Long-term trends and spatial patterns of satellite-retrieved PM2.5 concentrations in South and Southeast Asia from 1999 to 2014.

Fine particulate matter, or PM2.5, is a serious air pollutant and has significant effects on human health, including premature death. Based on a long-term series of satellite-retrieved PM2.5 concentrations, this study analyzed the spatial and temporal characteristics of PM2.5 in South and Southeast Asia (SSEA) from 1999 to 2014 using standard deviation ellipse and trend analyses. A health risk assessment of human exposure to PM2.5 between 1999 and 2014 was then undertaken. The results show that PM2.5 concentrations increased in most areas of SSEA from 1999 to 2014 and exceeded the World Health Organization average annual limit of primary PM2.5 standards. Bangladesh, Pakistan and India experienced average PM2.5 values higher than the total average for SSEA. From 1999 to 2014, the entirety of SSEA exhibited an increased rate of 0.02μg/m3/year on average. Bangladesh and Myanmar witnessed greater incremental rates of PM2.5 than India. Correspondingly, the center of the average regional PM2.5 concentration gradually shifted to the southeast during the study period. The proportion of areas with PM2.5 concentrations exceeding 35μg/m3 increased consistently, and the areas with PM2.5 concentrations below 15μg/m3 decreased continuously. The proportion of the population exposed to high PM2.5 (above 35μg/m3) increased annually. The extent of high-health-risk areas in SSEA expanded in size and extent between 1999 and 2014, particularly in North India, Bangladesh and East Pakistan. Therefore, all of SSEA should receive special attention, and strict controls on PM2.5 concentrations in SSEA countries are urgently required.