City as a major source area of fine particulate (PM2.5) in China.

The PM2.5 concentration in 31% of China's territorial areas was less than 10 μg/m(3), and in 26% of China's territorial areas was higher than 35 μg/m(3). High concentrations of PM2.5 were found in the East China Plain, Sichuan province, and the Taklimakan desert. East China Plain was also found with strong significant positive trends. 73% of artificial surface (L01) was found with significant positive trends, but only 2% with significant negative trends. 76% of cropland (L02) was observed with significant positive trends, but only 2% with significant negative trends. The mean significant trends of PM2.5 concentration were 1.81 μg/m(3)·year for L01 and 1.71 μg/m(3)·year for L02, higher than that for the rest land covers. The PM2.5 pollution brought potential health risk to susceptible population: only 1% of thm lives at a safe level (<10 μg/m(3)), but 69% of them were exposed to heavy PM2.5 pollution (>35 μg/m(3)).