Particulate pollution is currently regarded as a severe environmental problem, which is intimately linked to reductions in air quality and human health, as well as global climate change. Accurately identifying the key factors that drive air pollution is of great significance. The temporal and spatial heterogeneity of such factors is seldom taken into account in the existing literature. In this study, we adopted a geographically and temporally weighted regression model (GTWR) to explore the direction and strength of the influences of natural conditions and socioeconomic issues on the occurrence of PM2.5 pollutions in 287 Chinese cities covering the period 1998 to 2015. Cities with serious PM2.5 pollution were discovered to mainly be situated in northern China, whilst cities with less pollution were shown to be located in southern China. Higher temperature and wind speed were found to be able to alleviate air pollution in the country's southeast, where enhanced precipitation was also shown to reduce PM2.5 concentrations; whilst in southern and central and western regions, precipitation and PM2.5 concentrations were positively correlated. Increased relative humidity was found to reinforce PM2.5 concentration in southwest and northeast China. Furthermore, per capita GDP and population density were shown to intensify PM2.5 concentrations in northwest China, inversely, they imposed a substantial adverse effect on PM2.5 concentration levels in other areas. The amount of urban built-up area was more positively associated with PM2.5 concentration levels in southeastern cities than in other cities in China. PM2.5 concentrations conformed to a series of stages and demonstrated distinct spatial differences in China. The associations between PM2.5 concentration levels and their determinants exhibit obvious spatial heterogeneity. The findings of this paper provide detailed support for regions to formulate targeted emission mitigation policies.

Increasing Chinese urbanization and industrialization has prompted greater attention to the study of human settlement and the human-land relationship in the fields of geography, architecture, and urban planning. We used bibliometric methods and statistical software to review 180 articles on human settlement in 16 Chinese geographical journals. We found that Chinese geographical human settlement research is characterized by the following: (1) Most research focuses on human settlement extension, valuation indicators, models for urban and rural settlements, theoretical exploration and the planning practices of single-factor, human settlement and complex, geographical livability in macro-scale, urban settlement differentiation and ideal patterns in medium scale, the comprehensive evaluation of settlement environment, and the planning of community units in micro-scale, community settlements; socio-cultural investigation and warnings about advancing human settlement. (2) No progress has been made in synthesizing and integrating method systems. PSR models and DPSIR models are used for targeting mechanisms, while the standard settlement evaluation system was composed of physical & economic indicators by questionnaire surveys. On the other hand, spatial clustering based on GIS has been a frequent focus in recent years. Pioneering research on human settlement and theoretical systems within the context of China’s urbanization and industrialization will provide guidance on the sustainability of Chinese cities and regions. The following five aspects require greater attention: (1) Natural suitability research on human settlement, and a survey of human settlement demands to reflect the range of different demands concerning ecologically suitable settlements in urban environments, the corresponding valuation indicators, systems, and evolution, and the impact of the residents’ socio-economic attributes. (2) Spatial-temporal evaluation and sustainability research on urban and rural human settlement at various scales, focusing on evolution and spatial differentiation at various scales such as city clusters and comparisons between cities, within the cities and communities. (3) Development of theory and technology for human settlement evolution research, including detection technology and methods, data mining measures, and forecasting and emulation of regional and urban human settlement evolution processes, mechanisms and patterns. (4) Research on the control of human settlement that focuses on optimization, patterns, and policies for effective management and development. (5) Estimating the human settlement system service value and establishing suitable human settlement systems, including social, economic, cultural and ecological service values.