*6.3. Limitations and Future Research Possibilities*

However, this paper also has some limitations: on the one hand, the research sample of this paper is the data from the city level in China. In the future, when carbon emissions data at the corporate level becomes available, we can investigate the carbon effect of the city cluster policy from a micro-enterprise perspective. On the other hand, although this paper explores the carbon reduction effect of the city cluster policy, it does not examine its impact on human health. In the future, we will merge relevant micro-survey data to study the impact of city cluster policy on individual health.

**Author Contributions:** Conceptualization, X.L.; Data curation, C.H., S.Z. and Y.W.; Formal analysis, C.H.; Investigation, S.Z.; Methodology, X.L.; Project administration, X.L.; Supervision, Y.W.; Validation, S.Z.; Visualization, Y.W.; Writing—review & editing, C.H. and S.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
