Composition characteristics and source apportionment of water-soluble ions in atmospheric wet precipitation of Jiaozhou Bay

The composition, sources and wet deposition fluxes of major water-soluble ions [Na+、K+、Ca2+、Mg2+、NH4+、F-、Cl-、SO42-、NO3-、MAS- (methylsulfonate)] in precipitation were analyzed based on the atmospheric precipitation samples along the coast of Jiaozhou Bay from June 2019 to August 2020. The contribution of water-soluble ions to nutrients and potential ecological effects on coastal ecosystem were evaluated, and their main sources were analyzed using the air mass backward trajectory and Positive Matrix Factorization (PMF) model. Volume-weighted Mean (VWM) pH of precipitation over Jiaozhou Bay is 6.41, and the VWM value of electrical conductivity is 19.3µS/cm. The water-soluble ions in precipitation are mainly Na+、NH4+、NO3-、Cl- and SO42- and their concentrations in winter and spring are significantly higher than those in summer and autumn, while the wet deposition flux is mainly concentrated in summer (about 55%) due to the control of precipitation. During the study period, the atmospheric precipitation removed 7274.6t of water-soluble ions from atmosphere and about 951.9t/a of nutrients (mainly NH4+ and NO3-, in terms of nitrogen) were deposited into Jiaozhou Bay, indicating that the atmospheric precipitation exacerbated marine environment pollution and led to the imbalance of marine ecosystem in the process of cleaning the atmosphere. Four types of air masses controlling the precipitation over Jiaozhou Bay were obtained from the analysis of the air mass backward trajectory. In different seasons, the precipitation process was affected by different air masses, among which the air masses from East China and northeast direction had a greater influence. The source analysis results based on PMF showed that the water-soluble ions in the atmospheric precipitation in Jiaozhou Bay were jointly controlled by agricultural sources, marine sources, dust sources, biomass and refuse combustion sources, industrial and traffic sources. The contribution of agricultural sources was the most prominent (26.7%), while the contribution of other four sources is roughly equal. The study proves that the atmospheric environment of Jiaozhou Bay is constrained by complex anthropogenic emissions, mineral dust and marine emissions, and the contribution of anthropogenic emissions is dominant. © 2024 Chinese Society for Environmental Sciences. All rights reserved.