Main Chemical Components in Atmospheric Precipitation and Their Sources in Xi'an

Abstract

In order to understand the current status of main chemical components of atmospheric precipitation in Xi'an, the pH, electrical conductivity, mass concentration of water-soluble ions and heavy metals, wet deposition fluxes, and their sources in precipitation samples in urban and suburban areas of Xi'an in 2019 were studied. The results showed that the pH, conductivity, water-soluble ions, and heavy metals in precipitation in Xi'an in winter were higher than those in other seasons. The main water-soluble ions in precipitation were Ca2+, NH+4, SO2-4, and NO-3, and the sum of these ions accounted for (88.5%±2.8)% of the total ion concentration in urban and suburban areas. The main heavy metals were Zn, Fe, and Zn and Mn; their sum accounted for (54.0%±3)% and (47.0%±8)% of the total metal concentration. The wet deposition fluxes of water-soluble ions in precipitation in urban and suburban areas were (253.2±58.4) mg·(m2·month)-1 and (241.9±61.1) mg·(m2·month)-1, respectively. They showed higher values in winter than those in other seasons. The wet deposition fluxes of heavy metals were (86.2±37.5) mg·(m2·month)-1 and (88.1±37.4) mg·(m2·month)-1, respectively, with little seasonal difference. The source analysis using PMF showed that the water-soluble ions in urban and suburban precipitation mainly came from combustion sources (57.5% and 32.32%), followed by motor vehicles (24.4% and 17.2%) and dust sources (18.1% and 27.0%). The ions in suburban precipitation were also affected by local agriculture (11.1%). Heavy metals in precipitation in urban and suburban areas mainly came from industrial sources (51.8% and 46.7%), and the contribution rate of coal and motor vehicle mixed sources in winter was 10.7% and 6.1% higher than that in summer, respectively.