Population and industry are closely related to CO₂ emissions in Cities. However, few studies have explored the joint influence of population size and industrial structure on CO₂ emissions. This paper examined the nonlinear influence of population size and industrial structure on CO₂ emissions by using a threshold-STIRPAT model with the latest available data in 2001–2017 from 255 cities in China. Results indicated that the promotion effect of urban population size on CO₂ emissions increased in the first two stages and then decreased in the third stage when the industrial structure exceeded the threshold value of 1.22. Meanwhile, the industrial structure had a positive impact on CO₂ emissions if the urban population was less than 1.38 million. However, the previous promotional effect became an inhibitory effect when the urban population exceeded 1.38 million. According to the above findings, it is necessary to find a reasonable match between urban population size and industrial structure. Specifically, China should formulate differentiated urban population policies in cities with different industrial structures. In addition, for cities with a population size of more than 1.38 million, adjusting the industrial structure to give priority to the tertiary industry will be an effective way to reduce CO₂ emissions.

Economic development highly depends on resources and the environment, especially in the Yellow River Basin (YRB), a crucial ecological protection and high-quality development pilot zone in China. Thus, evaluating high-quality economic development (HQED) and its decoupling relationship with the resource environment is conducive to planning future regional development. First, this paper used the two-stage entropy method to measure the high-quality economic development of cities in the YRB from 2010 to 2019. Then, the comprehensive decoupling analysis of the resource environment and high-quality economic development was carried out based on the Tapio decoupling model. The results showed that: (1) The high-quality economic development level improved slowly in the YRB. Nevertheless, the resource and environmental pressure gradually decreased. (2) Compared with the resource decoupling index, the environmental decoupling index had a greater impact on the comprehensive decoupling index in the YRB. The strong decoupling displayed a spatial diffusion trend from point to surface. (3) Despite the decoupling types having a positive transfer trend in the YRB, the decoupling states of cities fluctuated considerably, and the phenomenon of recoupling occurred frequently. According to the above findings, this study put forward some policy recommendations for achieving strong decoupling in the YRB.

Due to the fast growth of China’s economy, urban atmospheric pollution has become a serious problem affecting the public’s physical and mental health. The ‘2 + 26’ cities, as the Jing-Jin-Ji atmospheric pollution transmission channel, has attracted widespread concern. There were several previous studies on the economic loss of public health caused by PM_2.5 pollution in ‘2 + 26’ cities. To assess the economic loss caused by PM_2.5 on human health in ‘2 + 26’ cities, this paper used the exposure-response model, the health effect loss model and willingness to pay method to obtain the economic loss from PM_2.5 pollution with the latest available data in 2020. It was concluded that, in 2020, the economic loss of ‘2 + 26’ cities from PM_2.5 was spatially distributed low in the east and high in the west. In addition, it was larger in the southern and northern part, which was smaller in the middle of the region. Based on the conclusions, policy recommendations were put forward.

Water resource scarcity is a major obstacle to the sustainable development of the Yellow River Basin (YRB). Accurately identifying the decoupling pathways of water resources ecological footprint (WEF) and economic growth is crucial in resolving the dilemma of water resource utilization and economic development in the YRB. To explore the decoupling states of WEF and the economic growth in cities within the YRB, this study proposed a new two-dimensional decoupling model with 24 different decoupling states, based on the Tapio decoupling model and the environmental Kuznets curve (EKC) hypothesis. Using the panel data from 60 cities in the YRB from 2010–2021, this study found that the relationship between WEF and per capita GDP followed an N-shape pattern. Decoupling performance shows clear regional differentiation: downstream cities exhibited the best decoupling performance, followed by the midstream cities, while the upstream cities showed the poorest performance. The change trajectory of decoupling states showed a clear tendency toward desirable decoupling: the proportion of cities achieving high-economic-level decoupling states (HE-SD and HE-WD) increased markedly from 18.33% to 43.33%. However, this transition was highly dynamic and non-linear, nearly 95% of cities experienced changes in their decoupling states during the study period. These results highlight the urgency of decoupling water resource utilization from economic growth throughout the YRB. In light of the aforementioned discoveries, this paper proposed corresponding policy recommendations aimed at achieving the ideal decoupling of WEF and economic growth in the Yellow River Basin.