Temporal patterns and socioeconomic controls of PM2.5 across global cities

As PM_2.5 pollution poses increasing challenges to human health and sustainable development, further understanding its temporal patterns is significant to develop targeting and effective strategies for pollution control. However, the temporal patterns of PM_2.5 for each city worldwide over the past two decades, their controlling factors and difference between urban and rural areas need to be further investigated. Therefore, this paper proposes to identify temporal patterns of PM_2.5 from 2000 to 2020 and further explores the related factors for these temporal patterns. There are two major findings summarizing as follows. (1) The global temporal patterns of PM_2.5 are grouped into four typical types based on the decision tree classification with Savitzky-Golay filtering and Mann-Kendall trend test, verified through visual interpretation on a case-by-case basis. The four typical patterns are Gradual-Decreasing Type (GDT), Single-Peak Type (SPT), Single-Valley Type (SVT) and Gradual-Increasing Type (GIT), accounting for 16%, 49%, 2% and 16%, respectively. The rest of global cities exhibit none of the features in temporal patterns of PM_2.5 (17%). The urban and rural areas show similar temporal patterns in the global PM_2.5 pollution. (2) The temporal patterns of PM_2.5 in cities around the world are greatly influenced by the level of economic development. The GDT predominates in very high human development cities, comprising 55% of the global cities. In contrast, SPT and GIT account for 71% and 23% of medium human development cities, where pollution concentrations peaked or increases with economic growth. Additionally, nature-based factors for temporal patterns, PM_2.5 urban pollution island, strategy proposal and research prospects are discussed. This paper aims to better understand the sources, dispersion, and accumulation processes of pollutants, and provide scientific basis for governments and environmental protection agencies to help propose more effective pollution prevention and control measures.