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

ABSTRACT

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.