Study on the impact of urban underground public space expansion on near-ground carbon monoxide concentrations

As global urbanization intensifies and land resource constraints become increasingly severe, the development of underground public space (UPS) has emerged as a crucial strategy for optimizing urban spatial structures and enhancing carrying capacity. However, the impact of the mechanism on near-ground carbon monoxide (CO) concentrations remains unclear, and most relevant studies lack a systematic quantitative assessment. Therefore, this study designs an analysis framework to examine the impact of urban UPS on near-ground CO concentrations based on multi-year large-scale Point of Interest (POI) data. Then taking Shanghai, Chengdu, and Jinan in China as case studies, spatial partition statistics and a panel fixed-effects model are conducted to explore the impact of urban UPS expansion on near-ground CO concentrations and the urban heterogeneity with data from 2015, 2017, 2020, and 2022. The results demonstrate that the UPS development has a positive effect in reducing CO concentrations. In particular, the panel fixed-effects model reveals a significant negative correlation between the number of in Underground Point of Interest (UPOI) and CO concentration levels. However, significant differences exist among cities: Shanghai and Chengdu show a steady decline in CO concentrations as the unit POI increases, with a more significant emission reduction effect in high-growth zones. Jinan has the strongest marginal emission reduction per unit POI, but the overall decrease in CO concentrations in its high-growth zones is the smallest due to topographical constraints, industrial structure, and the current stage of UPS development. This study reveals the net environmental benefits of UPS development from the city system scale, enhances the understanding of the complex environmental relationship between underground and ground, and provides a scientific basis for differentiated underground space planning and air pollution control in different cities.