Globally analysing spatiotemporal trends of anthropogenic PM concentration and population's PM exposure from 1998 to 2016.

Air pollution in the form of particulate matter (PM) is becoming one of the greatest current threats to human health on a global scale. This paper firstly presents a Bayesian space-time hierarch piecewise regression model (BSTHPRM) which can self-adaptively detect the transitions of local trends, accounting for spatial correlations. The spatiotemporal trends of the approximately anthropogenic PM removed natural dust (PM) concentrations and the corresponding population's PM exposure (PPME) in the global continent from 1998 to 2016 were investigated by the presented BSTHPRM. The total areas of the high and higher PM-polluted regions, whose spatial relative magnitude of PM pollution to the global continental overall level was between 1.89 and 14.68, accounted for about 13.4% of the global land area, and the corresponding exposed populations accounted for 56.0% of the global total population. The spatial heterogeneity of the global PM pollution increased generally from 1998 to 2016. The areas of hot, warm, and cold spots with increasing trends of PM concentration initially contracted and then later expanded. The local trends of the global continental PM concentrations and PPME can be parted into three changing stages, early, medium, and later stages, using the BSTHPRM. The area proportions of the regions experiencing a decreasing trend of PM concentrations and PPME were greater in the medium stage than in the early and later stages. The local trends of PM concentration and PPME in the two higher PM polluted areas, northern India and eastern and southern China, increased in the early stage and then decreased in the medium stage. In the later stage (recent years), northern India displayed a stronger increasing trend; nevertheless, the follow-up decreasing trend still occurred in eastern and southern China. In the first two stages, more than half of the areas in Europe experienced a decreasing trend of PM concentration and PPME; later, more than half of areas in Europe exhibited increasing trends in the later stage. North America and South America experienced a similar local trend of PPME to Europe. The PPME trend in Africa generally increased during the study period.