[Concurrent Measurement of Wet and Bulk Deposition of Trace Metals in Urban Beijing]

To characterize the dry and wet deposition of atmospheric trace elements in urban Beijing, both active and passive samplers were used to collect bulk and wet sedimentation samples between May 2014 and April 2015.The concentrations of 19 trace elements (Na, Mg, Al, K, Ca, V, Cr, Mn, Fe, Cu, Zn, As, Se, Mo, Cd, Sb, Tl, Th, and U) in the samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The results show that the concentrations of metals in bulk deposition samples[7160.68 μg·L^-1 (Ca)-0.02 μg·L^-1 (Th)] were generally higher than those in wet deposition samples[4237.74 μg·L^-1 (Ca)-0.01 μg·L^-1 (Th)], but the enrichment factors of each metal in the two kinds of samples were less different. Of note, the enrichment factors of Cu, As, Tl, Zn, Cd, Se, and Sb were all larger than 100, thus indicating that these heavy metals were mainly from anthropogenic sources. The statistical analysis of the air mass trajectory shows that the precipitation chemistry in urban Beijing is mainly affected by southward air flows. The air mass originating from the southwest region always had higher concentrations of Ca, Mg, Fe, Al, Cu, Mo, U, and Th, whereas the air mass from the south had higher concentrations of K, Zn, Mn, Sb, Cd, and Tl. During the observation period, the bulk deposition fluxes of metals varied from 3591.35 mg·(m²·a)^-1 (Ca)-0.01 mg·(m²·a)^-1 (Th), and wet deposition fluxes varied from 1847.78 mg·(m²·a)^-1 (Ca)-0.01 mg·(m²·a)^-1 (Th). The dry deposition fluxes of the 19 metals varied from 1743.57 mg·(m²·a)^-1 (Ca)-0.01 mg·(m²·a)^-1 (Th). The particle size has important implications in the evaluation of the relative importance of dry deposition versus wet deposition during the scavenging of trace elements in air.