| A total of 54 atmospheric precipitation samples were collected from 42 precipitation events in Qingdao from June 2020 to June 2021. The concentration, solubility, sources, and influencing factors of eight metal elements, including Al, Fe, Zn, Cu, Pb, Ni, Cd, and V, were analyzed. Al, Fe, and V were mainly from natural sources, and the other metals were affected by the comprehensive effect of natural and anthropogenic sources. All the metal concentrations varied greatly. Al and Fe were the major elements, with average concentrations of (710.9±969.4) μg·L-1 and (409.1±503) μg·L-1, respectively. The other trace elements, Zn, Ni, Cu, Pb, V, and Cd, had concentrations of (71.7±37.9) μg·L-1, (8.9±14.4) μg·L-1, (7.5±8.5) μg·L-1, (1.8±2.3) μg·L-1, (1.6±1.6) μg·L-1, and (0.1±0.1) μg·L-1, respectively. The solubility of trace elements was generally higher than that of major elements. Ni, Cu, Zn, and Pb had solubilities of (44.8±28.2)%, (36.2±28.3)%, (34±28.6)%, and (14.1±11.8)%, respectively. The solubilities of Al and Fe were as low as (6.5±11.8)% and (6.1±15.8)%, respectively. During the continuous precipitation process, the concentration and solubility variation of trace metals were more complex than those of Al and Fe, which had high background values in the atmosphere. From the onset to the middle period of precipitation, the average concentration of Al and Fe changed little, and the proportion of Al and Fe to the sum concentration of these eight elements increased by 1%-3%, whereas the concentration of trace elements decreased obviously; for example, the concentration of Cu and Cd decreased by approximately 80%. When the rainfall exceeded 20 mm, the concentrations of Al and Fe decreased rapidly by approximately one-third compared to those at the initial stage. At this time, the removal rate of trace metals, such as Zn, Cu, and Pb, was basically saturated. The removal rate of the sum concentration of these eight elements was 20%-60%. Except for Al, the solubility of all elements increased at the early stage and then decreased with the increase in rainfall, which was related to precipitation frequency, rainfall, and metal source. The metals in Qingdao precipitation were mainly from secondary aerosols and biomass combustion (37.28%), sea salt aerosols (29.21%), dust (17.91%), the shipping and petroleum industry (8.36%), and automobile exhaust emissions and other activities (7.24%). |
