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

Highlights: • PM_2.5 increased in most areas of South-Southeast Asia from 1999 to 2014. • Bangladesh and Pakistan had higher PM_2.5 than other countries in South-Southeast Asia. • South-Southeast Asia had an increased rate of 0.02 μg/m³/year from 1999 to 2014. • The population proportion exposed to high PM_2.5 (> 35 μg/m³) increased notably. • Areas with high health risk expanded in size and extent between 1999 and 2014. Fine particulate matter, or PM_2.5, is a serious air pollutant and has significant effects on human health, including premature death. Based on a long-term series of satellite-retrieved PM_2.5 concentrations, this study analyzed the spatial and temporal characteristics of PM_2.5 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 PM_2.5 between 1999 and 2014 was then undertaken. The results show that PM_2.5 concentrations increased in most areas of SSEA from 1999 to 2014 and exceeded the World Health Organization average annual limit of primary PM_2.5 standards. Bangladesh, Pakistan and India experienced average PM_2.5 values higher than the total average for SSEA. From 1999 to 2014, the entirety of SSEA exhibited an increased rate of 0.02 μg/m³/year on average. Bangladesh and Myanmar witnessed greater incremental rates of PM_2.5 than India. Correspondingly, the center of the average regional PM_2.5 concentration gradually shifted to the southeast during the study period. The proportion of areas with PM_2.5 concentrations exceeding 35 μg/m³ increased consistently, and the areas with PM_2.5 concentrations below 15 μg/m³ decreased continuously. The proportion of the population exposed to high PM_2.5 (above 35 μg/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 PM_2.5 concentrations in SSEA countries are urgently required.