Spatiotemporal patterns of remotely sensed PM2.5 concentration in China from 1999 to 2011

Air pollution in the form of fine particulate matter, or PM2.5, can decrease human life expectancy and increase the overall mortality rate. Based on a time series of remotely sensed PM2.5 concentrations, this study analyzed the spatiotemporal patterns of this crucial pollutant in China from 1999 to 2011 using trend analysis and standard deviation ellipse analysis, and carried out a health risk assessment of human exposure to PM2.5. The results showed that PM2.5 concentrations increased significantly from 1999 to 2011 in China, especially in the central and eastern parts of the country. The proportion of areas with PM2.5 concentrations higher than 35 μg/m3 increased year by year, and the areas with PM2.5 concentrations lower than the annual primary standard of 15 μg/m3 decreased continuously. The areas most polluted by PM2.5 were south of Hebei, north of Henan and west of Shandong provinces, with changes in the overall spatial distribution of the pollutant occurring faster along a south-north axis than along an east-west axis, and also faster along an east-south axis than along a west-north axis. Based on the PM2.5 concentrations in China from 1999 to 2011, a two-tier standard (level-I and level-II) was proposed for delineated areas to assist in nationwide air pollution control. It was also found that the proportion of the population exposed to PM2.5 concentrations greater than 35 μg/m3 increased year by year, and increased faster than the proportion of population exposed to PM2.5 concentrations in the range 15-35 μg/m3. The health risk in the central and eastern areas of the country was the highest. Based on these results, PM2.5 pollution poses an increasingly serious risk to human health across China and there is an immediate need to implement its regional control. In addition, more attention should be paid at the national scale in terms of pollution risk, rather than focusing narrowly on a city scale.