A new approach to evaluate regional inequity determined by PM_2.5 emissions and concentrations

PM_2.5 is one of the most severe types of air pollution that threatens human health. Its emissions have a notable spillover effect once released into the atmosphere and transported. In domestic trade, PM_2.5 emissions can be indirectly imported from external regions. Thus, regional inequity caused by PM_2.5 needs to be integrated and comprehensively estimated. Based on PM_2.5 emissions/concentrations grid maps and an input-output model, this study first examined the temporal-spatial changes in PM_2.5 emissions/concentrations across China. Additionally, a detailed relationship between PM_2.5 emissions and concentrations was examined at multiple scales, both temporal and spatial. Finally, this study developed a new approach with which to evaluate regional inequity. The results show that PM_2.5 emissions and concentrations increased between 1990 and 2012 and 1998 and 2016, respectively; the increase was more obvious for PM_2.5 emissions. Spatially, a rapid increase in PM_2.5 emissions was observed in the North China Plain and the Sichuan Basin. Between 1998 and 2012, the distribution of PM_2.5 concentrations was similar to that of emissions; however, between 2013 and 2016, 46.6% of the total area showed a decrease, mainly in the central and southern parts of China. Relationship analysis revealed that PM_2.5 emissions and concentrations are closely correlated in both time and space. There was obvious regional inequity among provinces; developed regions always imported considerably more PM_2.5 emissions from undeveloped regions than they exported. Overall, the regional inequity estimation framework shows that provinces along the coastline, especially developed provinces, have advantages under the regional inequity estimation framework, while most of the inland regions have disadvantages, especially in the west and north.