Urban clusters are the main trend of current and future urbanization worldwide, but their impact on environmental pollution has been controversial. This paper explores this issue in the context of urban development in China, and analyzes the underlying mechanisms, using panel data from 285 Chinese cities spanning 2006 to 2021. The findings show that a one unit increase in the degree of urban cluster is associated with a reduction in the comprehensive pollution index by approximately 7.5%, and the main mechanisms by which urban clusters facilitate environmental protection are congestion alleviation, industry structural optimization, and technological innovation. Firstly, urban clusters reduce environmental pollution by mitigating the crowding effects associated with urban expansion, although this alleviation is predominantly observed in larger cities. Secondly, urban clusters foster the upgrading of urban industrial structures, thereby decreasing environmental pollution. However, in less developed cities where industrialization is a major development goal, the impact of structural optimization is less pronounced. Finally, technological innovations, including advances in technologies of energy conservation and emission reduction, have assisted in the transformation of the economic growth model, which has reduced environmental pollution. Looking ahead, the urban cluster remains a pivotal strategic direction for social development, and planning and construction of urban clusters should actively incorporate environmental benefit considerations.

This study adopts a systems perspective to examine the persistent effects of China’s One-Child Policy (OCP) on the subjective well-being of older adults, emphasizing structural persistence, reinforcing feedback, and path-dependent lock-in in complex socio-technical systems. Using nationally representative data from the China Longitudinal Aging Social Survey (CLASS-2014), we exploit the OCP’s formal rollout at the end of 1979—operationalized with a 1980 cutoff—as a quasi-natural experiment. A Fuzzy Regression Discontinuity (FRD) design identifies the Local Average Treatment Effect of being an only-child parent on late-life well-being, mitigating endogeneity from selection and omitted variables. Theoretically, we integrate three lenses—policy durability and lock-in, intergenerational support, and life course dynamics—to construct a cross-level transmission framework: macro-institutional environments shape substitution capacity and constraint sets; meso-level family restructuring reconfigures support network topology and intergenerational resource flows; micro-level life-course processes accumulate policy-induced adaptations through education, savings, occupation, and residence choices, with effects materializing in old age. Empirically, we find that the OCP significantly reduces subjective well-being among the first generation of affected parents decades later (2SLS estimate ≈ −0.23 on a 1–5 scale). The effects are heterogeneous: rural residents experience large negative impacts, urban effects are muted; men are more adversely affected than women; and individuals without spouses exhibit greater declines than those with spouses. Design validity is supported by a discontinuous shift in fertility at the threshold, smooth density and covariate balance around the cutoff, bandwidth insensitivity, “donut” RD robustness, and a placebo test among ethnic minorities exempt from strict enforcement. These results demonstrate how demographic policies generate lasting impacts on elderly well-being through transforming intergenerational support systems. Policy implications include strengthening rural pension and healthcare systems, expanding community-based eldercare services for spouseless elderly, and developing complementary support programs.