Synergies of air pollution control policies: A review

Air pollution control necessitates the implementation of multiple policy instruments in a coordinated manner. However, the enforcement of different policy combinations may generate complementary or offsetting synergistic effects, thereby influencing policy effectiveness. Nevertheless, the direction of synergy and the mechanisms of action among heterogeneous policies is undefined in existing academic research. This study systematically reviewed 773 articles from 1998 to 2023 and, for the first time, integrated four primary domains of air pollution control policies: policy synergy and integration, collaborative governance for pollution and carbon mitigation, joint control of multiple pollutants, and cross-regional cooperative governance. This study revealed the directions and mechanisms of air policy synergy and provided empirical evidence for cross-regional comparisons in global environmental governance, with the ultimate goal of enhancing the effectiveness of air pollution control policies. Specifically, the mechanisms underlying policy synergy suggest that the cumulative impact of policies leads to the synergistic effects of multiple policies being superior to the effects of implementing a single policy. Furthermore, due to market price signals or the characteristics of specific technologies, the concurrent application of multiple policies may occasionally yield negative synergistic outcomes. Despite these advancements, gaps remain particularly in broadening the scope of policy integration, refining the assessment of synergistic effects, developing control strategies, and enhancing stakeholder engagement. Further research is necessary to address these gaps and enhance air policy effectiveness.