Long-range transport and regional sources of PM2.5 in Beijing based on long-term observations from 2005 to 2010

Haze pollution in Beijing is rather deteriorated. Long-term measurement of PM2.5 from 2005 to 2010 at an urban site in Beijing showed very high concentration level with an annual average 74 ± 55 μg/m3. The contribution of regional sources is one of the most important factors; thus, transport and regional sources of PM2.5 in Beijing are investigated using the trajectory cluster and receptor models (potential source contribution function and trajectory sector analysis). The results indicated that the highest concentrations of PM2.5 (76–120 μg/m3) were associated with south, southeast, and short northwest trajectories, and moderate concentrations (46–67 μg/m3) with long northwest and short north trajectories, and the lowest concentrations (20–33 μg/m3) with long north trajectories. During the relatively polluted periods, the probable locations of regional emission sources were mainly in the south and the west of Beijing and varied according to different seasons. Between 2005 and 2010, the annual mean contribution of 35.5% (32.8 μg/m3) for PM2.5 was attributed to long-distance transportation. The transported contribution percentages from 2005 to 2010 for PM2.5 showed an increasing tendency with a linear rate of 1.2/year.