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The chemical composition of aerosols in regional background areas is important for understanding the impacts of anthropogenic emissions on atmosphere.This paper presents an intensive field measurement campaign carried out continuously at the rural mountainous site of Xinglong (960 m a.s.l.) in Northern China during Sep.3-20 2008.Size-segregated samples were collected daily and analyzed for 25 trace elements (TEs).The majority of the TEs showed comparable concentrations in fine (< 2.1 μm) and coarse particles (2.1-9 μm).In addition,elements like K,Mn,Cu,Se,Mo,Ag,Cd,Tl and Pb were accumulated in fine mode whereas Al,Co and Sb were concentrated in coarse mode.For most of the TEs,their enrichment factor (EF) values increased with decreasing particle size from large (> 9 μm) to coarse,and to fine,signifying influences by anthropogenic emissions.The observed concentrations of heavy metals in fine particles,with EF values higher than 100,were significantly higher than the historical data recorded in the 1980s and 1990s,reflecting the increasing emissions in the target area.One pronounced event occurred on Sep.14 when all of the TEs showed a peak,which was associated with regional emissions from both southeast (SE) and southwest (SW) indicated by backward trajectory analysis.This is further supported by the measurements in upwind sites where the concentrations of TEs were several times higher than those in Xinglong,suggesting potential source regions.Episodes of heavy metals were generally characterized by significant enhancements of fine mode and air mass trajectories from SE or SW alone.Taking this finding and factor analysis results together,the metallic episodes were attributable to the long-range transport of regional plumes from coal consumption and nonferrous metals smelting.With the rapid urbanization and industrialization in Northern China,the increasing emissions of TEs will place a great strain on human health and the environment in the downwind regions,thus long-term and multi-site observation with high time resolution are necessary.