Population Exposure to Ambient PM_2.5 at the Subdistrict Level in China

Fine-particulate pollution is a major public health concern in China. Accurate assessment of the population exposed to PM_2.5 requires high-resolution pollution and population information. This paper assesses China's potential population exposure to PM_2.5, maps its spatiotemporal variability, and simulates the effects of the recent air pollution control policy. We relate satellite-based Aerosol Optical Depth (AOD) retrievals to ground-based PM_2.5 observations. We employ block cokriging (BCK) to improve the spatial interpolation of PM_2.5 distribution. We use the subdistrict level population data to estimate and map the potential population exposure to PM_2.5 pollution in China at the subdistrict level, the smallest administrative unit with public demographic information. During 8 April 2013 and 7 April 2014, China's population-weighted annual average PM_2.5 concentration was nearly 7 times the annual average level suggested by the World Health Organization (WHO). About 1322 million people, or 98.6% of the total population, were exposed to PM_2.5 at levels above WHO's daily guideline for longer than half a year. If China can achieve its Action Plan on Prevention and Control of Air Pollution targets by 2017, the population exposed to PM_2.5 above China's daily standard for longer than half a year will be reduced by 85%.