Variability in Transport Pathways and Source Areas of PM10 in Beijing during 2009-2012

The transport pathways and source areas of PM10 in Beijing were examined on the basis of a model-assisted analysis. Computed back trajectories were used to trace the air history. The aim of this work was to study the main source areas of PM10, the variability of transport pathways, and potential source areas in Beijing. The results reveal that the major potential source areas of PM10 in Beijing were Hebei, Shandong, Tianjin, northwest of Inner Mongolia, and Outer Mongolia. The main source areas of PM10 have changed from the northwest to the south and southeast of Beijing during 2009–2012. During the study period, the regional contributions of PM10 from Shandong, Tianjin and Henan increased, whereas those from Inner Mongolia and Mongolia decreased compared with 2003–2009. The northwest airflow is a key factor in extreme pollution episodes. Sand storm partly contributed to the PM10 concentration in fast northwesterly transport paths. PM10 concentrations in winter and spring were higher than autumn and summer. In spring and summer, Beijing was strongly affected by long-range transport. Long-range transport had a weaker effect on PM10 concentrations during autumn and winter. The clustering of back-trajectories and PSCF results indicate the need to reduce PM10 transport from areas surrounding Beijing, particularly from the south of Beijing.