Spillover Effects: Evidence from Air Pollution Levels under Low-Carbon City Pilot Policies

Air pollution and carbon emissions are highly homogeneous and closely correlated. The cobenefit and spillover effects of environmental policies have garnered increasing attention in recent years. This study adopts low-carbon city pilot policies as a policy perspective to investigate the comprehensive effect of reducing air pollution and mitigating carbon emissions. By employing the difference-in-differences model, this study examines the impact of low-carbon city pilot policies on air pollution and carbon emissions across 281 Chinese cities, further analyzing the influencing mechanism and heterogeneity of policy effects. The findings of this study indicated that: (1) low-carbon city pilot policies could significantly mitigate urban carbon emissions (−0.117), while increasing air pollution (0.134), thus resulting in the spillover effect. The benchmark regression results passed a series of robustness tests. (2) The spillover effect generated through three influencing mechanisms: market resource crowd-out, industrial structure lock-in, and environmental policy substitution. (3) The local characteristics of cities, such as economic development, resource endowment, and administrative authority, would inevitably influence the implementation of low-carbon city pilot policies. Eastern cities, resource-based cities, and prefecture-level cities have yielded obvious spillover effects. Consequently, this study proposes several policy implications to coordinate urban planning to curb air pollution and carbon emissions, including exploring policy combinations, guiding resource inputs, considering local characteristics, and establishing comprehensive monitoring systems.