouse gas (GHGs) governance and environmental quality improvement. The synergistic effect of pollution reduction and carbon reduction is the overall starting point for fulfilling the commitment to carbon neutrality and in-depth pollution governance. It is critical to make full use of the relationship between air pollutants and greenhouse gases, between types of greenhouse gases, and between various policies. The synergistic effect is crucial to scientifically and efficiently realize the goal of carbon neutrality and the goal of beautiful China.First, this paper studies the co-benefits of air pollution control on greenhouse gas emission reduction. This paper first constructs a theoretical model and then conducts an empirical study. Leveraging the "11th Five-Year Plan" of environmental protection as a quasi-natural experiment, this paper evaluates the spillover impact of SO2 emission regulation on CO2 emissions based on firm-level data and manually collected SO2 reduction targets. To solve the endogeneity of SO2 reduction targets, we use "critical load of sulfur deposition" as an instrumental variable. We find that air pollution regulation can significantly reduce CO2 emissions and thus has obvious synergistic benefits for GHGs reduction. Moreover, with the in-depth advancement of air pollution control and the narrowing of the emission reduction potential of terminal treatment, the effect of source control on pollution emission reduction raises, and the synergy benefits of air pollution control increase.Second, this paper studies the benefits of collaborative governance of CO2 and non-CO2 GHGs. Based on the computable general equilibrium (CGE) model, this paper simulates and analyzes the general equilibrium impact and social and economic benefits of the collaborative governance of CO2 and non-CO2 GHGs by comparing different climate policies. We find that achieving the same GHGs reduction, the co-governance of CO2 and non-CO2 GHGs will reduce the marginal cost and overall economic loss of GHGs reduction, and have heterogeneous impacts on different industries.Finally, this paper conducts theoretical analysis and empirical research on the synergy between policies. Through theoretical models and empirical econometric analysis, this paper studies the interaction effects between climate (energy) policy and atmospheric environment policy, and between different types of environmental policies. The study found that the combined effect of multiple policies is not a simple summation of the independent effects of each policy: the interaction between different policies will limit the policy impact of one with relatively weak constraints. And the dominant effect is different under different policy combinations regarding “source governance” and “end-of-pipe treatment”.Based on the research results of this paper, we put forward policy suggestions from the aspects of synergistic governance routes of pollution and GHGs, multi-greenhouse gas collaborative governance measures, coordinated governance methods of climate energy and atmospheric environment policy, and so on.