Considering the sensitivity to environmental safety is rooted in human genes, the external variables that affect the perception of environmental safety and their influence mechanisms have become a point of concern. The existing literature has proven that elements of the built environment are vital influencing factors; however, little is known about the mechanism by which the built environment affects perceived safety and multiple influence pathways have been ignored. Based on defining the concept of perceived safety, this article applies a structural equation model to study the relationship between the built environment and residents’ safety perception with the social environment and physical activity as potential mediators. The statistical results suggest that the variables of the built environment, social factors, and physical activity all significantly influence perceived safety. This finding also reveals that the social environment and group physical activities slightly mediate the relationship, proving that the built environment exerts both direct and indirect effects on perceived safety. This study provides evidence that built environment design is more important than previously thought because it contributes positively to the social atmosphere and encourages the passion for physical activities, which are also beneficial to safety perception.

The research on the correlation between pollutant dispersion and wind environment is gaining more and more attention due to increasingly serious air pollution. However, the specific relationship between wind environment factors and the pollutant concentration is still unclear. In this paper, a simple model of the relationship among wind speed, pollutant concentration, and pollutant dispersion efficiency is investigated based on computational fluid dynamics (CFD) simulations to redefine the static wind speed on the aspect of pollutant dispersion. The air pollutants are supposed to be diffused effectively when the wind speed is higher than the static wind speed. The CFD simulations are performed using the three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) methods. First, the numerical methods and CFD settings are described briefly and then validated by experimental data. Next, an idealized pollutant dispersion model is established and then the pollutant dispersion processes are simulated and analyzed with different wind speed profiles. Finally, wind with speed less than 1.0 m/s at pedestrian level (1.5 m above the ground) is defined as static wind according to the comparison and analysis. It is expected that the static wind speed results can be easily used as an indicator to evaluate air quality directly for urban design and planning.

In response to the core issue of how urban land planning can promote the level of sustainability, this paper takes the perspective of urban land change and draws on the requirements of the metabolic model in sociology. It takes the indicators of urban land planning and allocation as the core of regulation and constructs a theoretical model for urban sustainability planning in three dimensions: urban social, economic, and ecological environment. In the urban life support system, nine resource subsystems including land, water, atmosphere, population, transportation, energy, cultural tourism, basic supporting facilities, and public service facilities are constructed. At the same time, an empirical technical concept composed of a interdisciplinary quantitative model group is provided, aiming to provide ideas for the theoretical and empirical technology of urban sustainability planning.