City size expansion in China creates substantial economic circulation, which impacts CO₂ emissions. Since CO₂ production primarily comes from human activities, CO₂ emissions are mainly in cities. To achieve China’s carbon neutrality and provide specific implementation guidance for future carbon-reduction policies, it is worth assessing China’s pressure on carbon reduction in the urban aspect. Highly developed social productivity and a market economy lead to a dramatic increase in the interconnection between cities, and the spatial distribution of CO₂ emissions emerges in a spatial association. Therefore, it is of great significance to investigate the interaction of CO₂ emissions with spatial effects. Taking the Yangtze River Delta urban agglomeration (YRDUA) as the research target area, this paper utilizes city-size indices to construct spatial-association networks of CO₂ emissions for the first time. It employs social network analysis to explore the structures of whole networks, clusters, and city nodes. The main results show that: (1) the spatial associations of CO₂ emissions in the YRDUA’s cities have become tighter over time. (2) The networks of CO₂ emissions in the YRDUA’s cities have noticeable spatial-spillover effects, and the interaction of CO₂ emissions between cities is dominant. (3) Nanjing is the paramount “bridge” node in the networks. (4) Nanjing, Hangzhou, Wuxi, Shanghai, Changzhou, Suzhou, Nantong, and Hefei will be the decisive cities for efficient CO₂ emission control in the future. Overall, this paper reveals the role of carbon reduction in the YRDUA’s cities and proposes suggestions for establishing a transboundary energy-saving mechanism to improve the efficiency of energy conservation and emission reduction.

Business communities in the construction market are becoming increasingly diverse, with a deepening impact on industrial development and enterprise competition. Despite many existing empirical studies on communities, they weaken competitive interactions and have limited applicability to the dynamic issues of community formation and evolution. To address the gaps identified in the literature on bidding competition dynamics, this study constructs a multi-agent system (MAS) model. This model is designed to simulate the formation of community-type rivalry in the construction market by incorporating key variables identified from empirical observations of bidding behavior. It also designs and runs two experiments focusing on the impact of overall market factors and enterprises’ own factors on the formation of an equilibrium state of community-type rivalry to explore the mechanism behind its formation. We find that the density of community networks and the process of community formation are significantly affected by the number of enterprises, the scope of competition among enterprises, and the lifespan of the link, while they are not significantly affected by the size of the market or the exit thresholds of enterprises. In addition, this study finds that, under the bidding competition rule, the number of times that an enterprise bids is closely related to its network location advantage. However, larger and more mature enterprises have difficulty in maintaining a central position in a competitive network. This study provides different perspectives for an understanding of corporate community formation and offers valuable insights into the governance of community phenomena in the construction market.